1) Why the storm does not develop from equator to 5 degrees N/SLatitude?Because of coriolis force is too weak.claiming that Coriolis is too small for storm circulation

GENERAL OVERVIEWTropical Cyclone is the generic name for all hurricanes, typhoons, cyclones etc. They all have a unique character of Revolving about a centre and so are also called Revolving Storms. To understand the term ‘Revolving’, if you keep a bucket of water and try to stir it such that both the upper and the lower layers of the water are rotating in your direction of stir, leaving a hollow in the middle of the bucket from the top to the bottom (equivalent to the ‘eye’ of the storm in a real tropical cyclone), then that is a perfect description of how a tropical cyclone behaves, the difference being that the bucket of water is the microscale while the real thing has a diameter of at least 500km (312.5miles) and a height in the range of 10-15km. You may wonder why a storm should begin to rotate. Well, they acquire this character from the rotation of the earth itself. As they (the storms) move farther away from the equator, a factor known as the Coriolis Parameter (from Coriolis force - after the founder G.G de Coriolis, a French Physicist) becomes significant in the Atmospheric Motion Equation.The term ‘Tropical’ is a reflection of their ‘birth place’ as they all originate from tropical waters (oceans). The speed of associated winds is very critical for them to be termed tropical cyclones – they must reach or exceed 118km/h (74mph). The name Typhoon is used in the Western North Pacific Ocean (west of the international dateline), Hurricane in the North Atlantic, Papagallos in the Eastern North Pacific Ocean, Trovado near Madagascar, simply Cyclones in the Indian Ocean and Bay of Bengal, Willy-Willy in Australia, and Baguio in the Philippines.

FACTS ABOUT THE FORMATION OF TROPICAL CYCLONESTropical Cyclones do not form in regions within 5 degrees N or S of the Equator. The most favourable latitude belts are 5-15 degrees N or S. However in the Southern Hemisphere (SH) they do not form beyond 22 degrees S while in the Northern Hemisphere (NH) they still form in latitudes as high as 35 degrees N.There are 7 Tropical Cyclone Basins around the world where these types of storms occur on a regular basis: (i) The Atlantic Basin (including the North Atlantic, the Gulf of Mexico, and the Caribbean Sea). (ii) Northeast Pacific Basin (from the coast of Mexico to 140 degrees west longitude). (iii) North Central and Northwest Pacific Basin (from 140 degrees west, through the international dateline to the Philippine and south China seas). (iv) North Indian Basin (the Bay of Bengal and the Arabian Sea). (v) Southwest Indian Ocean Basin (from about 100 degrees east to the south eastern coast of Africa. (vi) Southeast Indian Ocean/Australian basin (from about 100 degrees east to the northwest coast of Australia. (vii) Australia/Southwest Pacific Basin (from the eastern coasts of Australia to areas beyond the international dateline).  Research has shown that two-thirds of all Tropical Cyclones form in the eastern hemisphere – the tropical northeast Pacific (off the coast of Mexico), the south China and the Philippine seas and the Bay of Bengal. The other one-third form in the tropical waters of the West Indies and the Gulf of Mexico, the stretch of SH tropical ocean from around the International dateline (Between 170 degrees E and 180 ) through Australia to the coasts of Africa.On rare occasions, tropical cyclones (or tropical/subtropical systems appearing to be similar to tropical cyclones) can develop in the Mediterranean Sea. Although the majority of tropical cyclones form in the summer, genesis is possible in all seasons in the western north Pacific (south China and the Philippine seas – this region alone is reputed to have nearly one-third of all the globe’s tropical cyclones).The southeast Pacific (off the coasts of Chile and Peru) and south Atlantic (the Atlantic waters between Africa and Latin America) are not affected by cyclones.Cyclones formation is especially favoured near the location of the ITCZ (Inter tropical Convergence Zone – the zone of the convergence of NH and SH air masses particularly over the ocean). 80-85% of these cyclones originate in or just on the poleward side of the ITCZ. The Sea Surface Temperature (SST) is usually above 26 degrees C (79 degrees F) to a depth of 60m.

2) What is the meaning of one prolonged and two short blasts / vesselto display during restricted visibility?

1 - vessel not under command,2 - vessel restricted in her ability to maneuver,3 - vessel constrained by her draft, 4 - sailing vessel,5 - vessel engaged in fishing and 6 - vessel engaged in towing or pushing another vessel shall, instead of the signals prescribed in paragraphs (a) or (b) of this Rule, sound at intervals of not more than 2 minutes three blasts in succession, namely one prolonged followed by two short blasts.

3)Why passing Aleutian sea?

The Northern Great Circle route of the North Pacific OceanA great circle is the shortest distance between two points on a sphere. Vessels transiting an ocean between two continents may follow a great circle route because it is the shortest distance, or they may deviate from the great circle route where favorable weather and sea states allow for faster travel.

On many map projections a great circle route is not a straight line. Figure 1 shows a gnomonic map projection of the North Pacific where the great circle route is a straight line. As seen on this map, a great circle route from Yokohama, Japan to Seattle passes through Unimak Pass and the Aleutian Islands. Figure 2 shows this same route on a Mercator projection where, because the map is flat and the earth is curved, the route appears as a “great circle,” or more accurately, a semi-circle.

- avoiding typhoons during

4) Maritime traffic Safety Law of Japan, what items should be compliedby the vessel

5) Statical stability

Centre of GravityA point on the vessel through which all forces of gravity act vertical downwards

Forces of GraphicAll forces of gravity acting vertically downwards

Centre of BuoyancyA point on the vessel through which all forces of buoyancy act vertically upwards equal to the water displaced

Forces of BuoyancyA floating body experiences an upward force equal to the water it displaces

MetacentreA point on the centre-line of a vessel through which all the forces of buoyancy pass when the vessel is heeled

Righting LeverWhen the vessel is heeled by an external force, the centre of buoyancy/centre of gravity are not in the same line, now a horizontal distance exists, the buoyancy pushing the vessel upright (the righting lever Gz)

Metacentric HeightThe distance from the Centre of Gravity to the Metacentre (G.M.)

Height of the MetacentreThe distance from the Keel to the Metacentre (K.M.)

DisplacementIs the total weight of the vessel equal to the water it displaces

(Displacement = Lightship + deadweight

DraughtThe vertical distance from the Keel to the waterline

FreeboardThe vertical distance from the waterline to the lowest deck-edge

Under keel allowanceThe distance from the keel to the seabed

TrimThis is the difference between the fore and aft draughts

Mean DraftThis is the forward and aft draft added together and divided by the number 2

Stable EquilibriumThis is when a vessel has a positive righting lever (G below M)

Neutral EquilibriumThis is when the vessel has no righting lever (G & M together) (Danger of Capsize)

Unstable EquilibriumThis is when the vessel has a negative righting lever (G above M) (Capsizing lever)

Stiff VesselThis is a vessel with a very large righting lever (G near the Keel)

Tender VesselThis is a vessel with a vessel small righting lever (G very near M)

Angle of LollThis is a vessel that is initial unstable but when heeled has a vessel small righting lever (Very dangerous condition, get rid of any weights on deck either by putting it overboard or down into the hold) (Caution watch an angle of loll through ice accretion, always take the ice off all rigging first the from the high side and push it towards the low side giving you a bigger list but your forces of buoyancy work harder to keep your vessel upright)

ListA list is caused by you moving anything on the vessel to one side

Curve of Statical Stabilitythis is a curve that shows the following :(1.) angle of maximum stability(2.) maximum g.z.(3.) the righting lever at any angle

(4.) angle of vanishing stability(5.) the range of stability(6.) angle where deck-edge immersion begins(7.) the amount of dynamic stability a vessel has(8.) the point of contra flexure(9.) the angle of inclination(10.) the initial g.m.(11.) the radians for that vessel

StabilityThis is an act of keeping the vessel stable

Transverse or Statical StabilityThe vessels ability to return to the upright position

Reserve BuoyancyThis is the volume of air trapped in a watertight space above the waterline

Centre of FloatationThis is the centre of the water-plane area of a vessel at any draught

DeadweightThis is the cargo, stores water, fuel that you've taken aboard

Light DisplacementThe total weight of the vessel, machinery etc that stays on the vessel and cannot be moved, (stores, fuel water etc not included)

LightshipThe total weight of the vessel, machinery etc that stays on the vessel and cannot be moved, (stores, fuel water etc not included)

A righting moment or a moment of statical stabilityThe total weight X the righting lever (Gz)

A momentA moment = weight x distance

Loaded weight regarding the centre of gravityWhen a weight is loaded onto a vessel the centre of gravity moves towards it

Discharged weight regarding the centre of gravityWhen a weight is discharged from a vessel the centre of gravity goes back to where it was before the weight came on board (Opposite direction from where the weight was placed at on the vessel)

Shifted weight regarding the centre of gravityWhen a weight is shifted on a vessel the centre of gravity moves from where the weight was to the weights new position

Dynamic stabilityThe amount of work taken to bring a vessel back to its upright position

Range of positive stabilityThis is on a curve of statical stability , where the curve starts on the angle of inclination to where the curve stops at the point of vanishing stability

Angle of vanishing stabilityThis is on the curve of statical stability and where the curve comes down and has no (g.z.) ( + or - ) then this is where stability vanishes

Initial GMThis is on the curve of statical stability, on the angle of inclination at 57.3 degrees there is a radian line , and a tangent line which starts from 0 degrees and leaves the first arc of the curve of statical stability and where the tangent line and the radian line at 57.3 degrees meet then this is the initial g.m.

Angle of Maximum stabilityThis is on the curve of statical stability, on the curve itself at the top of the curve down to the angle of inclination and this is the angle of maximum stability

Maximum GZ (on curve of static stability)This is on the curve of statical stability, at the top of the curve look at the distance on the scale (metres) and this is the maximum g.z.

Importance of adequate freeboardWith freeboard raised then this will give you(1.) a greater range of stability(2.) a greater range of vanishing stability(3.) a greater maximum g.z.(4.) the maximum g.z. occurs at a greater angle(5.) greater dynamic stability

DensityThe mass of any object expressed in cubic metres(i.e.) a dice is length x breadth x width =

Volume of displacementThis is where the vessel is equal to the water displaced and expressed in cubic metres

6) G/M?This is on the curve of statical stability, on the angle of inclination at 57.3 degrees there is a radian line , and a tangent line which starts from 0 degrees and leaves the first arc of the curve of statical stability and where the tangent line and the radian line at 57.3 degrees meet then this is the initial g.m.

7) K/M?METACENTREVertical lines drawn from the centre of buoyancy at consecutive small angles of heel will intersect at a point called the metacentre (M). The metacentrecan be considered as being similar to a pivot point when a vessel is inclined at small angles of heel. The height of the metacentre is measured from the reference point (K) and is, therefore, called KM

8) Formula Consumption (fuel)? specific fuel consumption is calculated by the equation: SFC = F/P x 1000 , wherein: SFC is the specific fuel consumption, F is the fuel consumption in kg/hour and P is the shaft horsepower in HP; the hull performance is calculated by the equation: H = S x 1853/P , wherein H is the hull performance; S is the speed in knots; P is the shaft horsepower in HP; and 1853 is the conversion factor from nautical miles to metres; andthe overall performance is calculated by the equation: O = S/F x 1000 , wherein O is the overall performance;

S is the speed in knots; and F is the fuel consumption in kg/hour.

9) Extra-tropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth (outside the tropics) having neither tropical nor polar characteristics, and are connected with fronts and horizontal gradients in temperature and dew point otherwise known as "baroclinic zones".[1] Extratropical cyclones are the everyday phenomena which, along with anticyclones, drive the weather over much of the Earth, producing anything from cloudiness and mild showers to heavy gales and thunderstorms. Extratropical cyclones form anywhere within the extratropical regions of the Earth (usually between 30° and 60° latitude from the equator), either through cyclogenesis or extratropical transition. A study of extratropical cyclones in the Southern Hemisphere shows that between the 30th and 70th parallels, there are an average of 37 cyclones in existence during any 6-hour period.[4] A separate study in the Northern Hemisphere suggests that approximately 234 significant extratropical cyclones form each winter.[5 Extratropical transition

Hurricane Florence in the north Atlantic after completing its transition to an extratropical cyclone from a hurricane

Tropical cyclones often transform into extratropical cyclones at the end of their tropical existence, usually between 30° and 40° latitude, where there is sufficient forcing from upper-level troughs or shortwaves riding the Westerlies for the process of extratropical transition to begin. During extratropical transition, the cyclone begins to tilt back into the colder airmass with height, and the cyclone's primary energy source converts from the release of latent heat from condensation (from thunderstorms near the center) to baroclinic processes. The low pressure system eventually loses its warm co-+++

re and becomes a cold-core system. During this process, a cyclone in extratropical transition (known in Canada as the post-tropical stage)[13] will invariably form or connect with nearby fronts and/or troughs consistent with a baroclinic system. Due to this, the size of the system will usually appear to increase, while

the core weakens. However, after transition is complete, the storm may re-strengthen due to baroclinic energy, depending on the environmental conditions surrounding the system. The cyclone will also distort in shape, becoming less symmetric with time.

On rare occasions, an extratropical cyclone can transit into a tropical cyclone if it reaches an area of ocean with warmer waters and an environment with less vertical wind shear. The peak time of subtropical cyclogenesis (the midpoint of this transition) is in the months of September and October, when the difference between the temperature of the air aloft and the sea surface temperature is the greatest, leading to the greatest potential for instability.[14] The process known as "tropical transition" involves the usually slow development of an extratropically cold core vortex into a tropical cyclone.[15][16]

10) virtual rise?11) One way traffic (Japan-Maritime Traffic Safety Law)12) How many satellite in the GPS (24 satelita u sistemu + 4 rezerva)13) Accuracy of GPS - 2 dimensional and 3 dimensional?

