CONTROLLABLE PITCH

PROPELLERS

BY K.V.V.UNNI

CONTROLLABLE PITCH PROPELLERS

BY K.V.V.UNNI

The SCHOTTEL Controllable Pitch Propeller –the reliable propulsion system for all ships with up to 30,000 kW

SCHOTTEL Controllable Pitch Propeller Systems (SCP) are available in various designs, including:• X-type, i.e. hydraulic cylinder mounted in the propeller hub• Z-type, i.e. hydraulic cylinder mounted in the propeller shaftOil is distributed either via an Oil Distribution (OD) box mounted in front of the gearbox (G-type), or via the W-type OD box, which ismounted in the shafting.

THEREFORE DIFFERENT COMBINATIONS OF HYDRAULIC CYLINDER ARRANGEMENT AND POSITION OF OIL SUPPLY CAN BE IMPLEMENTED. THE MOST COMMON IS THE X-TYPE HUB COMBINED WITH OIL SUPPLY IN FRONT OF THE GEARBOX,THE SO-CALLED “XG” CONFIGURATION.

OTHER SOLUTIONS ARE THE “ZG”VERSION, WITH THE HYDRAULIC CYLINDER IN THE SHAFT AND THE OD BOX IN FRONT OF THE GEARBOX, AND THE “XW” VERSION, WITH THE CYLINDER IN THE HUB AND THE OIL SUPPLY IN THE SHAFT.

THE “X” TYPE INCORPORATES A HYDRAULIC CYLINDER WITH THE PISTON DIRECTLY CONNECTED TO THE YOKE. HENCE THE DESIGN IS SIMPLE, WITH A MINIMUM OF MOVING PARTS, AND ACHIEVES THE HIGHEST RELIABILITY. TO OBTAIN OPTIMUM STRENGTH THE HUB IS CAST IN ONE PIECE. THE PROPELLER BLADES ARE MOUNTED ON LARGE-SIZED BLADE CARRIERS TO MINIMIZE THE STRESSES IN THE SYSTEM. THE YOKE MOVING INSIDE THE HUB IS SUPPORTED BY SLIDING PIECES. CRANK PINS ON THE YOKE OPERATE THE PROPELLER BLADE CARRIERS, WHICH HAVE GROOVES GUIDING THE PINS. THE PROPELLER BLADES ARE BOLTED TO THE CARRIERS. THE HUB IS SEALED BY A WELL-PROVEN SYSTEM CONSISTING OF A PRE-LOADED SEALING RING BETWEEN THE HUB AND THE BLADE FOOT.

The hydraulic oil flows through an inner and outer oil pipe, both mounted concentrically inside the hollow-bored shaft. The movable double oil pipe also functions as a feedback system indicating the current pitch of the propeller system. The Z-type hub with the hydraulic cylinder within the propeller shaft results in a considerably shorter propeller hub. The shaft-integrated hydraulic cylinder moves the yoke by means of a rod leading through the hollow-bored shaftline. For all systems, propeller blades and hubs are available made of Cu-Ni-Al or even stainless steel

The hydraulic oil flows through an inner and outer oil pipe, both mounted concentrically inside the hollow-bored shaft. The movable double oil pipe also functions as a feedback system indicating the current pitch of the propeller system. The Z-type hub with the hydraulic cylinder within the propeller shaft results in a considerably shorter propeller hub. The shaft-integrated hydraulic cylinder moves the yoke by means of a rod leading through the hollow-bored shaftline. For all systems, propeller blades and hubs are available made of Cu-Ni-Al or even stainless steel

