boating skills and seamanship

1Copyright 2007 - Coast Guard Auxiliary Association, Inc.

Boating Skills And Seamanship

Weather And BoatingChapter

12



Lesson Objectives

• Weather information sources• Basic storm patterns• Storm forecasting and precautions• Go, no go decision making• A personal weather equipment and

equipment check list



Weather Information

• What are some of the sources you can check for weather information?



Wind and Boating

• What can happen to a vessel caught in a storm?



Winds and Boating

• Storm surge• Swells• Breaking waves• Wave height• Wave frequency• Waves in shallow water• Fetch



Winds and Boating

• Storm surge is caused by raising sea levels in the low pressure areas around the storms. If these elevated sea levels reach shore they will add to high tide levels.

• Swells are waves coming from a distant disturbing force resulting in decreased heights and longer wave lengths.

• Breaking waves can occur on navigable waters as well as on shore. Shallow Water slows bottom of wave, top then spills over & breaks. Released energy can be dangerous.



Winds and Boating

• Wave height is dependent on wind strength, duration, and fetch. Wave height is classified (e.g. 3’ to 5’) by the range of wave heights which will occur 70% of the time.

• Wave frequency indicates gradient of wave face

• Fetch is the distance over which the wind blows uninterrupted on the water surface.



Winds and Boating

Table 12-1 Beaufort Wind Scale

Beaufort Number

Wind Description

Mean Wind Speed Equivalent (knots)

Mean Wave Height

Sea Conditions

meters feet

14 46Seas tumultuous. The air is filled with foam. The ocean is totally white with

driving spray. Visibility seriously reduced.64 +Hurricane12

7 23High waves; crests begin to tumbler; dense streaks of form. Spray affects

visibility.41-47Strong gale9

2 6.6moderate waves with a more pronounced long form; many whitecaps. A little spray.17-21Fresh breeze5

0-0.1 0-0.3Ripples without foam crests.1-3Light air1

- -Sea is like a mirrow.≤ 1Calm0

Copyright Hal Roth, 2006, reprinted with permission



Understanding Weather

• Weather and heat• Land heats faster than

water

• Land and sea breezes

Reprinted with permission fromGary Jobson’s Championship Sailing by Gary Jobson




• The CoriolisForce




• The air is warmed at the equator, rises, goes north and south, is cooled and falls again. When it reaches the earth, it goes north and south again, warms up, rises and repeats the cycle twice more resulting in three “doughnut” shaped air masses circulating on each side of the equator.

• The Coriolis Force, which turns moving masses to the right in the Northern Hemisphere and left in the southern, results in continuous wind patterns around the globe.




• Temperature and Humidity

• Moisture and energy• Air masses

• High pressure system contain cool, dense, dry air.

• Low pressure system contain warm, thin/rare, moist air which is energy laden




• Lows • Highs

Adapted from Boater’s Bowditch by Rickard K. Hubbard




• Why do we have inclement weather with a low pressure system?• A low pressure air mass is unstable, i.e., it is less

dense, or lighter than the surrounding air mass and therefore easily displaced.

• Low pressure air rises & cools, releasing moisture and energy




• Buys Ballot’s Law




• Fronts• Warm front• Cold front moving• Stationary front

warm front

cold front

stationary front



Cold Fronts




• Cold Fronts• Air Cooler Behind Than Ahead• Fast Moving• Can Create Violent Weather• When Passes

• Pressure Rises Abruptly• Temperature Falls• Relative Humidity Decreases• Wind Shifts Direction



Warm Front




• Warm Front• Air Warmer Behind Than Ahead• Slow Moving• Non-Violent Weather• Nighttime Fog Frequent• Can Have Long Periods Of Rain• When Passes

– Little Pressure Change– Little Temperature Change




• Clouds and Fronts• Who recalls the three types of clouds and

characteristics of each that accompany fronts?



Cloud Identification

• Cirrus • thin high-level made of ice crystals

• Stratus• Layered, flat

• Cumulus• Fluffy, White, Fair Weather Clouds• May Grow To Cumulonimbus (nimbo/nimbus =

rain clouds)



Cloud Families

• High - Cirriform• Cirrus, Cirrocumulus, Cirrostratus

• Mostly Ice – No Precipitation• Middle - Alto

• Altostratus, Altocumulus, Nimbostratus• Mostly Water

• Low• Stratus, Stratocumulus, Cumulus

• Mostly Water



High Clouds

• Cirrus• Mares’ Tails

• Cirrocumulus• Mackerel Scales

• Cirrostratus• Like A Sheet Or Veil



Cirrus (Ci)



Cirrocumulus (Cc)



Middle Clouds

• Altostratus• Mid-level, Layered

• Altocumulus• Cumulus Clouds Gathered In Layers

• Cumulonimbus• Rain Clouds• May Develop Into Thunderheads (Towering

Cumulus)



Cumulus



Towering Cumulus (Tcu)



Cumulonimbus (Cb)



Altocumulus (Ac)



Low Clouds

• Stratus• Low Layers Of Solid Cloud Cover

• Nimbostratus• Rain Clouds• Intermittent Or Steady Rain



Stratocumulus (Sc)



Stratus (St)




• Weather clues from clouds• Cold front clouds




• A cold front is comprised of dense air and as it moves it pushes all the air in front of it aloft where it cools forming cumulous nimbus clouds and heavy rains




• Weather clues from clouds• Warm front clouds




• High thin cirrus clouds ahead of a warm front.

• A warm front climbs over the colder air in front resulting in stratus clouds and a drizzling rain for an extended period of time.



Understanding Weather Pg 330

• Approaching low• Approaching warm front• Passing warm front• Within warm sector• Approaching cold front• Passing cold front




• Fog• Conditions favoring fog formation• Radiation fog

• Clear sky, little or no wind, temp & dew point about equal, burns off quickly

• Advection fog• Caused by warm, moist air blowing over cold

body; light wind < 15mph; slow to burn off• Predicting fog



Fog Precautions

• What precautions must be taken in fog?



Non-Frontal Weather

• Thunderstorms• Stage one• Stage two• Stage three

Reprinted with permission fromBoater’s Bowditch by Richard K. Hubbard



• Lightening

Thunderstorms

• Microbursts• Tornadoes• Waterspouts



Non-Frontal Weather

• What should you do if you are caught in a thunderstorm?



Thunderstorm

• Get to shore & let it pass• At sea

• Put on life jacket• Close ports and hatches• Note location of vessel• Reduce speed• Keep sharp lookout• Head into wind• Approach waves at 45 degree angle• Stay low in boat• Keep away from metal objects



Non-Frontal Weather

• Tropical Weather• Tropical Depression

• Wind Up To 34 Knots• Tropical Storm

• Wind 35 - 64 Knots• Hurricane

• Wind 65 Knots Or More• Also called

– Typhoon– Cyclone– Willy-Willy



The Go, No-Go Decision

• What are some of the considerations for making a decision to go or no-go?



The Go, No-Go Decision

• Is weather suitable for cruise?• Necessary equipment for safe operation• Crew confidence• Proper food and necessities• Getting weather info.• Boating and safety knowledge• Navigation ability• Back up plan• Float plan• Comfort level

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