GPS accuracy is affected by a number of factors, including satellite positions, noise in the radio signal, atmospheric conditions, and natural barriers to the signal. Noise can create an error between 1 to 10 meters and results from static or interference from something near the receiver or something on the same frequency. Clouds and other atmospheric phenomena, and objects such a mountains or buildings between the satellite and the receiver can also produce error, sometimes up to 30 meters. The most accurate determination of position occurs when the satellite and receiver have a clear view of each other and no other objects interfere. Obviously, mountains and clouds can not be controlled or moved, nor can interference and blockage from buildings always be prevented. These factors then, will affect GPS accuracy. To overcome or get around these factors, other technology, AGPS, DGPS, and WAAS, has been developed to aid in determining an accurate location. AGPS (Assisted Global Positioning System) is a system that assists conventional GPS when reception of the radio signal from the satellite is poor or non-existent (line of sight is blocked). To aid in GPS accuracy, the AGPS gains information via a wireless network, such as the GPS receivers on cell towers, to relay the satellite information to the receiver. With this assistance, the GPS doesn't have to calculate the satellite's orbit, which shortens initialization time, and increases battery life.

Differential GPS

To further increase accuracy, DGPS (Differential Global Positioning System) technology was developed. Like the AGPS, the DGPS uses a fixed GPS location (such as a cell tower) to send information to the GPS receiver. DGPS, however, looks at both the satellite and the fixed location adjusts for any difference between the two, and then sends that information to the receiver. DGPS is particularly helpful when atmospheric conditions interfere with reception.

The most recent innovation in GPS technology is the WAAS (Wide Area Augmentation System) developed by the FAA and DOD to augment GPS for air navigation. Utilizing a network of ground-based stations (WRS or Wide-area Reference Stations) which are protected from the public, WAAS transmits corrections to geosynchronous communications satellites, which then transmit the corrections to the user. WAAS was designed to allow aircraft to rely on GPS for all phases of flights, including precision, or "instrument only" landings. Specifications for WAAS require accuracy of 7 meters or better both vertically and laterally, 95% of the time. In practice, WAAS achieved a lateral accuracy of 1 meter and of 1.5 meters vertically when over the contiguous United States. Read more on how WAAS works at WAAS Explained.

Many GPS manufacturers market their products as the more accurate, or having greater sensitivity than their competitors, but the bottom line is that GPS accuracy depends on the GPS technology in use.

Global Positioning System (GPS) units in telemetry collars provide an unbiased and precise estimate of animal locations. Under ideal conditions at least 50% of locations are expected to be within 40 m in uncorrected mode GPS, and within 5 m in differential mode GPS. When the collar was placed under open sky, most locations were 3-dimensional locations that could be differentially corrected. Under hardwood canopies with leaves on, the frequency of 3-dimensional locations decreased, the frequencies of failed location attempts and 2-dimensional locations increased, and the precision of GPS locations decreased. We compared the precision of each GPS mode by calculating uncorrected mode and differential mode locations from the same pseudo-range and ephemeris data. We varied the number of satellites used in the location solution to simulate the effect of decreased satellite acquisition due to canopy cover on precision of locations. Precision of locations increased if signals from >4 satellites were used to calculate the location in uncorrected mode and in differential mode. We found that 2-dimensional locations were almost as precise as 3-dimensional positions if the altitude of the GPS unit was known. If the altitude used to calculate a 2-dimensional location was within 50 m of the actual collar altitude, the precision of 2-dimensional differential mode locations was better than 3-dimensional uncorrected mode locations. If the error in altitude was 100 or 150 m, then 50% of 2-dimensional differential mode locations were within 70 m and 95% were within 185 m of the true location. We used GPS locations from collars placed in different cover types and on free-ranging moose (Alces alces) to determine the effect of season, time of day, rainfall, and cover type on GPS performance. On free-ranging moose the collar GPS unit found ≥4 satellites on 52% of location attempts, >50% of locations were 3-dimensional, and >24% of locations were 2-dimensional. Precise tracking of individual animals in all weather throughout the year is possible with GPS telemetry.

14) What can you observed when a vessel navigating in shallow water

A ship moving through shallow water experiences pronounced effects from the proximity of the nearby bottom. Similarly, a ship in a channel will be affected by the proximity of the sides of the channel. These effects can easily cause errors in piloting which lead to grounding. The effects are known as squat, bank cushion, and bank suction. They are more fully explained in texts on ship handling, but certain navigational aspects are discussed below.

Squat is caused by the interaction of the hull of the ship, the bottom, and the water between. As a ship moves through shallow water, some of the water it displaces rushes under the vessel to rise again at the stern. This causes a venturi effect, decreasing upward pressure on the hull. Squat makes the ship sink deeper in the water than normal and slows the vessel. The faster the ship moves through shallow water, the greater is this effect; groundings on both charted and uncharted shoals and rocks have occurred because of this phenomenon, when at reduced speed the ship could have safely cleared the dangers. When navigating in shallow water, the navigator must reduce speed to avoid squat. If bow and stern waves nearly perpendicular the direction of travel are noticed, and the vessel slows with no change in shaft speed, squat is occurring. Immediately slow the ship to counter it. Squatting occurs in deep water also, but is more pronounced and dangerous in shoal water. The large waves generated by a squatting ship also endanger shore facilities and other craft.

Bank cushion is the effect on a ship approaching a steep underwater bank at an oblique angle. As water is forced into the narrowing gap between the ship's bow and the shore, it tends to rise or pile up on the landward side, causing the ship to sheer away from the bank.

Bank suction occurs at the stern of a ship in a narrow channel. Water rushing past the ship on the landward side exerts less force than water on the opposite or open water side. This effect can actually be seen as a difference in draft readings from one side of the vessel to the other, and is similar to the venturi effect seen

in squat. The stern of the ship is forced toward the bank. If the ship gets too close to the bank, it can be forced sideways into it. The same effect occurs between two vessels passing close to each other.

These effects increase as speed increases. Therefore, in shallow water and narrow channels, navigators should decrease speed to minimize these effects. Skilled pilots may use these effects to advantage in particular situations, but the average mariner's best choice is slow speed and careful attention to piloting.

15) Huge vessel-lights and day signal

InJapanese waters, ‘huge’ vessels (more than 200m long) arerequired to exhibit a flashing green light. A green all-round light to be visible at a distance of at least 2 miles and flashing at regular intervals between 180 and 200 times per minute. Two black cylinders with a diameter of 0.6 meter or more and a height twice as long as the diameter which are placed in a vertical line not less than 1.5 meters apart (with regard to a huge vessel which exhibits a cylinder in accordance with Article 28 of the Law for Preventing Collisions at Sea, these shapes shall not be placed with the cylinder in a vertical line.) Vessels carrying dangerous goods A red all-round light to be visible at a distance of at least 2 miles and flashing at regular intervals between 120 and 140 per minute. International Code Flag B under First Substitute.

16) Height of GPS sattellite (odgovor 20,000 km)

There is a constellation of at least 24 GPS satellite in orbit around the earth. Each orbit takes 11 hours 58 minutes to complete and inclination and positioning of the satellites around the orbits is arranged so that wherever you are there should be several satellites visible in the sky above you. The satellite are about 20200 km high, a little less than half the height of the 24 hour orbits of the geostationary satellite. Go here for current GPS satellite status.    The number of operational satellites varies as older ones are retired and new ones are launched, but is typically in the range 24 to 30 in orbit at any time. Go here for GPS satellite launch dates.

Each GPS satellite broadcasts a high power, narrow bandwidth, downlink signal that may be received on your small hand held receiver antenna.

Your receiver receives signals simultaneously from all the visible satellites. The downlink frequency is in L band at 1575.42 MHz and comprises a signal intended for public use called the coarse/acquisition code or C/A-code.  Another signal is used by military receivers to achieve higher precision latitude-longitude positioning results. 

Each satellite has an on-board timing clock (using cesium or rubidium atomic standards) so that it knows what is the time to very high precision and it is able then to transmit signals down at exactly known instants. The signals come down to your receiver at the speed of light ( 300,000 kilometres per second or 300 metres per micro-second ) and the time of arrival of the signals at your receiver is what matters. A computer program in your receiver notes the time of arrival of the signals received from the various visible GPS satellites and is able to work out your latitude and longitude position and also your height. If your position is changing, by observing the changes it is possible to work out the speed of your movement and the direction in which you are moving.

The system needs at least 3 satellite to obtain a latitude and longitude fix. Four satellites allows your height to be determined as well and the more satellites that can be received, this higher the accuracy of the results. The accuracy varies according to the location of the satellites. If four satellites were visible but all close together in the sky then the accuracy would be worse then is they were spaced out widely across the sky.  Many GPS receivers have an optional display that shows where the satellite are, like overhead, towards the east or west etc. If you keep the receiver still, it will average readings over a long time to improve the accuracy.

Accuracy depends on several factors:  Tropospheric delays: The amount of moisture in the atmosphere slows down the signals slightly, particularly if they arrive from a satellite just above the horizon and uncertainty in this degrades the accuracy of the timing calculation.   Orbit ephemeris data accuracy: The satellites each have on board some data which describes their orbital parameter (orbit ephemeris figures) and they broadcast this data to your receiver so that your receiver can work out where the satellite was when it transmitted. The orbit ephemeris are updated frequently using ground based measurements, but any errors will affect the positioning results.  Multi-path reflection: Sometimes there are nearby buildings reflections will affect the accuracy. If you are in a road with tall buildings either side signal may arrive at your receiver via reflections.   Deliberate errors: Because accurate location information is of military significance, the accuracy of the publicly available system may be degraded or even turned off. In the early days of GPS, the public system always had moderate errors. This was called Selective Availability. Selective Availability was turned off in May 2000 to allow soldiers using shop bought GPS receiver to achieve their required accuracy and the system has be left in this mode since.

Extremely high accuracy latitude-longitude positioning is possible if you use differential GPS. In this case you need two receivers. You fix one receiver precisely and call this your reference location, for example at the corner of a field. At this reference receiver you make a record of the long term average (accurate) location and also the instantaneously displayed location (less accurate) and note the differences. You then

broadcast locally (using a radio) the differences, which will vary second by second due to atmospheric effects etc. You then move the other receiver around locally together with a receiver of your differential correction data and add or subtract the differences from the readings observed. Differential GPS was of great benefit before May 2000, while Selective Availability was applied.

17) Eleven traffic zone (Japan-Maritime Traffic Safety Law) -Uraga Suido Traffic Route -Naka-no-Se Traffic Route, -Irago Suido Traffic Route, --Uko East Traffic Route, -Uko West Traffic Route, -Bisan Seto North Traffic Route, -Bisan Seto South Traffic Route, -Bisan Seto East Traffic Route -Mizushima Traffic Route and -Kurushima Kaikyo Traffic Route, -Akashi Kaikyo Traffic Route,

18) Cold frontA cold front is defined as the leading edge of a cooler and drier mass of air, replacing (at ground level) a warmer mass of air.

symbol

Development of cold front

The cooler, denser air wedges under the less dense warmer air, lifting it, which can cause the formation of a narrow line of showers and thunderstorms when enough moisture is present. This upward motion causes lowered pressure along the cold front. On weather maps, the surface position of the cold front is marked with the symbol of a blue line of triangles/spikes (pips) pointing in the direction of travel. A cold front's location is at the leading edge of the temperature drop off, which in an isotherm analysis would show up as the leading edge of the isotherm gradient, and it normally lies within a sharp surface trough. Cold fronts can move up to twice as fast and produce sharper changes in weather than warm fronts. Since cold air is denser than warm air, it rapidly replaces the warm air preceding the boundary. Cold fronts, are usually associated with an area of low pressure, and sometimes, a warm front.

In the northern hemisphere, a cold front usually causes a shift of wind from southeast to northwest, and in the southern hemisphere a shift from northeast to southwest. Common characteristics associated with cold fronts include:

Weather phenomenon Prior to the Passing of the Front

While the Front is Passing

After the Passing of the Front

Temperature Warm Cooling suddenly Steadily cooling

Atmospheric pressure Decreasing steadily Lowest, then sudden increase Increasing steadily

Winds

Southwest to southeast (northern hemisphere)

Northwest to northeast (southern hemisphere)

Gusty; shifting

North to west (usually northwest) (northern hemisphere)

South to west (usually southwest) (southern hemisphere)

Precipitation/conditions* Brief showers Thunderstorms, sometimes severe

Showers, followed by clearing

Clouds* Increasing: Cirrus, cirrostratus, and cumulonimbus Cumulonimbus Cumulus

Visibility* Fair to poor in haze Poor, but improving Good, except in showers

Dew Point High; steady Sudden drop Falling

18) Radar-bearing resolution/range resolution: false echo

The ability of a radar to separate targets close together on the same bearing is called resolution in range. It is related primarily to pulse length. The minimum distance between targets that can be distinguished as separate is half the pulse length. This (half the pulse length) is the apparent depth or thickness of a target presenting a flat perpendicular surface to the radar beam. Thus, several ships close together may appear as an island. Echoes from a number of small boats, piles, breakers, or even large ships close to the shore may blend with echoes from the shore, resulting in an incorrect indication of the position and shape of the shoreline.

• Resolution in Bearing. Echoes from two or more targets close together at the same range may merge to form a single, wider echo. The ability to separate targets close together at the same range is called resolution in bearing. Bearing resolution is a function of two variables: beam width and range to the targets. A narrower beam and a shorter distance to the objects both increase bearing resolution.