CONTROLLABLE PITCH PROPELLERS DESIGNED BY SCHOTTEL OFFER THE FOLLOWING ADVANTAGES:• BLOCKING VALVES FOR PITCH SETTING INSTALLED IN THE CYLINDER SPACE OF THE HUB, EASILY ACCESSIBLE WHEN DOCKED WITHOUT DISMANTLING OF THE HUB • BLOCKING VALVES ALLOW OPERATION IN THE AHEAD CONDITION WITH 100% ENGINE POWER WITHOUT RESTRICTION • BLADES CAN BE DISMOUNTED IN A NOZZLE WITHOUT PULLING THE SHAFT • THE BLADE MOVING PIN IS PART OF THE CAST YOKE, WHICH ACHIEVES A LARGER CONTROL STROKE NEAR THE END POSITIONS OF THE BLADES, ALLOWING FINER PITCH CONTROL. THIS ALSO RESULTS IN LOWER STRESSES IN THE PIN. • OPTIMUM MATCHING OF MATERIAL BETWEEN HUB AND BLADE CARRIERS • LARGER HUB IS CAST IN ONE PIECE, GIVING A RIGID STRUCTURE

CONTROLLABLE PITCH PROPELLERS DESIGNED BY SCHOTTEL OFFER THE FOLLOWING ADVANTAGES:• BLOCKING VALVES FOR PITCH SETTING INSTALLED IN THE CYLINDER SPACE OF THE HUB, EASILY ACCESSIBLE WHEN DOCKED WITHOUT DISMANTLING OF THE HUB • BLOCKING VALVES ALLOW OPERATION IN THE AHEAD CONDITION WITH 100% ENGINE POWER WITHOUT RESTRICTION • BLADES CAN BE DISMOUNTED IN A NOZZLE WITHOUT PULLING THE SHAFT • THE BLADE MOVING PIN IS PART OF THE CAST YOKE, WHICH ACHIEVES A LARGER CONTROL STROKE NEAR THE END POSITIONS OF THE BLADES, ALLOWING FINER PITCH CONTROL. THIS ALSO RESULTS IN LOWER STRESSES IN THE PIN. • OPTIMUM MATCHING OF MATERIAL BETWEEN HUB AND BLADE CARRIERS • LARGER HUB IS CAST IN ONE PIECE, GIVING A RIGID STRUCTURE

DESIGNING A CP PROPELLER BLADE IS A COMPLEX PROCESS,REQUIRING AN EXTENSIVE RANGE OF EXPERT KNOWLEDGE IN THE SPECIALIZED FIELDS OF FLUID PHYSICS AND MECHANICAL ENGINEERING. IN ADDITION TO HYDRODYNAMIC BLADE DESIGN, THE CALCULATION OF HYDRODYNAMIC LOADS AND THEIR EFFECTS WHEN THE BLADE PITCH IS CHANGED AND IN VARIOUS OPERATING CONDITIONS ARE OF GREAT IMPORTANCE. IN ORDER TO PROVIDE ADVANCED BLADE SHAPES AND SATISFY EVER-HEIGHTENED REQUIREMENTS, USE IS MADE OF STATE-OF-THEART CALCULATION METHODS, REFINED CONTINUOUSLY BY MEANS OF RESEARCH PROJECTS CARRIED OUT IN COOPERATION WITH RESEARCH INSTITUTES.THE BLADE DESIGN IS INITIALLY EXECUTED THROUGH THE USE OF CIRCULATION THEORY VERIFICATION AND OPTIMIZATION TECHNIQUES

THE STRENGTH OF THE BLADE IS VERIFIED THROUGH THE USE OF FEM (FINITE ELEMENT METHOD), ACHIEVING THE OPTIMUM COMBINATION OF MECHANICAL EXPEDIENCE AND HYDRODYNAMIC EFFICIENCY.ALMOST EVERY PROPELLER UNDERGOES EXTENSIVE MODEL TESTS, WHERE IT MUST PROVE THAT IT ACTUALLY POSSESSES THE REQUIRED CHARACTERISTICS WITH REGARD TO EFFICIENCY, CAVITATION AND PRESSURE FLUCTUATIONS.

Here SCHOTTEL employs two tried-and-tested methods developed at the HSVA in Hamburg and the SVA in Potsdam, which are currently the most powerful programs in existence. Openwater diagrams, pressure distribution, cavitation and pressure fluctuation properties are calculated for all relevant operating states in the vessel’s wake.

In addition to close cooperation with research institutes, SCHOTTEL also draws on the invaluable years of experience of leading experts in the field of propeller design.