Indirect or false echoes are caused by reflection of the main lobe of the radar beam off ship’s structures such as stacks and kingposts. When such reflection does occur, the echo will return from a legitimate radar contact to the antenna by the same indirect path. Consequently, the echo will appear on the PPI at the bearing of the reflecting surface. As shown in Figure 1307a, the indirect echo will appear on the PPI at the same range as the direct echo received, assuming that the additional distance by the indirect path is negligible.

Characteristics by which indirect echoes may be recognized are summarized as follows: 1. Indirect echoes will often occur in shadow sectors. 2. They are received on substantially constant bearings, although the true bearing of the radar contact may change appreciably. 3. They appear at the same ranges as the corresponding direct echoes. 4. When plotted, their movements are usually abnormal. 5. Their shapes may indicate that they are not direct echoes.

Side-lobe effects are readily recognized in that they produce a series of echoes (Figure 1307b) on each side of the main lobe echo at the same range as the latter. Semicircles, or even complete circles, may be produced. Because of the low energy of the side-lobes, these effects will normally occur only at the shorter ranges. The effects may be minimized or eliminated, through use of the gain and anti-clutter controls. Slotted wave guide antennas have largely eliminated the side-lobe problem.

Multiple echoes may occur when a strong echo is received from another ship at close range. A second or third or more echoes may be observed on the radarscope at double, triple, or other multiples of the actual range of the radar contact (Figure 1307c).

Second-trace echoes (multiple-trace echoes) are echoes received from a contact at an actual range greater than the radar range setting. If an echo from a distant target is received after the following pulse has been transmitted, the echo will appear on the radarscope at the correct bearing but not at the true range. Second-trace echoes are unusual, except under abnormal atmospheric conditions, or conditions under which super-refraction is present. Second trace echoes may be recognized through changes in their positions on the radarscope in changing the pulse repetition rate (PRR); their hazy, streaky, or distorted shape; and the erratic movements on plotting.

As illustrated in Figure 1307d, a target return is detected on a true bearing of 090° at a distance of 7.5 miles. On changing the PRR from 2,000 to 1,800 pulses per second, the same target is detected on a bearing of 090° at a distance of 3 miles (Figure 1307e). The change in the position of the return indicates that the return is a second-trace echo. The actual distance of the target is the distance as indicated on the PPI plus half the distance the radar wave travels between pulses.

Electronic interference effects, such as may occur

Figure 1306c. Distortion effects of radar shadow, beam width, and pulse length.

when near another radar operating in the same frequency band as that of the observer’s ship, is usually seen on the PPI as a large number of bright dots either scattered at random or in the form of dotted lines extending from the center to the edge of the PPI.

Interference effects are greater at the longer radar range scale settings. The interference effects can be distinguished easily from normal echoes because they do not appear in the same places on successive rotations of the antenna.

Stacks, masts, samson posts, and other structures, may cause a reduction in the intensity of the radar beam beyond these obstructions, especially if they are close to the radar antenna. If the angle at the antenna subtended by the obstruction is more than a few degrees, the reduction of the intensity of the radar beam beyond the obstruction may produce a blind sector. Less reduction in the intensity of the beam beyond the obstructions may produce shadow sectors. Within a shadow sector, small targets at close range may not be detected, while larger targets at much greater ranges will appear.

19) Sound signal passing Kurushima Kaiyo

(Kurushima Kaikyo Traffic Route) Article 10.The direction of tidal current to be indicated by the Commandant of the Japan Coast Guard under Article 20 Paragraph 2 of the Law shall be such directions as will be indicated by means of tidal signal at Kurushima Nagasenohana Tidal Current Signal Station (34゜06'23"N,133゜02'10"E), Nakato Shima Tidal Current Signal Station (34゜06'53"N,133゜00'15"E), Ohama Tidal Current Signal Station (34゜05'12"N,132゜59'38"E), Tsu Shima Tidal Current Signal Station (34゜08'51"N,132゜59'38"E) or Kurushima Osumibana Tidal Current Signal Station (34゜08'13"N,132゜56' 37"E). 2. Signals to be given in such case as mentioned in each of the following items, in accordance with the provisions of Article 21 Paragraph 1 of the Law shall be such signals as prescribed in each of the same items: (1) In the case mentioned in Article 21 Paragraph 1 item(1) of the Law (only such cases as related to Naka Suido): One prolonged blast on the whistle at frequent intervals from the time when the vessel has lchinose Hana on Tsu Shima or Ryujin Shima on her beam until she is finally past and clear Naka Suido; (2) In the case mentioned in Article 21 Paragraph 1 item (1) of the Law (only such cases as related to Nishi Suido): Two prolonged blasts on the whistle at frequent intervals from the time when the vessel has lchinose Hana on Tsu Shima or Ryujin Shima on her beam until she is finally past and clear Nishi Suido; (3) In the case mentioned in Article 21 Paragraph 1 item (2) of the Law: Three prolonged blasts on the whistle at frequent intervals from the time when the vessel has Kuru Shima or Ryujin Shima on her beam until she is finally past and clear Nishi Suido. 3. The sea areas to be prescribed by the Ministry of LIT Ordinance referred to in Article 21 Paragraph 2 of the Law shall be those areas (excluding the area of Kurushima Kaikyo Traffic Route) which are surrounded by the line drawn from the extremity (34゜03'22"N,133゜01'22"E) of the right bank at the estuary of Soja Kawa to Take-no-Hana on O Shima, by the lines drawn from Ago-no-Hana on Oge Shima to Kajitori-no-Hana and to Miya-no-Hana on O Shima, respectively, and by shorelines.

21) Formula of rolling period

GM and rolling period

GM has a direct relationship with a ship's rolling period. A ship with a small GM will be "tender" - have a long roll period - an excessively low or negative GM increases the risk of a ship capsizing in rough weather (see HMS Captain or the Vasa). It also puts the vessel at risk of potential for large angles of heel if the cargo or ballast shifts (see Cougar Ace). A ship with low GM is less safe if damaged and partially flooded because the lower metacentric height leaves less safety margin. For this reason, maritime regulatory

agencies such as the IMO specify minimum safety margins for sea-going vessels. A larger metacentric height, on the other hand can cause a vessel to be too "stiff"; excessive stability is uncomfortable for passengers and crew. This is because the stiff vessel quickly responds to the sea as it attempts to assume the slope of the wave. An overly stiff vessel rolls with a short period and high amplitude which results in high angular acceleration. This increases the risk of damage to the ship as well as the risk cargo may break loose or shift. In contrast a "tender" ship lags behind the motion of the waves and tends to roll at lesser amplitudes. A passenger ship will typically have a long rolling period for comfort, perhaps 12 seconds while a tanker or freighter might have a rolling period of 6 to 8 seconds.

The period of roll can be estimated from the following equation[2]

Where g is the gravitational constant, k is the radius of gyration about the longitudinal axis through the center of gravity and GM is the stability index

22) ARPA

A maritime radar with Automatic Radar Plotting Aid (ARPA) capability can create tracks using radar contacts. The system can calculate the tracked object's course, speed and closest point of approach (CPA), thereby knowing if there is a danger of collision with the other ship or landmass.

Development of ARPA started after the accident when the Italian liner SS Andrea Doria collided in dense fog and sank off the east coast of the United States. ARPA radars started to emerge in the 1960s and, with the development of microelectronics. The first commercially available ARPA was delivered to the cargo liner MV Taimyr in 1969[1] and was manufactured by Norcontrol, now a part of Kongsberg Maritime The International Maritime Organization (IMO) has set out certain standards amending the International Convention for the Safety of Life at Sea requirements regarding the carrying of suitable automated radar plotting aids. The primary function of ARPAs can be summarized in the statement found under the IMO Performance Standards. It states a requirement of ARPAs...."in order to improve the standard of collision avoidance at sea: Reduce the workload of observers by enabling them to automatically obtain information so that they can perform as well with multiple targets as they can by manually plotting a single target". As we can see from this statement the principal advantages of ARPA are a reduction in the workload of bridge personnel and fuller and quicker information on selected targets.

A typical ARPA gives a presentation of the current situation and uses computer technology to predict future situations. An ARPA assesses the risk of collision, and enables operator to see proposed maneuvers by own ship.

While many different models of ARPAs are available on the market, the following functions are usually provided:

1. True or relative motion radar presentation.2. Automatic acquisition of targets plus manual acquisition.3. Digital read-out of acquired targets which provides course, speed, range, bearing, closest point of

approach (CPA, and time to CPA (TCPA).

4. The ability to display collision assessment information directly on the PPI, using vectors (true or relative) or a graphical Predicted Area of Danger (PAD) display.

5. The ability to perform trial maneuvers, including course changes, speed changes, and combined course/speed changes.

6. Automatic ground stabilization for navigation purposes. ARPA processes radar information much more rapidly than conventional radar but is still subject to the same limitations. ARPA data is only as accurate as the data that comes from inputs such as the gyro and speed log.

AAA) MARITIME LAW:

1) Eleven Traffic Routes - one way traffic routes/two way trafficroutes

2) Vessels which receive special treatment

3) Keeping out of the way of other vessels (obligation)

4) Restiriction of speed

5) Signaling in case of overtaking

6) Indication of destination

7) Display of lights and markings

BBB) COLREGS:1) Different kinds of signal in restricted visibility (sound signal)

RULE 35

Sound Signals in Restricted Visibility

In or near an area of restricted visibility, whether by day or night, the signals

prescribed in this Rule shall be used as follows:

(a) A power-driven vessel making way through the water shall sound at

ntervals of not more than 2 minutes one prolonged blast.

(b) A power-driven vessel underway but stopped and making no way

through the water shall sound at intervals of not more than 2 minutes two

prolonged blasts in succession with an interval of about 2 seconds between

them.

(c) A vessel not under command, a vessel restricted in her ability to

maneuver, a vessel constrained by her draft, a sailing vessel, a vessel

engaged in fishing and a vessel engaged in towing or pushing another

vessel shall, instead of the signals prescribed in paragraphs (a) or (b) of this

Rule, sound at intervals of not more than 2 minutes three blasts in

succession, namely one prolonged followed by two short blasts.

(d) A vessel engaged in fishing, when at anchor, and a vessel restricted in

her ability to maneuver when carrying out her work at anchor, shall instead

of the signals prescribed in paragraph (g) of this Rule sound the signal

prescribed in paragraph (c) of this Rule.

(e) A vessel towed or if more than one vessel is towed the last vessel of

the tow, if manned, shall at intervals of not more than 2 minutes sound four

blasts in succession, namely one prolonged followed by three short blasts.

When practicable, this signal shall be made immediately after the signal

made by the towing vessel.

(f) When a pushing vessel and a vessel being pushed ahead are rigidly

connected in a composite unit they shall be regarded as a power-driven

vessel and shall give the signals prescribed in paragraphs (a) or (b) of this

Rule.

RULE 35

Sound Signals in Restricted Visibility

In or near an area of restricted visibility, whether by day or night, the signals

prescribed in this Rule shall be used as follows:

(a) A power-driven vessel making way through the water shall sound at

intervals of not more than 2 minutes one prolonged blast.

(b) A power-driven vessel underway but stopped and making no way

through the water shall sound at intervals of not more than 2 minutes two

prolonged blasts in succession with an interval of about 2 seconds between

them.

(c) A vessel not under command; a vessel restricted in her ability to

maneuver, whether underway or at anchor; a sailing vessel; a vessel

engaged in fishing, whether underway or at anchor; and a vessel engaged

in towing or pushing another vessel shall, instead of the signals prescribed

in paragraphs (a) or (b) of this Rule, sound at intervals of not more than 2

minutes, three blasts in succession; namely, one prolonged followed by two

short blasts.

(d) A vessel towed or if more than one vessel is towed the last vessel of

the tow, if manned, shall at intervals of not more than 2 minutes sound four

blasts in succession; namely, one prolonged followed by three short blasts.

When practicable, this signal shall be made immediately after the signal

made by the towing vessel.

(e) When a pushing vessel and a vessel being pushed ahead are rigidly

connected in a composite unit they shall be regarded as a power-driven

vessel and shall give the signals prescribed in paragraphs (a) or (b) of this

Rule.

RULE 35—CONTINUED

(g) A vessel at anchor shall at intervals of not more than one minute ring

the bell rapidly for about 5 seconds. In a vessel of 100 meters or more in

length the bell shall be sounded in the forepart of the vessel and

immediately after the ringing of the bell the gong shall be sounded rapidly

for about 5 seconds in the after part of the vessel. A vessel at anchor may in

addition sound three blasts in succession, namely one short, one prolonged

and one short blast, to give warning of her position and of the possibility of

collision to an approaching vessel.

(h) A vessel aground shall give the bell signal and if required the gong

signal prescribed in paragraph (g) of this Rule and shall, in addition, give

three separate and distinct strokes on the bell immediately before and after

the rapid ringing of the bell. A vessel aground may in addition sound an

appropriate whistle signal.

(i) A vessel of 12 meters or more but less than 20 meters in length shall

not be obliged to give the bell signals prescribed in paragraphs (g) and (h) of

this Rule. However, if she does not, she shall make some other efficient

sound signal at intervals of not more than 2 minutes.

(j) A vessel of less than 12 meters in length shall not be obliged to give the

above-mentioned signals but, if she does not, shall make some other

efficient sound signal at intervals of not more than 2 minutes.

(k) A pilot vessel when engaged on pilotage duty may in addition to the

signals prescribed in paragraphs (a), (b) or (g) of this Rule sound an identity

signal consisting of four short blasts.

Define safe speed:

RULE 6

Safe Speed

Every vessel shall at all times proceed at a safe speed so that she can

take proper and effective action to avoid collision and be stopped within a

distance appropriate to the prevailing circumstances and conditions.