Here SCHOTTEL employs two tried-and-tested methods developed at the HSVA in Hamburg and the SVA in Potsdam, which are currently the most powerful programs in existence. Openwater diagrams, pressure distribution, cavitation and pressure fluctuation properties are calculated for all relevant operating states in the vessel’s wake.

In addition to close cooperation with research institutes, SCHOTTEL also draws on the invaluable years of experience of leading experts in the field of propeller design.

The strength of the blade is verified through the use of FEM (Finite Element Method), achieving the optimum combination of mechanical expedience and hydrodynamic efficiency. Almost every propeller undergoes extensive model tests, where it must prove that it actually possesses the required characteristics with regard to efficiency, cavitation and pressure fluctuations.In these tests the SCHOTTEL design regularly competes head-to-head with technology from other suppliers, and as the results show, SCHOTTEL produces some of the best propeller designs on the market.

The pump and motor unit forms an essential part of the hydraulic system. This assembly delivers the oil quantity needed for adjustment of the propeller blades and produces the pressure required for pitch control. Two electrically driven pumps (1 active pump, 1 standby pump, each with 100% capacity) are mounted on the cover of the hydraulic tank, with the pumps running in the oil

The pump and motor unit forms an essential part of the hydraulic system. This assembly delivers the oil quantity needed for adjustment of the propeller blades and produces the pressure required for pitch control. Two electrically driven pumps (1 active pump, 1 standby pump, each with 100% capacity) are mounted on the cover of the hydraulic tank, with the pumps running in the oil

The compact control block, incorporating all the indicators and the individual instruments necessary for pitch control, is located on the top of the tank. The piping between the pump and motor unit and the oil supply unit is part of the shipyard’s scope of supply.

Lubrication oil is fed through the stern tube into the hub.

This system is not connected to the hydraulic system of the controllable-pitch propeller unit. Optionally a two-pipe system can be supplied, in which case the hydraulic oil is used to lubricate

The remote control system is designed to provide automatic control of a SCHOTTEL controllable pitch ropeller. The system is based on a microprocessor-controlled system architecture with 2-wire bus communication between central unit, ECR and bridge. An HMI (human-machine interface) allows clear, user-friendly control, set-up and maintenance of the system.The system is type-tested to GL,LRS and ABS (other classes on request) and meets class requirements according to AUT24 and UMS.Standard features

UMS.STANDARD FEATURES:• CONTROL FROM ECR, BRIDGE AND WINGS• COMBINATOR AND CONSTANTSPEED MODE• UP TO 3 ACCELERATION PROGRAMS• LOAD CONTROL MANAGEMENT• AUTOMATIC SLOW DOWN• AUTOMATIC SHUT DOWN• SELF MONITORING• NON-FOLLOW-UP CONTROL FROM ECR AND BRIDGE• PITCH MEASUREMENT SYSTEM• M/E INTERFACE :THE SYSTEM IS POWERED WITH 24 V DC. A SEPARATE SUPPLY SHOULD BE PROVIDED FOR THE BACK-UP SYSTEM.OPTIONS:• ENGINE TELEGRAPH SYSTEMS AND ELECTRIC SHAFT SYSTEM IN THE WHEELHOUSE AREA• CLUTCH CONTROL SYSTEM• INTERFACE FOR DP SYSTEMS• INTERFACE FOR MANOEUVRING

UMS.STANDARD FEATURES:• CONTROL FROM ECR, BRIDGE AND WINGS• COMBINATOR AND CONSTANTSPEED MODE• UP TO 3 ACCELERATION PROGRAMS• LOAD CONTROL MANAGEMENT• AUTOMATIC SLOW DOWN• AUTOMATIC SHUT DOWN• SELF MONITORING• NON-FOLLOW-UP CONTROL FROM ECR AND BRIDGE• PITCH MEASUREMENT SYSTEM• M/E INTERFACE :THE SYSTEM IS POWERED WITH 24 V DC. A SEPARATE SUPPLY SHOULD BE PROVIDED FOR THE BACK-UP SYSTEM.OPTIONS:• ENGINE TELEGRAPH SYSTEMS AND ELECTRIC SHAFT SYSTEM IN THE WHEELHOUSE AREA• CLUTCH CONTROL SYSTEM• INTERFACE FOR DP SYSTEMS• INTERFACE FOR MANOEUVRING

6 Passenger/Container vessel ZI YU LAN,1 x SCP 1544 XG (15,000 kW)Shipyard: Aker-MTW, Germany, Owner: Shanghai Shipping Corporation,PR China

Diameter: it is the diameter of the circle swept across the extreme tips of the propeller blades. Shaft speed (usually engine rpm divided by the reduction gear ratio) and SHP are the factors influencing the diameter. SHP (Shaft Horse Power) is the power actually delivered from the engine to the shaft thus to the propeller, about equal to the BHP (Brake Horse Power, meaning the maximum engine horse power as tested at the factory) minus about 3% of power loss at the gearbox and 1.5% per bearing. Generally the larger the diameter the greater the propeller efficiency

Pitch: it is the distance a propeller drives forward for each complete revolution, assuming it is moving trough a solid element, just like a wood screw does. For instance, if the propeller cover 100 millimeters per turn through a solid, then its pitch is 100 millimeters. There are three main propellers' families: constant-pitch propellersfolding propellers and controllable-pitch propellers

Pitch: it is the distance a propeller drives forward for each complete revolution, assuming it is moving trough a solid element, just like a wood screw does. For instance, if the propeller cover 100 millimeters per turn through a solid, then its pitch is 100 millimeters. There are three main propellers' families: constant-pitch propellersfolding propellers and controllable-pitch propellers

Constant pitch propellers: this type of propellers blades are welded to the hub, and their pitch, as suggested by the name, is fixed.

Their structure is surely the stronger, because they are manufactured from a single casting, usually through CAM (Computer Aided Manufacture) assisted machinery and they have no moving parts.  

Folding propellers: they have folding blades; under sail the hydrodynamic pressure keeps them closed, thus considerably reducing drag. Their astern maneuverability is poor.

Controllable pitch propellers: in this type of propellers, the user can modify the pitch, while underway, by mean of a hydraulic mechanism or a direct mechanical linkage. Feathering propellers, in particular, are a special controllable pitch propeller type, ensuring low drag, because of their characteristic blade design. Controllable pitch propellers are very practical because by modifying the pitch they allow for thrust optimization under different load conditions. Most modern sailboats are fitted with this type of propeller. Lets discover together how to use it.

FOR THE MAJORITY OF ENGINE AND PROPELLER MANUFACTURERS THE IDEAL PROPELLER WILL CAUSE A LOSS OF 5 TO 10% IN ENGINE MAXIMUM REVOLUTION PER MINUTE; IF, FOR INSTANCE, THE ENGINE RATED MAXIMUM RPM ARE 3600, THE LOSS WILL APPROXIMATELY BE 200 RPM, IN CALM SEA, WITH NO WIND, WITH NO OVERLOAD ON BOARD AND WITH A CLEAN HULL BOTTOM, WHILE IT WILL BE ABOUT 360 RPM IN ROUGH SEA, STRONG WIND ETC...

IF THE TOTAL ACTUAL LOSS IS BIGGER, THEN THE PROPELLER IS "OVERLOADED" AND SO IS THE ENGINE, WHILE IF THE PROPELLER IS TURNING TOO FAST IT IS "UNDER-LOADED" AND IS NOT USING ALL THE ENGINE POWER. ON THE OTHER HAND SOMEONE BELIEVES THAT ONE SHOULD KEEP THE PITCH AS LONG AS POSSIBLE IN ORDER TO ACHIEVE THE CRUSE SPEED AT LOWER AS POSSIBLE RPM.

For example, lets suppose that a 6 knots cruise speed is reached at 2800 rpm. Increasing the pitch (and of course keeping the diameter constant) the same speed could be registered at 2000 rpm. In this case, advantages are: lower engine speed, less shaft vibration, less noise thus longer engine life. The question is: which is the right choice?