In determining a safe speed the following factors shall be among those

taken into account:

(a) By all vessels:

(i) the state of visibility;

(ii) the traffic density including concentrations of fishing vessels or any

other vessels;

(iii) the maneuverability of the vessel with special reference to stopping

distance and turning ability in the prevailing conditions;

(iv) at night, the presence of background light such as from shore lights

or from back scatter of her own lights;

(v) the state of wind, sea and current, and the proximity of navigational

hazards;

(vi) the draft in relation to the available depth of water.

(b) Additionally, by vessels with operational radar:

(i) the characteristics, efficiency and limitations of the radar equipment;

(ii) any constraints imposed by the radar range scale in use;

(iii) the effect on radar detection of the sea state, weather and other

sources of interference;

(iv) the possibility that small vessels, ice and other floating objects may

not be detected by radar at an adequate range;

(v) the number, location and movement of vessels detected by radar;

(vi) the more exact assessment of the visibility that may be possible

when radar is used to determine the range of vessels or other objects

in the vicinity.

CCC) PORT REGULATION LAW:

1) Authority of Captain of port (COTP)

2) Definition: Miscellaneous vessel, specified port

3) Order of shift berths (reasons)

4) Steering and sailing rules concernig passages

DDD) STABILITY:

1) Definition/Explain: GM, KG, KM, GZ, Free surface efect, Stiff &Tender vessel, Stable/Neutral/Unstable equilibring shift OG G, FWA, Change of draft from SW to FW & vice versa. G/M?This is on the curve of statical stability, on the angle of inclination at 57.3 degrees there is a radian line , and a tangent line which starts from 0 degrees and leaves the first arc of the curve of statical stability and where the tangent line and the radian line at 57.3 degrees meet then this is the initial g.m.

KM- Vertical lines drawn from the centre of buoyancy at consecutive small angles of heel will intersect at a point called the metacentre (M). The metacentrecan be considered as being similar to a pivot point when a vessel is inclined at small angles of heel. The height of the metacentre is measured from the reference point (K) and is, therefore, called KM

KG - Center of Gravity

righting arm (known also as GZ — see diagram): the horizontal distance between the center of buoyancy and the center of gravity.[3]

GZ = GM sin φ [2]

Monohulled sailing vessels are designed to have a positive righting arm (the limit of positive stability) at anything up to 120º of heel, although as little as 90º (masts flat to the surface) is acceptable. As the

displacement of the hull at any particular degree of list is not proportional, calculations can be difficult and the concept was not introduced formally into naval architecture until about 1970

Free surface effect

Further information: Free surface effect

In tanks or spaces that are partially filled with a fluid or semi-fluid (fish, ice or grain for example) as the tank is inclined the surface of the liquid, or semi-fluid, stays level. This results in a displacement of the centre of gravity of the tank or space relative to the overall center of gravity. The effect is similar to that of carrying a large flat tray of water. When an edge is tipped, the water rushes to that side which exacerbates the tip even further.

The significance of this effect is proportional to the square of the width of the tank or compartment, so two baffles separating the area into thirds will reduce the displacement of the centre of gravity of the fluid by a factor of 9. This is always of significance in ship fuel tanks or ballast tanks, tanker cargo tanks, and in flooded or partially flooded compartments of damaged ships. Another worrying feature of free surface effect is that a positive feedback loop can be established, in which the period of the roll is equal or almost equal to the period of the motion of the centre of gravity in the fluid, resulting in each roll increasing in magnitude until the loop is broken or the ship capsizes.

Stable EquilibriumThis is when a vessel has a positive righting lever (G below M)

Neutral EquilibriumThis is when the vessel has no righting lever (G & M together) (Danger of Capsize)

Unstable EquilibriumThis is when the vessel has a negative righting lever (G above M) (Capsizing lever)

Stiff VesselThis is a vessel with a very large righting lever (G near the Keel)

Tender VesselThis is a vessel with a vessel small righting lever (G very near M)

Problem Solving: Rolling Period (in meter), Parallel sinkage, Change

of Trim, Change of Draft/FWA

GM and rolling period

GM has a direct relationship with a ship's rolling period. A ship with a small GM will be "tender" - have a long roll period - an excessively low or negative GM increases the risk of a ship capsizing in rough weather (see HMS Captain or the Vasa). It also puts the vessel at risk of potential for large angles of heel if the cargo or ballast shifts (see Cougar Ace). A ship with low GM is less safe if damaged and partially flooded because the lower metacentric height leaves less safety margin. For this reason, maritime regulatory agencies such as the IMO specify minimum safety margins for sea-going vessels. A larger metacentric height, on the other hand can cause a vessel to be too "stiff"; excessive stability is uncomfortable for passengers and crew. This is because the stiff vessel quickly responds to the sea as it attempts to assume the slope of the wave. An overly stiff vessel rolls with a short period and high amplitude which results in high angular acceleration. This increases the risk of damage to the ship as well as the risk cargo may break loose or shift. In contrast a "tender" ship lags behind the motion of the waves and tends to roll at lesser amplitudes. A passenger ship will typically have a long rolling period for comfort, perhaps 12 seconds while a tanker or freighter might have a rolling period of 6 to 8 seconds.

The period of roll can be estimated from the following equation[2]

Where g is the gravitational constant, k is the radius of gyration about the longitudinal axis through the center of gravity and GM is the stability index.

LONGITUDINAL STABILITY AND TRIM

Design Waterline (DWL):

 

The waterline at which the ship is designed to float in the full load condition.

Corresponds to a line in the middle of boot-topping of the ship.

 

Forward Perpendicular (FP):

Aft Perpendicular (AP):

A vertical line drawn at the point of intersection of the DWL and the stem of the ship.

Important in the study of longitudinal stability as well as in frame numbering.

A vertical line drawn at the point of intersection of the DWL and the stern of the ship.

   

Length Between Perpendiculars (LBP):Distance from the FP to the AP.

Found in the DC Book Part 1(a), and/or in the booklet of general plans. When not found there, use the Length Between Draft Marks (LBD) usually found on the Draft Diagram and Functions of Form.

 

Midships Perpendicular (MP):

 

A vertical line intersecting the ship's centerline, half the distance between the FP and AP.

Symbol

Longitudinal Center of Flotation (LCF): Geometric center of the ship's waterline plane. The ship trims about this point.

May be forward or aft of the MP depending on the ship's hull shape at the waterline.

 

 

Center of Flotation Distance:Distance from the LCF to the MP. Found using the Draft Diagram and Functions of Form, as a function of displacement. Used to distribute changes of trim between the fwd and aft drafts.

 

Center of Buoyancy (LCB):

 

The point through which the forces of buoyancy act, longitudinally.

Drag:  

A design feature where the draft aft is greater than the draft forward.

Primarily done to increase propulsion plant effectiveness.

 

Trim:

 

The difference between the forward and after drafts, in excess of design drag.

Parallel Rise/Sinkage (PR/PS):  

When weight is removed/added from/to a ship at LCF, the forward and aft drafts will change by the same amount.

 

Change in Trim (CT):The sum total of the absolute values of the change in forward and after drafts. EXAMPLE:

DFWD DAFT Trim

Original: 20FT 18FT 2FT b/b

Final: 16FT 21FT 5FT b/s

Change: -4FT +3FT 7FT b/s

 

Trimming Arm (TA):The distance from the center of gravity of the weight to the LCF. If the weight is shifted, TA is the distance shifted.

 

Trimming Moment (TM):

Moment about the LCF produced by weight additions, removals, or shifts.

, where w is the amount of weight added, removed, or shifted.

 

Moment to Trim One Inch (MT1"):The moment necessary to produce a change in trim (CT) of one inch. Found using the Draft Diagram and Functions of Form.

 

Tons Per Inch Immersion (TPI):The number of Long Tons added or removed necessary to produce a change in mean draft of one inch. (in salt water)

LONGITUDINAL WEIGHT SHIFTS

When a weight is shifted longitudinally (fore 'n' aft) the net effect on a ship is similar to a see-saw, one end goes up and the other goes down. The pivot of the "see-saw" is located at the Longitudinal Center of Flotation (LCF).

 

 

To calculate the effect of shifting a weight longitudinally on the ship’s drafts, follow these steps:

1. Calculate the Trimming Moment (TM):

2. Calculate the Change in Trim (CT):

3. Calculate the change in forward draft (dFWD):

The + or - sign depends on the location of LCF. If LCF is aft of MP use "+" and if LCF is forward of MP use "-".

4. Calculate the change in aft draft (dAFT):

NOTE: If the weight was shifted forward, dFWD will be positive and dAFT will be negative. If the weight was shifted aft, dAFT will be positive and dFWD will be negative.

Example Problem

The FOWK just completed a transfer of 6500 gallons of diesel fuel (diesel = 322 Gallons/LT). The fuel is now located 135 FT forward of it’s original position. Prior to transfer, the ship’s drafts were 16’9" fwd and 17’3" aft. Design Drag is 0.

LBP is 450 FT, MT1"=825 FT-Tons/inch and LCF is 24 FT aft of MP. The CHENG wants to know the new drafts and trim.

1. Calculate weight of fuel transferred:

 

2. Calculate the trimming moment:

 

3. Calculate the change in trim:

 

4. Calculate the change in forward draft:

 

5. Calculate the change in aft draft:

NOTE: Since the weight was shifted forward, the draft change at the bow is positive, and at the stern is negative.

 

6. Determine the new drafts and trim:

Forward Aft Trim

Original: 16'9.00" 17'3.00" 6.0" b/s

Change: + 1.83" - 1.47" 3.3" b/b

Final: 16'10.83" 17'1.53" 2.7" b/s

 

LONGITUDINAL WEIGHT ADDITIONS AND REMOVALS

When weight is added or removed to/from a ship, the effects on longitudinal stability are evaluated as well. With the weight change, two things will happen:

1. The ship will sink or rise a few inches

2. The ship will trim about the Center of Flotation (LCF)

The easiest way to calculate the draft changes due to a weight addition/removal not located at LCF is to divide the weight change into two steps. First, assume the weight is added at LCF:

 

The added weight causes the entire ship to sink symmetrically in the water. This is called Parallel Sinkage. If the weight was removed, the ship would rise symmetrically out of the water, called Parallel Rise. To calculate the amount each draft changes due to parallel sinkage/parallel rise (PS/PR) use:

 

     

   

     

 

Next, transfer the weight from LCF to it's actual location. Although the weight was never really added at LCF then shifted, the end mathematical result will be the same as when the weight was added directly to it’s actual location.

 

 

This step of moving the weight to it’s actual location is identical to a weight shift problem. Again, to determine the change in the ship’s drafts due to trim:

 

1. Calculate the Trimming Moment (TM):

 

2. Calculate the Change in Trim (CT):

 

3. Calculate the change in forward draft (dFWD):

 

The + or - sign depends on the location of LCF. If LCF is aft of MP use "+" and if LCF is forward of MP use "-".

 

4. Calculate the change in aft draft (dAFT):

 

NOTE: If the weight was shifted forward, dFWD will be positive and dAFT will be negative. If the weight was shifted aft, dAFT will be positive and dFWD will be negative.

 

 

The final step is to calculate the total change in draft forward and draft aft by considering both Parallel Rise/Sinkage and change in trim:

 

Example Problem

During VERTREP, all JP-5 in tanks 5-328-0-J and 5-344-0-J is transferred. The Liquid Loading Report shows 57 LT in these tanks prior to transfer. The center of gravity of the combined tanks is 146 FT aft of MP. The CHENG wants to know the new drafts and new trim of the ship. Design Drag is 1’6" by stern.

LBP = 408FT MT1" = 775 FT-Ton/inch TPI = 32.4 LT/inch

DraftFWD = 14’6" DraftAFT = 15’0" LCF = 24FT aft of MP

 

1. Calculate parallel rise (PR):

 

2. Determine the Trimming Arm (TA):

 

 

3. Calculate the Trimming Moment (TM):

 

4. Calculate the Change in Trim (CT):

 

5. Calculate the change in draft forward due to trim (dFWD):

6. Calculate the change in draft aft due to trim (dAFT):

Since weight was removed aft, this is a forward trimming moment. The forward draft will increase and the stern draft will decrease.

7. Calculate the total change in draft forward (DRAFTFWD):

8. Calculate the total change in draft aft (DRAFTAFT):

9. Calculate the final drafts and ship’s trim:

 FWD Draft AFT Draft Trim

Original: 14’ 6.00" 15’ 0.00" 1’0.00" by the bow

Change: +3.25" -5.72" 8.97" by the bow

New: 14’ 9.25" 14’ 6.28" 1’8.97" by the bow

 

EFFECT OF TRIM ON STABILITY

The Draft Diagram & Functions of Form and Cross Curves of Stability are prepared for ships based on the design condition: No Trim. For most surface ships, so long as trim does not become excessive (more than 1% of the length) these curves are still applicable.

RULES OF THUMB FOR TRIM

     

 1. Maximum acceptable Trim is 1% LBP

 

 2. Follow Liquid Loading Instructions

 

 3. Watch for Hogging and Sagging Stresses

 

     

PLUNGING

Definition: When the Trimming Moment exceeds the Longitudinal Righting Moment, and the ship sinks by the bow or the stern.

Loss of ships by plunging occurs more often in the merchant or auxiliary type ship than in the combatant type, although some destroyers have been lost in this manner. Merchant ships have much larger compartments, and the flooding of these compartments at the bow or stern trims the ship heavily.

TRIM CALCULATION SHEET

It is often desirable to consider the effects of several weights at once when computing draft changes. The Trim Calculation Sheet is a tabular form used to calculate the net trimming moment created by several weight movements.

 

DIRECTIONS FOR USE

 

1. In columns 1 and 2, describe the weight, tank number, flooded compartment, etc. and determine the weight (Long Tons) of each object.

2. Sum total the weights in column 2 to calculate the net weight addition or removal.

3. In column 3, determine the Trimming Arm (TA), the distance from the center of gravity of the weight to the ship’s LCF.

4. In either column 4 or 5, calculate the Trimming Moment by multiplying each weight by it’s Trimming Arm. A weight change causing the bow to sink lower in the water is a forward trimming moment, a weight change causing the stern to sink lower in the water is an aft trimming moment.

5. Sum total the forward trimming moments and aft trimming moments in columns 4 and 5. Take the difference between these totals as the NET Trimming Moment (will either be forward or aft based on the greater column total.)

6. Calculate Parallel Rise or Parallel Sinkage (PR/PS). Divide the net weight addition/removal by Tons per Inch Immersion (TPI, found using Draft Diagram and Functions of Form and ORIGINAL DISPLACEMENT.)

7. Calculate the Change in Trim (CT). Divide the net trimming moment by the Moment to Change Trim by 1" (MT1", found using Draft Diagram and Functions of Form and FINAL DISPLACEMENT.)

8. Calculate the change in draft forward due to trim (dFWD) and change in draft aft due to trim (dAFT) using the equations. If the net trimming moment was forward, dFWD is positive and dAFT is negative. If the net trimming moment is aft, dAFT is positive and dFWD is negative.

9. Fill in the box in the lower right corner by applying all changes to the original conditions.

 

 

EEE) SHIP HANDLING:

1) Anchoring proceduresAssemble tools and look over the side to make sure all is clear2. Turn on power to windlass3. Ease off on the brake for the anchor to be used. The turnbuckle & pelicanhook will catch any slack4. Engage the wildcat and take up tension on the chain5. Back off on the turnbuckle and disconnect pelican hook6. Ease the chain out and stop on the signal of the Mate who will ensure thatthe anchor is eased out enough to allow a free decent when the brake isreleased7. Put the brake on tightly and place the pelican hook on the chain but keep itlazy8. Disengage the wildcat. You are now ready for letting go under controlledconditions9. Upon receiving the command from the bridge to let go, once again checkover the side, ensure that the foredeck is clear and safe when clear, knockthe turnbuckle pelican hook off the chain with the mallet.10. Ease off on the brake and drop the anchor under control to the bottom.Once on the bottom it will be necessary to place some pressure on thebrake so that as the ship eases back, the chain pays out as needed anddoes not pile up upon itself. The Bosun or seaman will call out the shots asthey pass across the deck until the desired length is at the water’s edge oron deck whereupon the brake will be fully engaged, and the turnbuckle or"devils claw" will be placed on the chain to take the strain. Once this isdone, the brake will be eased and all strain removed from the windlass.11. Raise the black ball dayshape or turn on the anchor lights as appropriate12. The foredeck crew informs the bridge and stands by until it is determinedthat the anchor has been set and holding. The Master will set an anchorwatch and the Watch Officer will ensure that the seaman makes periodicchecks of the ground tackle and reports back to the Watch Officer. (to

whom?)13. The anchor watch will take all appropriate measures making use ofavailable equipment to ascertain that the anchor is not dragging, will recordbearings and positions on a regular basis paying special attention tochanges in wind direction and speed and changes in the currents. If it isdetermined that the anchor is dragging, the Master will be notified at onceand the main engine, if not already running and on standby, shall be startedas soon as is safe to do so and made ready. In an emergency, a secondanchor shall be set to minimize dragging. Failing that, any and all measuresavailable such as a tug or other rescue vessel(s) shall be summoned orplaced on standby until the situation is under control. If under the control or direction of port authorities, they must be notified as soon as an adversesituation begins to develop.www.The anchorage and holding groundIn planning the anchorage approach, the Master should consult with thecharts and pilots books as to the suitability of the holding ground of theanchorage, and also with respect to traffic density and ship movements,available swing room, holding ground, protection from the weather, wind,tide and the length of time the vessel is expected to be at anchor.Masters should not just accept the fact that ‘the authorities’ have directedthe vessel to anchor in a particular designated anchorage. There are manydesignated anchorages that are unsuitable in certain conditions,particularly with the onset of heavy weather, closeness to the shoreline,traffic density, exposure to the weather, water depth and/or poor holdingground. If instructed to a designated anchorage, the Master must ascertainfor himself that the anchorage is safe in the prevailing conditions. Mastersshould be prepared to inform the VTS or port authority that the designatedanchorage is not suitable in the prevailing conditions. Amount of cableThe Pasha Bulker , for example was fitted with a standard Admiralty ClassAC14 cast steel high holding power (HHP) anchor. The cable was madefrom the highest-quality grade 3 steel.For an anchor to hold affectively, it is necessary to calculate thecorrect length of cable. There are three commonly used and acceptedguidelines (one shackle of cable is equivalent to 27.5 metres):1) Number of shackles of cable = 1.5√D (D=Depth in metres)2) Length of cables in metres = 6 to 10 x (Depth of water in metres)3) For special steel cable, a formula of:Length of cable used in metres = 39 x√D – where D is the depth ofwater in metres.The ‘scope’ of the cable is the ratio of the length of cable paid out to thedepth of water. The correct scope of the anchor is important if themaximum holding power of the anchor is to be realized, particularly inheavy weather conditions. The anchor holds better when the cable ispulling horizontally to the anchor, and so the Master must be prepared topay out extra cable when conditions such as increased seas, wind,current and tide require the cable pull to remain horizontal.Safety FactorsFIGURE 1: AC14-TYPE ANCHOR FIGURE 2: PROFILE OF ANCHORFIGURE 3: AN ILLUSTRATION OF A SHIP AT ANCHORIn addition to insufficient scope, there is significant yawing or heavypitching, there is a risk that a snatched loading on the cable and anchorwill be applied, and the anchor will be dislodged or will drag, and/or therewill be windlass or cable failure.For example, for a 10,000-15,000 dwt vessel in 20 metres of water, withgood holding ground in sheltered waters, a ‘scope’ of five could be

considered sufficient. Considerations of swinging room, whether thevessel is in ballast/loaded condition and water depth should also be takeninto account. In good weather, in a constrained anchorage with limitedswing room and an expected short stay, less cable could be used;however, increased vigilance, with engines remaining on standby orimmediately available should be considered, depending upon thecircumstances.Anchor holding powerAs quoted in the AMSB Pasha Bulker report, the anchoring equipment isintended for temporarily mooring a vessel within a harbour or shelteredarea when the vessel is waiting for a berth or tide, etc. The equipment istherefore not designed to hold a vessel off fully exposed coasts in roughweather or to stop a ship that is fast-moving or drifting. The type and sizeof the anchoring equipment is based upon the size of vessel and othercriteria. A 25% reduction in anchor weight is allowed, for example, whenhigh holding power anchors (HHP), such as the AC14 type, are providedcableAnchor on sea-bedAn anchor provides maximum holding power when its flukes areembedded in the sea bed. This occurs when the anchor shank lies on thesea bed and the anchor cable pulls horizontally at the anchor shackle.When the pull increases, the cable lying on the sea bed is lifted off,creating a larger angle above the horizontal. As the angle increases, theholding power reduces. As a guide, a pull of 5 degrees above thehorizontal reduces the holding power by 25% and a pull of 15 degreesreduces the holding power by 50%.Therefore to maximise the holding power, the scope of the cable shouldbe sufficient to ensure that, in fair weather, an adequate length of cablewill lie along the sea bed, allowing the cable to pull the anchorhorizontally. When this occurs, the cable rises gently into the hawse pipe.This is why extra cable is paid out when the wind, sea or currentincreases. The curve of the cable, or catenary, absorbs any shock-loadingwhen riding to wind and sea. A catenary is necessary for the cable tohave a horizontal pull on the anchor and ensure maximum holding power.A scope of cable of 10 is considered optimal, while a scope of not lessthan five or six is adequate. Most larger ships are fitted with about 12shackles of cable, approximately 330 metres for each anchor.Consequently, in water depths exceeding 45 metres, the scope of cableachieved is less than six. In depths of up to 35 metres of water, it isimpossible to achieve a scope of 10. However, the cable amount will alsodepend upon length of time expected to stay at the anchorage, weather,holding ground, and swing room.Commercial PressureThere is considerable commercial pressure on Masters. This hasbeen exacerbated in the recent past by many factors, including:• The need for quick turnaround times• Having to be prepared at a moment’s notice when the port advises thata berth is ready• Easy communication access and hence immediate pressure frommanagers / owners / agents / charterers and terminal operators• Having the vessel available to take stores and crew changes• Trying to comply with shore-side instructions when few of thoseissuing the instructions appreciate the scope of problems the Masterhas to contend with, and few are concerned with the safety of the shipor crew.The overriding responsibility of the Master is the safety of his vessel and

crew. Those involved with the technical and commercial management ofvessels should ensure that this responsibility is given their full andunequivocal support. This is possibly the single biggest contribution to thesafety culture of a company and requires the active engagement of seniorcompany managers.It is vital to have a full bridge team available, who know theanchoring plan and maintain a vigilant look out at all times.• Masters must ensure the bridge team is well trained• Masters must seek out advice on ship movements beforeentering congested anchorages, particularly at nightPlanningEvery passage plan should include provision for anchoring. If thisis not done at the commencement of the voyage, the passage planshould be amended when anchoring is known to be a requirement. Itis too late to read the pilot book when the vessel is already yawing30 degrees.• The Master to take charge of the anchoring plan in good time• The Master to pick the time of day and location with due regardto safety of vessel• The Master to consider the abort parameters and contingency planning• Use all the known chart and pilot book information, regarding holdingground, water depths, proximity to shore, dangers, etc.• Use local agent’s information, including designated anchorageareas/restrictions, numbers of vessels at anchor, traffic densityand movements, other local navigational information• Study weather forecasts – not only the immediate weather butseasonal weather patterns• Understand local tides and currents• Take security precautions (for example, anchorages can be in areaswhere piracy is prevalent)• Ensure the bridge team is trained.Example 5 - Congested anchoragesA deep-draft, loaded tanker was proceeding at night to anchor under VTSinstructions. It had planned to anchor at least seven cables away from allother vessels. With a full team on the bridge, it was observed during thefinal approach that five ships were anchored, all on westerly headings.When no more that four cables from the planned anchorage position andat a speed of less than 2 knots, it was noticed that a small cargo vesselhad started to get under way, with initial radar information suggesting acrossing, near-collision course; the vessel was still displaying all deck andanchor lights. Although contact was made with the small vessel by VHF,and the smaller vessel agreed to keep a safe distance, it suddenly choseto alter course very close to the laden tanker’s bow. The Master of thetanker had to order full astern in order to avoid a collision, and the smallvessel passed less than 200 metres ahead.Approaches to congested anchorages are fraught with dangers, evenwhen planned or under competent VTS control. Masters should alwaysconfirm from the VTS before making an anchorage approach if there areany expected ship movements.

C107. Anchoring

1. Test communication equipment..

2. Start the hydraulic motors ( No. 1 & 2 for Stbd Anchor ; No. 2 & 3 for Port Anchor ) 3. Confirm the depth of anchoring position, and determine the length of catenaries anchor chain. 4. Stand by other anchor. 5. Report when anchor is ready. 6. Prepare the black ball (for anchor). 9. In accordance with master’s order, feed the anchor. (“Let go” or “Walk Out”) 10. Report the position/direction/condition of the chain frequently. 11. When anchoring is completed, secure the anchor by using the manual brake & the anchor stopper. 12. Stop hydraulic motors. 13. Report to bridge.

5

Effect of right/left haded propeller when going ahead/astern

Propeller walk is the term for a propeller's tendency to rotate a boat as well as accelerating it forwards or backwards.

A right-handed propeller (which rotates clockwise [as viewed from the stern] when in forward gear) will tend to push the stern of the boat to starboard. When in reverse gear, the effect will be much greater and opposite. A right-handed propeller will now push the aft of the boat to port.

Knowing of and understanding propeller walk is important when maneuvering in small spaces. It can be used to one's advantage while mooring off, or it can complicate a maneuver if the effect works against the pilot.

Propeller walk is a complicated effect which depends on ship geometry, direction of travel, propeller direction, vessel speed and depth of water. Three causes are identified for a vessel in deep water:-

1. Upward oblique flow at the propeller location.2. Vertical wake distribution at the propeller.3. Unbalanced lateral forces on the rudder (when set amidships) arising from the propeller slipstream

impinging on the rudder blade.

The first of these results from there being a measurable difference in speed of water flowing close to the hull and that at lower depths which has not been affected by the vessel's motion. At low speeds the last effect is most pronounced and when going astern has even more influence.

In shallow water the upwards flow from under the vessel becomes much less strong and ultimately disappears. Model tests carried out show that, at a very small under keel clearance, screw bias caused a ship to sheer to starboard (rather than port) when moving ahead and that there is an intermediate depth where the sheer from bias is neither one thing nor the other.

Finally, when moving ahead with the propeller moving astern, flow into and around the propeller is very confused. Generally the overall result for a single screw ship when stopping is a sheer to starboard, but this is not always guaranteed; sometimes it may go the other way, depending often on any yaw rate on the vessel when the propeller starts to turn astern.