THE "HIGH PITCH AND LOW RPM" SOLUTION , ALTHOUGH APPEARING INTERESTING, IS NOT THE CORRECT ONE. THE ENGINE IS ACTUALLY RUNNING SLOWLY, BUT IT IS OVERLOADED THUS LASTING SHORTER, MUCH SHORTER THAN AN ENGINE RUNNING FASTER BUT WITH LESS "JOB" TO DO

. This is due to the higher stress concentration on the engine pistons, crankshaft and bearings, which can lead to some serious damage such as engine seizing. Having an "overloaded" engine and propeller is just like someone driving on a steep mountain road on the fifth gear instead of the third: the engine is overheated, the speed does not increase and fuel consumption is higher. On the other hand the "5 to 10% loss on top rpm" rule will surely not overload the engine, while it will generate noise and the transmission gear will be in danger. The propeller will turn faster, thus increasing shaft and bearings vibrations The ideal solution is an average of the two and can be obtained with practical tests

The first thing to do is to find in the owner's manual at which rpm the engine reaches its maximum power (BHP). Lets perfectly working injection system. This means, for instance, that an engine which has lost say, for example, that the maximum power is obtained at 3600 rpm. Then we have to check which is the actual rpm reached by the engine, accelerating in neutral. If a 3700/3750 rpm are achieved, everything is fine, if not you have to adjust your revolution counter to that value (in fact, and normally, an engine should increase, in neutral, 3 to 4% its maximum rated rpm, because, usually, the manufacturer takes into account the loss due to the reduction gear). All this is applicable to all well maintained engines, and in particular to those with clean fuel filters and compression will not achieve its top rated rpm. Once the revolution counter has been verified, we can start the trial which will allow us to know if and at what rpm our engine is overloaded.

THE SEA STATE MUST BE CALM, AND NO SAIL SHOULD BE UP. KEEPING A CONSTANT ROUTE, WE HAVE TO INCREASE ENGINE SPEED WITH A 200 RPM STEP. WE WILL PLOT, FOR EACH RPM RANGE, THE BOAT'S SPEED, OBSERVED AT THE LOG (GPS COULD BE TOO INACCURATE FOR THIS PURPOSE). SPEED SHOULD INCREASE CONSTANTLY FOR EACH RPM RANGE. MEANTIME, WE SHOULD CHECK EXHAUST WATER AND FUMES COLOR, WHICH MUST NOT CHANGE. IF SPEED DOES NOT INCREASE CONSTANTLY OR DOES NOT INCREASE AT ALL, THEN THE ENGINE IS OVERLOADED (BE SURE THAT YOU HAVE NOT REACHED THE HULL SPEED); EXHAUST FUMES QUANTITY AND WATER COLOR WILL PROOF THE OVERLOADED ENGINE CONDITION

IN FACT, INCREASING ENGINE LOAD,QUANTITY, DENSITY AND COLOR OF BOTH EXHAUST FUMES AND WATER WILL BECOME DARKER AND DARKER, TILL THEY RICH A BLACK COLOR, MEANING PITCH IS TOO LONG. IN THIS SITUATION, INCREASING RPM WILL NOT INCREASE SPEED, SOME OF THE FUEL WILL NOT BE BURNED AND FUEL CONSUMPTION WILL INCREASE WITHOUT BENEFITS THE SAME TEST SHOULD BE CARRIED OUT WITH ROUGH SEA AND WIND AND THE RESULTS PLOTTED; THESE WILL INDICATE IF YOUR PROPELLER'S PITCH IS CORRECT OR IF IT SHOULD BE INCREASED OR DECREASED

THEN LETS CHECK AGAIN THE ENGINÈS OWNER MANUAL, WHERE WE WILL FIND THE MAXIMUM HORSEPOWER OUTPUT AND THE HP/RPM RATIO. LETS, NOW, FIND THE BEST HP/RPM RATIO. WE WILL ASSUME OUR ENGINE WILL DELIVER THE MAXIMUM HORSEPOWER OUTPUT AT 3600 RPM, AND THAT A 2 HP POWER INCREASE IS ATTAINED FOR EVERY 500 RPM TILL 2800 RPM, THEN 1.5 HP TILL 3200 RPM AND THEN 1 HP TILL 3600 RPM. THE BEST HP/RPM RATIO IS AT 2800 RPM