Other terms for propeller walk are propeller effect, paddle wheel effect, asymmetric thrust, asymmetric blade effect, or simply prop walk.

m

4) How to maneuver in restricted water, say in a small port

When ships come close to each other, each is apt to feelthe presence of the other. This may manifest itself ina number of ways, ranging from involuntary speedchanges to catastrophic course changes, which may leadto a collision, or grounding. Of course, it is wise to avoidthese sudden, unexpected occurrences by leaving plentyof sea room between ships. However, this is not alwayspossible because ships in a long narrow approach channelhave to pass each other, and some, by the verynature of their work, must be in close proximity to theships they are attending. The hydrodynamic phenomenon which causes ships in close proximity to exhibitthis behavior is known as interaction.The situations in which hydrodynamic interactionsare involved fall into two main categories.— The first concerns ships which are attempting to passone another at very close range, and this is usuallydue to their being confined to a narrow channel.— The second concerns ships which are necessarilymaneuvring in very close proximity for operational

reasons.There are two situations in the first category, i.e., overtakingand head-on encounters. Interaction is mostlikely to prove dangerous when two ships are involvedin close maneuvers. One possible outcome is that theship being overtaken may veer into the path of theother. Another possibility is that when the ships areabeam of one another, the bow of each ship may turnaway from the bow of the other, causing their sterns toswing towards each other. This may be accompanied byan overall strong attractive force between the two shipsdue to the reduced pressure between the underwaterportions of the hulls. In a head-on encounter, the interactionis less likely to have a dangerous effect as generallythe bows of the two ships will tend to repel eachother as they approach. In the second category, whereships are maneuvring at close quarters for operationalreasons, there is potential danger when one of the shipsis larger than the other, and this most commonly occursin normal service operations when a ship is being attendedby a tug, and also in mid-sea replenishments ofships.In the restricted waters of short sea shipping routes inparticular, the maneuvring and course-keeping of shipsmay be affected by interactions between the ship andthe boundaries of the navigation area.

5) Turning circleShip’s  Characteristics Fundamentals  of  Before  we  can  discuss  the  techniques  used to  steer  a  ship,  you’ll  have  to Shiphandling learn  the  basics  of  shiphandling.  Use the  following  table  and  figure 11-5  to  learn  the  terms  associated  with  a  ship’s characteristics. Term Pivot Point Definition A  ship’s  pivot  point  is  a  point  on  the centerline  about  which  the ship  turns  when  the  rudder  is  put  over.  The  pivot  point scribes  the ship’s  turning  circle. Turning  Circle A  ship’s  pivot  point  is  nearly always  located  about  one-third  the ship’s  length  from  her  bow  when  moving ahead,  and  at  or  near  her stern  when  moving  astern.  The location of the pivot  point will vary  with  ship’s  speed.  An  increase  in  speed  will  shift  the  pivot point  in  the direction  of  the  ship’s  movement. A  ship’s  turning  circle  is  the  path  followed  by the  ship’s  pivot point  when  making  a  360  degree  turn.  The  diameter  of  the turning circle  varies  with  rudder  angle  and  speed.  With  constant  rudder angle,  an increase  in  speed  results  in  an  increased  turning  circle. Very  low  speed  (those approaching  bare  steerageway)  also increases  the  turning  circle  because  of  reduced rudder  effect. Advance, Transfer, Tactical  Diameter, Final  Diameter. Knowledge  of the  turning  characteristics  of  one’s  ship  is  essential to  safe  shiphandling, particularly  when  in  restricted  waters. Advance  is  the  amount  of  distance  run  on the  original  course  until the  ship  steadies  on  the  new  course.  Advance  is  measured from  the point  where  the  rudder  is  first  put  over. Transfer  is  the  amount  of distance  gained  towards  the  new  courseTactical  diameter  is  the  distance  gained  to  the  left  or  right  of  the original  course after  a  turn  of  180°  is  completed. Final  diameter  is  the  distance  perpendicular  to the  original  course measured  from  the  180°  point  through  360°.  If  the  ship

continued to  turn  at  the  same  speed  and  rudder  indefinitely,  it  would  turn  on this circle.  The  final  diameter  is  almost  always  less  than  the tactical  diameter

MOB procedure

MAN-OVERBOARD SIGNAL 7. In formation, the officer in tactical command (OTC) of all ships present is notified. The  man-overboard  flag  is  the  OSCAR  flag displayed at the foretruck or where it can best be seen during daylight hours. When someone goes overboard at night, the peacetime procedure is the display of two blinking red lights arranged vertically. In addition, either by day or night, the ship losing the person sounds six or more short blasts on the whistle. Man-Overboard Procedure Only the ship losing a person overboard may make the signals described in the foregoing section. Action taken by other ships in a formation or around the ship losing  the  person  overboard  depends  on  existing conditions. If at all possible, the person overboard is to be rescued, but collisions must be avoided. Flag or Blinker Pyrotechnics Meaning 8 1 white star Steer  straight away from ship 8  PORT 1 red star Steer left (or to port) 8 STARBOARD   1 green star Steer  right (or  to  starboard) The peacetime (standard) practice for a ship losing a person overboard follows: 1. Anyone aboard ship who sees a person fall overboard must shout as loud as possible and without  hesitation,  “MAN  OVERBOARD, STARBOARD  (PORT)  SIDE.”  This call  must be repeated until the conning officer takes necessary action or indicates in some way that the word was received. 8 SCREEN QUEBEC 2  green  stars Steer  straight toward ship 2 red stars Return to ship 2  white  stars Steady  on present  course Lifeboat Signal to Ship When a lifeboat is attempting to pick up a person overboard at night, the following signals are used from the boat to the ship. 2. Rudder and engines are used, if appropriate, to avoid hitting the person with the screws. 3.   A  lifebuoy  and  smoke float  are  dropped. When launching a Mk 6 smoke float, (a) remove the tape from over the pull ring, (b) pull the ring smartly from the device, and (c) immediately throw the smoke float over the side. Do NOT remove the tape from over the pull ring until just before launching. Salt air will rust the pull wire, causing it to break and thereby making the device  useless. Visual  Signals Pyrotechnics Blinker  or 1 green star semaphore 1 white star 1 redstar Meaning Cannot  find person Have  recovered person Need  assistance SUMMARY 4. At least six short blasts are sounded on the whistle. 5.   By day the OSCAR flag is hoisted where it can be seen best. By night, two pulsating red lights arranged  vertically  are  displayed.  (In peacetime any ship may use searchlights as necessary.) You should have learned in this chapter the various watchstander's  equipment  used  on  the  ship's  bridge. Failure to use proper nomenclature or a lack of basic knowledge of a ship's equipment is unprofessional and may, in an emergency, lead to dangerous confusion. As an underway watchstander, you will perform, on occasion, routine checks or tests on bridge equipment as either the messenger of the watch or the helmsman. 6.  The  ship  is  maneuvered  as prescribed  by Know your job and keep your equipment in good doctrine. working order so you can do an outstanding job! Signals to Lifeboat The following signals are used to direct a lifeboat engaged  in  picking up  a  person  overboard.

7) SQUAT

Ship squat can be caused in two ways. On most occasions squat is caused by the forward motion of a vessel. 0Squat is the decrease in underkeel clearance caused by this forward motion. ' As the ship moves forward she develops a mean bodily sinkage together with a slight trimming effect. The algebraic sum of bodily sinkage and the trim ratio (forward or aft) is known as "ship squat". It must be emphasised that for any draught, squat is NOT the difference in reading between the situation when a vessel is stationary and when she is underway. This mis-conception is inaccurate and misleading.

For example, the difference in bow draught readings due to forward motion (1)might be 2m, whilst the decrease in underkeel clearance might only be 040m.

The main factors affecting ship squat are:— the forward speed V which is the speed of the ship over the ground. This is K2 the most important factor because ship squat varies directly as V . If the Kspeed is halved then the squat is quartered. the block co-efficient C . This also is important. Squat varies directly with Bthe C . In other words, oil tankers and OBOs will have comparitively more Bsquat than passenger liners and container ships. This is shown graphically in figure 3. the relationship between the depth of water (H) and the static mean draughtof the ship (T). In my research I particularly considered measured squats forH H/ range of 1.10 to 1.40. As / decreases, squats increase. T Tthe presence of river or canal banks. The closer banks are to the sides of a (8)moving vessel, the greater will be the squats. (9) the presence of another ship in a river in a crossing or passing manoeuvre.The presence of the second ship increases the squats on both vessels.

UKC / Minimum required UKC

Under-keel clearance means the minimum clearance available between the deepestpoint on the vessel and the bottom in still water. Masters and pilots shall apply a plus or minusallowance for the tideUKC NYK StandardOut of Harbour Limit : 15.0% of DraftWithin Harbour Limit : 10.0% of Draft

FFF) RADAR / ARPA

1) Define / Explain: Super/Sub refraction, ducting - which phenomena isgood / bad for vessel

Subrefraction -- The bending of the radar beam in the vertical which is less than under standard refractive conditions. This causes the beam to be higher than indicated, and lead to the underestimation SUPERREFRACTION.— If  the  atmosphere’s temperature  increases  with  height (inversion)  and/or the water vapor content decreases rapidly with height, the  refractivity gradient  will  decrease  from  the standard  (table  2-1).  This  situation  is  known  as superrefraction, and causes the radar beam to deflect earthward below its normal path (fig. 2-15, view C). Generally,   radar   ranges   are   extended   when superrefractive conditions  exist.  However,  some targets may appear higher on radar than they would under standard    atmospheric conditions.

Atmospheric ducting is a mode of propagation of electromagnetic radiation, usually in the lower layers of Earth’s atmosphere, where the waves are bent by atmospheric refraction.[2] In over-the-horizon radar, ducting causes part of the radiated and target-reflection energy of a radar system to be guided over distances far greater than the normal radar range. It also causes long distance propagation of radio signals in bands that would normally be limited to line of sight.

Normally radio "ground waves" propagate along the surface as creeping waves. That is, they are only diffracted around the curvature of the earth. This is one reason that early long distance radio communication used long wavelengths. The best known exception is that HF (3–30 MHz.) waves are reflected by the ionosphere.

The reduced refractive index due to lower densities at the higher altitudes in the Earth's atmosphere bends the signals back toward the Earth. Signals in a higher refractive index layer, i.e., duct, tend to remain in that layer because of the reflection and refraction encountered at the boundary with a lower refractive index material. In some weather conditions, such as inversion layers, density changes so rapidly that waves are guided around the curvature of the earth at constant altitude.

Phenomena of atmospheric optics related to atmospheric ducting include the green flash, Fata Morgana, superior mirage, mock mirage of astronomical objects and the Novaya Zemlya effect

2) Different causes of radar false echoSometimes echoes are displayed on the screen in positions where no genuine targets exists.1- Indirect echoes (reflected echoes)These can occur when radar energy is deflected in the direction of an object by some obstructions in the path of the radiated energy, either on board the ship or ashore. The returning energy follows a reciprocal path and so causes an echo to be displayed in the direction of the obstructionWhere echoes are suspected of being false, they should be assumed to be real until proved false beyond all reasonable doubt.

False echoes from bridges

2Multiple echoes

multiple echoes are likely when a target is close and energy bounces back and forth between the hulls of the target and the observing ship, with some of the energy entering the antenna at each return (Figure 3.59). The features of this form of response are that the echoes: a) Lie along a single direction. b) Are consistently spaced.

Side echoes:

Side echoes are again associated with targets that are at close range and result from the radar beam being surrounded by smaller beams or lobes. Some of the echoes will appear to be separate but all will be at the same range, i.e. as if all were lying on the same range circle. This phenomenon is generally associated with smaller antennae and those which are dirty or damaged.

–Radar - to - radar interference

All civil marine radar systems are required to operate within a fairly narrow slot of approximately 200 MHz allocated in the X-band or S-band. When it is considered that the receiver bandwidth of a marine radar system may be as much as 20 MHz, and given the high power and antenna height of a shipboard system, it is obvious that, except in mid-ocean, there is a very high probability of receiving interfering radiation from other vessels in the vicinity which are operating radar equipment. If the radiation received is within the limits of the receiver bandwidth the signals will be amplified in the same way as those reflected from targets and will produce a visible response on the display.

5- Second trace echoes.Under conditions of extra –refraction the radar energy follows closely the surface of the Earth and travels to greater distances than under standart conditions. This means that echoes from distant targets can arrive back at the receiver one trace late. (i.e. on the second trace) or even later, be accepted by the receiver and so be displayed but obviously at an incorrect range.

6- False echoes from power cablesIt has for some time been recognized that electromagnetic waves can react with the electromagnetic field surrounding a cable carrying a current in such a way that a false echo appears on the radar display. The false echo so produced will appear in the direction of the perpendicular from the vessel to the power cable and at the range of the cable (Figure 3.67). Unfortunately the actual power cable itself does not produce a response and so it can be very difficult to associate the observed echo with the cable and thereby have some indication that the echo may be false. Where

- the cable is at right angles to the channel, the false echo will appear in the channel so that, however the vessel maneuvers in the channel to avoid it, the false echo will always move into the vessel's path.

- Where the cable is angled across the waterway, the false echo may initially appear among the shore echoes and so go unnoticed, but as the vessel approaches the cable, the false echo will appear on the water as if from a vessel on a converging course.

- Consider the situations illustrated in Figures 3.67(b) and 3.67(c). As the vessel approaches the cable, a 'vessel' would appear to put out from the starboard bank and proceed on a collision course. Any attempt by the observing vessel to pass under the 'stern' of the false echo would cause the false echo to return toward the bank, i.e. again into the vessel's path. If the observing vessel stopped, the 'target' would also appear to stop.

- In Figure 3.67(c), the false echo would put out from the port bank, again on a collision course. Here the logical maneuver would be for the observing vessel to move farther over to the starboard side of the channel. The false echo would continue to crowd the observing vessel into the starboard bank. The result of stopping or a port maneuver would be as described above. On some waterways, power cables have had radar reflectors fitted to them in order that their line will appear on the radar display. The unusual behavior of echoes in the vicinity of the cable may thus be associated with the cable and should be treated with due caution.

3) Minimum acquisition capacity of ARPA (IMO Standard)

4) Different causes of ARPA alarms

There are six main situations which cause the ARP to trigger visual and audiblealarms:Collision alarmGuard zone alarmLost target alarmTarget full alarm for manual acquisitionTarget full alarm for automatic acquisitionSystem failure

GGG) GPS / DGPS

1) Principles of GPS/DGPS

Differential GPS (DGPS) is a land-based technology that works to improve the accuracy of GPS navigation. Differential GPS improves the accuracy to within two meters of the actual position for moving objects and even better for stationary situations. Differential GPS takes GPS to a much higher level- it becomes a tool for positioning things on a precise scale. 

How it Works

Differential GPS works through two receivers one of which is stationary and the other moving around making position measurements. Here is the underlying principle. GPS receivers calculate distances by using the time signals take to travel from satellites. This work needs signals from at least four satellites. Each of these signals has some errors due to different factors like disturbances in the atmosphere. These errors can have a cumulative effect in the final result the GPS gets. However the satellites are so far away in space, the distances we travel on earth are pretty insignificant in comparison. This way the signals two receivers within a distance of a few hundred kilometers receive have the

same amount of errors, as they have traveled the same amount of distance in atmosphere. This is the principle put to use in DGPS. The stationary (reference) receiver is placed at a point that has been very accurately marked and surveyed. This station is considered to receive the same GPS signals with the same amount of error as the moving receiver. The stationary receiver then works backwards on the equation. This means that instead of using timing signals to work out its position, it uses its already measured position to calculate timing. It then compares how long the signals should take to travel with the actual time they took to reach the station. The difference in the two readings gives the error component which is common to it and the moving receiver. The stationary receiver repeats this process for all the visible satellites, encodes the information into a standard format and then relays the information to the moving receiver. The moving receiver is thus able to make appropriate corrections. Error Transmissions- the nitty-gritty DGPS receivers cannot transmit the corrections on their own, but use attached radio transmitters for the corrections. The moving receiver gets a complete list of errors, meaning errors with reference to each satellite, and applies whichever data is applicable to them. Limits Differential GPS can eliminate only those errors that are common to both the stationary and moving receivers. This does not include multi-path errors (these are errors that happen due to the signals reflecting off objects like mountains, tall buildings and dense foliage), as these are happening very close to the receiver. Further, DGPS cannot account for any internal errors within an individual receiver.

2) Number / height of satellites od 24 do 31 – 20200 km

As of March 2008,[28] there are 31 actively broadcasting satellites in the GPS constellation, and two older, retired from active service satellites kept in the constellation as orbital spares. About ten satellites are visible from any point on the ground at any one time

3) Minimum number of satellites to obtain fix-3

4) Accuracy of GPS / DGPS (error in meter)

(intentional error) was turned off (based on DePriest's navigation and GPS articles, see references)

Source of errorAmount of error

(meters)

Ionosphere 4

Clock 2.1

Ephemeris 2.1

Troposphere 0.7

GPS receiver 0.5

Multipath 1

Total 10.4

DGPS Beacon CorrectionsThe U.S. Coast Guard has installed two control centers and more than 60 beacon stations along the coastal waterways and in the interior United States to transmit DGPS correction data that can improve GPS accuracy. The beacon stations use marine radio beacon frequencies to transmit correction data to the remote GPS receiver. The correction data typically provides 1- to 5-meter accuracy in real time.

In principle, this process is quite simple. A GPS receiver normally calculates its position by measuring the time it takes for a signal from a satellite to reach its position. Because the GPS receiver knows exactly where the satellite is, how long the satellite took to send the signal, and the signal’s speed, the receiver can compute what is called a pseudorange (distance) to the satellite. This distance must be corrected before the GPS receiver uses it to compute its final position.

A DGPS beacon transmitter site has a reference GPS receiver (or base station) located on a point that’s been surveyed very accurately. The reference receiver receives the same GPS signals as other receivers, but because its location is known so precisely, it can attack the equations backwards, using timing signals to calculate its position correction. The reference receiver figures out how long the GPS signals should have taken to reach it and compares that time with the signals’ actual travel time. The difference is an error correction factor. Once the error correction factor has been computed, the beacon station sends it to the field GPS receiver (or rover), which uses it to compute a more accurate location.

Beacon transmitters operate in the 300 kHz frequency band and send data at a rate of either 100 or 200 bits per second, depending on the station. Because the station must calculate the corrections and transmit them, the receiver may apply the corrections 2 to 5 seconds after they were made. Most errors change slowly, so this delay usually is not a problem. The accuracy of such systems depends somewhat on how close the receiver is to the beacon, but can be within 1 to 5 meters overall. The rule of thumb is that the error will increase 1 meter for every 160 kilometers the receiver is from the beacon station.

HH) DRILL

1) Different types of drills: weekly, monthly, quarterly

2) Procedures - MOBMOB procedure

MAN-OVERBOARD SIGNAL 7. In formation, the officer in tactical command (OTC) of all ships present is notified. The  man-overboard  flag  is  the  OSCAR  flag displayed at the foretruck or where it can best be seen during daylight hours. When someone goes overboard at night, the peacetime procedure is the display of two blinking red lights arranged vertically. In addition, either by day or night, the ship losing the person sounds six or more short blasts on the whistle. Man-Overboard Procedure Only the ship losing a person overboard may make the signals described in the foregoing section. Action taken by other ships in a formation or around the ship losing  the  person  overboard  depends  on  existing conditions. If at all possible, the person overboard is to be rescued, but collisions must be avoided. Flag or Blinker Pyrotechnics Meaning 8 1 white star Steer  straight away from ship 8  PORT 1 red star Steer left (or to port) 8 STARBOARD   1 green star Steer  right (or  to  starboard) The peacetime (standard) practice for a ship losing a person overboard follows: 1. Anyone aboard ship who sees a person fall overboard must shout as loud as possible and without  hesitation,  “MAN  OVERBOARD, STARBOARD  (PORT)  SIDE.”  This call  must be repeated until the conning officer takes necessary action or indicates in some way that the word was received. 8 SCREEN QUEBEC 2  green  stars Steer  straight toward ship 2 red stars Return to ship 2  white  stars Steady  on present  course Lifeboat Signal to Ship When a lifeboat is attempting to pick up a person overboard at night, the following signals are used from the boat to the ship. 2. Rudder and engines are used, if appropriate, to avoid hitting the person with the screws. 3.   A  lifebuoy  and  smoke float  are  dropped. When launching a Mk 6 smoke float, (a) remove the tape from over the pull ring, (b) pull the ring smartly from the device, and (c) immediately throw the smoke float over the side. Do NOT remove the tape from over the pull ring until just before launching. Salt air will rust the pull wire, causing it to break and thereby making the device  useless. Visual  Signals Pyrotechnics Blinker  or 1 green star semaphore 1 white star 1 redstar Meaning Cannot  find person Have  recovered person Need  assistance SUMMARY 4. At least six short blasts are sounded on the whistle. 5.   By day the OSCAR flag is hoisted where it can be seen best. By night, two pulsating red lights arranged  vertically  are  displayed.  (In peacetime any ship may use searchlights as necessary.) You should have learned in this chapter the various watchstander's  equipment  used  on  the  ship's  bridge. Failure to use proper nomenclature or a lack of basic knowledge of a ship's equipment is unprofessional and may, in an emergency, lead to dangerous confusion. As an underway watchstander, you will perform, on occasion, routine checks or tests on bridge equipment as either the messenger of the watch or the helmsman. 6.  The  ship  is  maneuvered  as prescribed  by Know your job and keep your equipment in good doctrine. working order so you can do an outstanding job! Signals to Lifeboat The following signals are used to direct a lifeboat engaged  in  picking up  a  person  overboard.

III) METEOROLOGY

1) Movement of storm in N.H./S.H.

FIGURE 144. Principal regions where tropical cyclones form and their favored directions of movement.

Movement

Tropical cyclones in the Northern Hemisphere usually move in a direction between west and northwest while in low latitudes. As these storms move toward the midlatitudes, they come under the influence of the prevailing westerlies. At this time the storms are under the influence of two wind systems, i.e., the trade winds at low levels and prevailing westerlies aloft. Thus a storm may move very erratically and may even reverse course, or circle. Finally, the prevailing westerlies gain control and the storm recurves toward the north, then to the northeast, and finally to the east-northeast. By this time the storm is well into midlatitudes.

2) Safe Maneuvers in dangerous semi-circle in N.H./S.H.

dangerous semicircle—The side of a tropical cyclone to the right of the direction of movement of the storm in the Northern Hemisphere (to the left in the Southern Hemisphere), where the winds are stronger because the cyclone's translation speed and rotational wind field are additive.

The opposite side is termed the navigable semicircle. This terminology originated in the days of sailing ships. It occurred naturally since 1) the dangerous semicircle of the storm has the strongest winds and heaviest seas; 2) a sailing ship on this side tends to be carried into the path of the storm; and 3) if the storm recurves, its center is likely to cross the course of a ship running before the wind.

3) Pressure and wind belts

Wind Belts

The general circulation of winds arises from the global redistribution of heat from warm low latitudes to cold high latitudes, driven by the development of surface pressure gradients. Wind blows from high to low pressure regions, although airflow is deflected by the Coriolis force as a result of the Earth's rotation, and tends to follow more east-west trends rather than north-south trends.

Air movement at or near the equator is light. At sea the region became known to sailors as the Doldrums. Air from the subtropical zones in the Northern and Southern Hemispheres converges here in a zone called the Inter-Tropical Convergence Zone (ITCZ). These low latitude wind belts became known as the Northeast and Southeast Trades, which merchant ships used to cross the Atlantic Ocean from Europe to the New World. In the Indian Ocean, Northeast Trade winds blow throughout the winter months. During the Northern Hemisphere summer however, the ITCZ is shifted well to the north of the equator, when the midday Sun is overhead at the Tropic of Cancer at latitude 23.5° north. The Southeast Trade winds now cross the equator, and are deflected to the right by the Coriolis force, forming the Southwest Monsoons. This summertime airflow picks up considerable moisture crossing the Indian Ocean, and brings a heavy and prolonged wet season to India and Southeast Asia through April to September, known as the Monsoon.

The temperate mid-latitudes are influenced by a stream of westerly airflow. In the Northern Hemisphere the winds became known as the Southwest Antitrades, which prevail for much of the year. In the Atlantic, the Gulf Stream enhances the warmth of the southwesterly air masses, which influence the mild weather of the UK and Western Europe. This warm flow of air collides with the Polar Easterlies from the Arctic region, generating a zone of cyclonic low pressure, where frontal depressions frequently form. In the Southern Hemisphere, the westerlies are known as the Roaring Forties, which blow more or less continuously around the Earth due to the absence of significant landmasses.

JJJ) SURFACE CURRENT

1) Speed of Kurushio current

KUROSHIO CURRENTThe Kuroshio (Black) Current is the biggest western boundary surface current in the western Pacific. Because of its high speed (2.7-3.6 km/hr), great thickness (1.0 km) and width (150-200 km), and high temperature (28°-29°C in summer and 22°-25°C in winter), it plays an important role in the meridional transport of heat, mass, momentum, and moisture from the western Pacific warm pool to high latitudes in the north Pacific.

The Kuroshio Current is narrow and fast-moving. It is 80 km (50 mi) wide and reaches speeds of 3.5 knots.

2) Effect of K.C. when navigating from Taiwan or vice versa

3) Measures to counter act K.C. when sailing from Tokyo to Taiwan

1) What Master will do in case vessel in distress?

It is the master who decides when his vessel is in distress and in need of assistance. If the master decides that his vessel needs salvage services, it is the duty of all other parties involved to assist the master in his efforts to save, the vessel and find the best available means to secure the safety of, the vessel.

 

 When a master has accepted services from a salvor on either fixed terms or particularly if the services are performed under an open form contract, it is very important that the master and the crew keep a close record of what the salvors actually perform and under what circumstances. Although the crew and the salvors will represent two different sides in an arbitration, all salvage agreements, including the LOF, require full co-operation between the crew of the salved vessel and the salvors. To illustrate how an arbitrator will assess the salvors’ performance in an arbitration, we will list below the “criteria for fixing the reward” as set out in the LOF.

 

1.     The salved value of the vessel and other property;2.     The skill and efforts of the salvors in preventing or

minimising damage to the environment;3.     The measure of success obtained by the salvor;4.     The nature and degree of danger;5.     The skill and efforts of the salvors in salving the 

vessel, other property and life;6.     The time used and expenses and losses incurred

by the salvors;7.     The risk of liability and other risks run by the

salvors or their equipment;8.     The promptness of the services rendered;9.     The availability and use of vessels or other

equipment intended for salvage operations;

10.   The state of readiness and efficiency of the salvors’ equipment and the value thereof.

SOLAS Chapter V contains, for instance, the obligation on a master to communicate danger messages by all means at his disposal and, on receiving a signal that persons are in distress at sea, to proceed with all speed to their assistance.Marine Rescue and Co-ordination Centres (MRCC) SAR (Search And Rescue) operations would be much more efficient if they had all the rescue craft fitted with AIS, to quickly determine which ship is closest to a distress situation. During a search, all the crafts could be tracked and plotted, enabling the MRCC to monitor the progress, to direct the available resources efficiently and to ascertain that search coverage is without gaps. Furthermore, if a ship in distress had an AIS, it could be seen on displays of all the surrounding ships and also at the MRCC.

2) Why the Master will stay on board?

3) What is pillar?A pillar is a stone cylinder supporting a portion of a building. An example can be seen in the US Capital building.