We know that cruise engine speed is 20% less than its maximum speed (3600 rpm): the closest we go to this value the better is our propeller pitch. For instance, if our engine has its maximum efficiency at 2800 rpm and its maximum full ahead rpm are respectively 3500 in calm sea and 3300 in rough sea, than our pitch is correct (3500 rpm minus 20% equals to 2800 rpm). This is true if our test result confirm that the engine has not been overloaded in the 0 to 2800 rpm range, otherwise the pitch has to be reduced

Design System Propellers are designed with the most suitable method satisfy the needs of each ship operation.The methods include applying conventional planning methods based on systematic model-testing of the series of propellers, utilizing various databases, and analyzing the propeller's efficiency and characteristics computed by propeller theoretical calculation. In particular, the Propeller Characteristic Analysis Method, employing Non-linear Lifting Surface Theory supported by the Vortex Lattice Method (VLM), estimates propeller characteristics with pure logic based on the difference of blade profile and blade section, and the variation of working condition Thus, we immediately can obtain the effect of propeller characteristic, and its performance according to different environments.All the information thus gained is applied to our designing work to pursue efficiency

Analytical System Using various analytical software programs including the Finite Element Method, Kamome Propellers undergo strength analysis if need be, to establish the efficiency, characteristics, and strength at the most suitable states.We also use three-dimensional CAD to examine the best form of section and in establishing numerical data of the section and utilize the collected information for development of product with precise quality.

Manufacturing System KAMOME'S CAM (BLADE PROCESSING SYSTEM) IS INTEGRATED WITH A CAD SYSTEM. TWO INSTALLATIONS OF SIMULTANEOUS FIVE-AXES NC BLADE MILLING MACHINE THAT PROCESS CPP AND FPP RESPECTIVELY TO THE MOST SUITABLE STATE CAN PROVIDE ACCURATE PROCESSING. NOT LIMITING THE PROCESSING, THE PROPELLER'S OPTIMUM FORM DECISION CAN BE VERY FLEXIBLE.ALL MANUUFACTURING DATA IS STORED IN OUR DATABASE, AND BECOME AVAILABLE AT THE TIME OF REPRODUCTION

SYSTEM OPERATION

GO TO THE MASTER CONTROL CABINATE LOCATED AT CO2 ROOM OR FIRE CONTROL STATION 1.        KEY BOX1) BREAK GLASS2) TAKE THE KEY2.        OPEN THIS DOOR 3.        ENSURE ALL PERSONNEL HAVE EVACUATED THE PROTECTED SPACE 4.        CLOSE DOORS AND HATCHES 5.        OPEN ONE CYLINDER VALVE 6.        OPEN VALVE No1 & No2 7.        SYSTEM WILL RELEASE CO2 AFTER A TIME DELAY OF 30 SECS IF NOT FOLLOW EMERGENCY OPERATION ON INSTRUCTION

CHART NOW SYSTEM IS OPERATED

E IN CASE OF FAILURE IN THE OPERATION OF THE SYSTEMPNEUMATICALLY FROM THE CO2 ROOM GO TO THE CO2 ROOM1.        REMOVE SAFETY PIN FROM PRESSURE/MANUAL ACTUATOR ON RELEVANT CYLINDER VALVES 2.        OPEN RELEVANT MAIN VALVE BY HAND PULL DOWN THE LEVER ON PRESSURE/MANUAL ACTUATORS BY HAND

AFTER DISCHARGE1.        ALLOW ENOUGH TIME FOR THE CO2 GAS TO EXTINGUISH THE FIRE 2.        DO NOT REOPEN THE SPACE UNTILL ALL REASONABLE PRECAUTIONS HAVE BEEN TAKEN TO ASCERTAIN THE FIRE IS OUT 3.        WHEN THE FIRE IS OUT, VENTILATE THE SPACE THOROUGHLY PERSONS RE-ENTERING THE SPACE MUST WEAR COMPRESSED AIR BREATHING APPARATUS UNTIL THE ATMOSPHERE HAS BEEN CHECKED AND FOUND TO

CONTAIN 21% OXYGEN CONTENT

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