In a broader sense, the term "pillar" is used to describe anything that provides major structural support. So the part of a microscope that holds the lenses rigidly in place is called a "pillar" even though it is not made of stone and is not supporting any part of a building.

The term is also used metaphorically to describe core elements, as, for example, in the "Five Pillars of Islam."

4) Shear force?shear stress, denoted (tau), is defined as a stress which is applied parallel or tangential to a face of a material, as opposed to a normal stress which is applied perpendicularly

5) What is doldrums?

The Doldrums, also called the "equatorial calms", is a nautical term for the equatorial trough, with special reference to the light and variable nature of the winds.[1] It affects areas of the Atlantic Ocean, the Pacific Ocean and the Indian Ocean that are within the Intertropical Convergence Zone, a low-pressure area around the equator, where the prevailing winds are calm. The low pressure is caused by the heat at the equator, which makes the air rise and travel north and south high in the atmosphere, until it subsides again in the horse latitudes. Some of that air returns to the Doldrums through the trade winds. This process can lead to light or variable winds and more severe weather, in the form of heavy squalls, thunderstorms and hurricanes.

6) Whistle signal when near land and response of other vessel?

7) Pilot boat lights?white light over a red light at night

8) How to correct negative GM?Lower Center of Gravity. (i.e. shifting heavy weights to a lower position)Top up empty tanks to minimize free surface effect.Load additional double bottom tanks to lower center of gravity.

9) What is the use of hydrostatic tables and what is hydrostatic curve?

Hydrostatic information is usually supplied to ship officer in form of the table or a graph. Various items of hydrostatic information are plotted against draft. When information is required for specific draft, first locate the draft on the scale on left side on the left hand margin on the figure. Then draw horizontal line trough the draft to cut all of the curves on the figure. Next draw perpendicular trough intersection of this line with each of the curves in turn and read off the information from the appropriate scale

10) What are special vessels?Dredgers Tug & workboatsSpecial service vessels (research vessels, ice breakers, cable layers etc.)Fishing vesselsInland navigationRESEARCH & SEISMIC VESSEL AND WORKBOATS PILOT & PATROL / GUARD & RESCUE VESSELSCRANE VESSEL & HEAVY LIFT VESSELSOIL POLUTION VESSELSBUOY & LIGHTHOUS VESSELS

11) Anchoring procedure?

) Anchoring proceduresAssemble tools and look over the side to make sure all is clear2. Turn on power to windlass3. Ease off on the brake for the anchor to be used. The turnbuckle & pelicanhook will catch any slack4. Engage the wildcat and take up tension on the chain5. Back off on the turnbuckle and disconnect pelican hook6. Ease the chain out and stop on the signal of the Mate who will ensure thatthe anchor is eased out enough to allow a free decent when the brake isreleased7. Put the brake on tightly and place the pelican hook on the chain but keep itlazy8. Disengage the wildcat. You are now ready for letting go under controlledconditions9. Upon receiving the command from the bridge to let go, once again checkover the side, ensure that the foredeck is clear and safe when clear, knockthe turnbuckle pelican hook off the chain with the mallet.10. Ease off on the brake and drop the anchor under control to the bottom.Once on the bottom it will be necessary to place some pressure on the

brake so that as the ship eases back, the chain pays out as needed anddoes not pile up upon itself. The Bosun or seaman will call out the shots asthey pass across the deck until the desired length is at the water’s edge oron deck whereupon the brake will be fully engaged, and the turnbuckle or"devils claw" will be placed on the chain to take the strain. Once this isdone, the brake will be eased and all strain removed from the windlass.11. Raise the black ball dayshape or turn on the anchor lights as appropriate12. The foredeck crew informs the bridge and stands by until it is determinedthat the anchor has been set and holding. The Master will set an anchorwatch and the Watch Officer will ensure that the seaman makes periodicchecks of the ground tackle and reports back to the Watch Officer. (towhom?)13. The anchor watch will take all appropriate measures making use ofavailable equipment to ascertain that the anchor is not dragging, will recordbearings and positions on a regular basis paying special attention tochanges in wind direction and speed and changes in the currents. If it isdetermined that the anchor is dragging, the Master will be notified at onceand the main engine, if not already running and on standby, shall be startedas soon as is safe to do so and made ready. In an emergency, a secondanchor shall be set to minimize dragging. Failing that, any and all measuresavailable such as a tug or other rescue vessel(s) shall be summoned

12) Gyro error?(navigation) The error in the reading of the gyro compass, expressed in degrees east or west to indicate the direction in which the axis of the compass is offset from the north.

13) Ports restricted at night?????????????’

14) Counter equatorial current?

The Equatorial Counter Current is a significant ocean current in the Pacific and Indian Oceans that flows west-to-east at approximately five degrees north. The Counter Currents result from balancing the westward flow of water in each ocean by the North and South Equatorial currents.

In El Niño years, this current intensifies in the Pacific Ocean

current phenomenon noted near the equator, an eastward flow of oceanic water in opposition to and flanked by the westward equatorial currents of the Atlantic, Pacific, and Indian oceans. Lying primarily between latitude 3° and 10° N, the countercurrents shift south during the northern winter and north during the summer. To either side the trade winds blow constantly and push great volumes of water westward in the equatorial currents, raising the sea level in the west. Within the doldrums, where strong constant winds are absent, the higher western sea levels flow downslope to the east. The Pacific Equatorial Countercurrent is very strong and is definable year-round. The Atlantic Equatorial Countercurrent is strongest off the coast of Ghana (Africa), where it is known

as the Guinea Current. The countercurrent of the Indian Ocean flows only during the northern winter and only south of the equator.

15) Bank effect?

Bank effect refers to the tendency of the stern of a ship to swing toward the near bank when operating in a river or constricted waterway.

The asymmetric flow around a ship induced by the vicinity of banks causes pressure differences (Bernoulli's principle) between port and starboard sides. As a result, a lateral force will act on the ship, mostly directed towards the closest bank, as well as a yawing moment pushing her bow towards the centre of the waterway. The squat increases due to the decreased blockage.

This phenomenon depends on many parameters, such as bank shape, water depth, ship-bank distance, ship properties, ship speed and propeller action. A reliable estimation of bank effects is important for determining the limiting conditions in which a ship can safely navigate a waterway.

This phenomenon has several different names, including bank suction, stern suction, and ship-bank interaction.

16) NUC/Restricted?

Vessels Not Under Command or Restricted in Their Ability to Maneuver (a) A vessel not under command shall exhibit: (i) two all-round red lights in a vertical line where they can best be seen; (ii) two balls or similar shapes in a vertical line where they can best be seen; (iii) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight

(b) A vessel restricted in her ability to maneuver, except a vessel engaged n mineclearance operations, shall exhibit: (i) three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white; (ii) three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond; (iii) when making way through the water, a masthead light or lights, sidelights and a sternlight, in addition to the lights prescribed in subparagraph (i); (iv) when at anchor, in addition to the lights or shapes prescribed in subparagraphs (i) and (ii), the light, lights or shape prescribed in Rule 30.

Vessel restricted in her ability to maneuver—making way; vessel less than 50 meters in length.

(c) A power-driven vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course shall, in addition to the lights or shapes prescribed in Rule 24(a), exhibit the lights or shapes prescribed in subparagraphs (b)(i) and (ii) of this Rule.

17) Poor stability?

Too high value of KG result in poor stability at larger angels no matter what practical form changes are made. A slow roll period is index of poor stability.

Required stabilityIn order to be acceptable to classification societies such as the American Bureau of Shipping, Lloyd's Register of Ships, and Det Norske Veritas, the blueprints of the ship must be provided for independent review by the classification society. Calculations must also be provided which follow a structure outlined in the regulations for the country in which the ship intends to be flagged.

For U.S. flagged vessels, blueprints and stability calculations are checked against the U.S. Code of Federal Regulations (CFR) and SOLAS conventions. Ships are required to be stable in the conditions to which they are designed for, in both undamaged and

damaged states. The extent of damage required to design for is included in the regulations. The assumed hole is calculated as fractions of the length and breadth of the vessel, and is to be placed in the area of the ship where it would cause the most damage to vessel stability.

In addition, U.S. Coast Guard rules apply to vessels operating in U.S. ports and in U.S. waters. Generally these Coast Guard rules concern a minimum metacentric height or a minimum righting moment.

18) Pilot chart?

Pilot Charts depict averages in prevailing winds and currents, air and sea temperatures, wave heights, ice limits, visibility, barometric pressure, and weather conditions at different times of the year. The information used to compile these averages was obtained from oceanographic and meteorologic observations over many decades during the late 18th and 19th centuries.

The Atlas of Pilot Charts set is comprised of five volumes, each covering a specific geographic region. Each volume is an atlas of twelve pilot charts, each depicting the observed conditions for a particular month of any given year.

The charts are intended to aid the navigator in selecting the fastest and safest routes with regards to the expected weather and ocean conditions. The charts are not intended to be used for navigation.

19) Cofferdam?

(nautical) an empty space that acts as a protective barrier between two floors or bulkheads on a ship

20) Civil, nautical, astronomical twightlight?

Definitions

Various definitions of twilight.

Twilight is defined according to the position of the sun (its centre) relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (brightest), nautical twilight and astronomical twilight (darkest).

Definition Position of sun

Night more than 18°Astronomical twilight 12 – 18°Nautical twilight 6 – 12°Civil twilight less than 6°Day (sun above the horizon)

For comparison, the angular diameter of the sun is 0.5°.

Note that if the sun is 8½ degrees below the horizon, it provides the same level of illumination to the surface of the Earth as a full moon directly overhead.

(For these definitions, an ideal horizon 90° from the zenith is used. The altitudes of the sun below the horizon are "true geometric" altitudes; that is, refraction by the atmosphere and other small factors influencing the experiential position of the sun are not to be accounted for.)

21) Fog signals?Sound Signals in Restricted Visibility In or near an area of restricted visibility, whether by day or night, the signals prescribed in this Rule shall be used as follows: (a) A power-driven vessel making way through the water shall sound at intervals of not more than 2 minutes one prolonged blast. (b) A power-driven vessel underway but stopped and making no way through the water shall sound at intervals of not more than 2 minutes two prolonged blasts in succession with an interval of about 2 seconds between them. (c) A vessel not under command, a vessel restricted in her ability to maneuver, a vessel constrained by her draft, a sailing vessel, a vessel engaged in fishing and a vessel engaged in towing or pushing another vessel shall, instead of the signals prescribed in paragraphs (a) or (b) of this Rule, sound at intervals of not more than 2 minutes three blasts in succession, namely one prolonged followed by two short blasts. (d) A vessel engaged in fishing, when at anchor, and a vessel restricted in her ability to maneuver when carrying out her work at anchor, shall instead of the signals prescribed in paragraph (g) of this Rule sound the signal prescribed in paragraph (c) of this Rule.

(e) A vessel towed or if more than one vessel is towed the last vessel of the tow, if manned, shall at intervals of not more than 2 minutes sound four blasts in succession, namely one prolonged followed by three short blasts. When practicable, this signal shall be made immediately after the signal made by the towing vessel. (f) When a pushing vessel and a vessel being pushed ahead are rigidly connected in a composite unit they shall be regarded as a power-driven vessel and shall give the signals prescribed in paragraphs (a) or (b) of this Rule.RULE 35—CONTINUED (g) A vessel at anchor shall at intervals of not more than one minute ring the bell rapidly for about 5 seconds. In a vessel of 100 meters or more in length the bell shall be sounded in the forepart of the vessel and immediately after the ringing of the bell the gong shall be sounded rapidly for about 5 seconds in the after part of the vessel. A vessel at anchor may in addition sound three blasts in succession, namely one short, one prolonged and one short blast, to give warning of her position and of the possibility of collision to an approaching vessel. (h) A vessel aground shall give the bell signal and if required the gong signal prescribed in paragraph (g) of this Rule and shall, in addition, give three separate and distinct strokes on the bell immediately before and after the rapid ringing of the bell. A vessel aground may in addition sound an appropriate whistle signal. (i) A vessel of 12 meters or more but less than 20 meters in length shall not be obliged to give the bell signals prescribed in paragraphs (g) and (h) of this Rule. However, if she does not, she shall make some other efficient sound signal at intervals of not more than 2 minutes. (j) A vessel of less than 12 meters in length shall not be obliged to give the above-mentioned signals but, if she does not, shall make some other efficient sound signal at intervals of not more than 2 minutes. (k) A pilot vessel when engaged on pilotage duty may in addition to the signals prescribed in paragraphs (a), (b) or (g) of this Rule sound an identity signal consisting of four short blasts.

RULE 36 Signals to Attract Attention If necessary to attract the attention of another vessel, any vessel may make light or sound signals that cannot be mistaken for any signal authorized

elsewhere in these Rules, or may direct the beam of her searchlight in the direction of the danger, in such a way as not to embarrass any vessel. Any light to attract the attention of another vessel shall be such that it cannot be mistaken for any aid to navigation. For the purpose of this Rule the use of high intensity intermittent or revolving lights, such as strobe lights, shall be avoided.

22) Great circle?

A great circle of a sphere is a circle that runs along the surface of that sphere so as to cut it into two equal halves. The great circle therefore has both the same circumference and the same center as the sphere. It is the largest circle that can be drawn on a given sphere.

Great circles serve as the analogue of "straight lines" in spherical geometry. See also spherical trigonometry and geodesic.

The great circle, also known as the Riemannian circle, is the path with the smallest curvature, and hence, an arc (or an orthodrome) of a great circle is the shortest path between two points on the surface. The distance between any two points on a sphere is therefore known as the great-circle distance. The great-circle route is the shortest path between two points across the surface of a sphere