GTSC Keelboat Class Spring 2005
Davis King and Greg Matthews
Weather
Weather is the third most dangerous aspect of sailing. (The first is the crew, and the
second is alcohol). Weather brings not only obviously visible dangers such as lightning,
tornadoes, and squalls but also less visible ones such as hypothermia, heat exhaustion,
heat stroke, dehydration, and being stranded in a dead calm. The skipper of a boat needs
to understand weather well enough to assess the risks of all of these dangers before
setting sail, and to recognize dangerous weather situations as they develop. Furthermore,
when the weather isn't dangerous, understanding it will help you to plan trips and to sail
more effectively.
I.
Responsibility
a. Every keel skipper is responsible for getting a weather report before going
up to the lake, EVERY time. Period. There are plenty of clear days with
dangerous weather conditions developing over the horizon. And, on the
clearest days, you will want to know whether or not there will be wind.
b. Internet, TV, weather radio – forecasts are easy to get now, and in this
area, they will give you 90% of the warnings you need.
i. Note that in other areas, they may be less effective – on the GA or
FL coasts, thunderstorms can develop quickly in the afternoon of a
beautiful day with no forecast of rain. That is not an issue here.
ii. A bigger problem here is that they will over-warn you – they will
usually predict more wind than exists, and more rain and storms
than actually happen. You will need your eyes, and a basic
understanding of weather systems to know which warnings are
serious. You will also need enough judgment to know that your
guesses about the weather will sometimes be wrong.
iii. Usually Accurate: "WINDY", "caution on area lakes," "severe
storm warning," "flood watch/warning," major front expected,
"tornado watch/warning" (if not highly localized).
iv. Very inaccurate: wind forecasts other than WINDY. X% chance of
rain, other than a front or major storm
v. Weather is often completely different on Lake Lanier and in
downtown Atlanta.
c. We will cover
i. Recognizing changing weather while sailing
ii. Basics of interpreting forecasts for Lake Lanier
iii. Handling bad weather
II.
Recognizing Changing Weather – Beaufort Scale
a. The Beaufort Scale is a simple but highly effective tool to help you
estimate the wind speed while sailing. This helps you in racing, alerts you
to calms, and alerts you to the need to prepare for gusts or to reduce sail.
i. In particular, if a clear line of dark, rough water with steady
whitecaps is moving towards you, free sheets and drop sails!
b. 13 categories (forces), identified by
i. how the surface of the water looks
ii. how objects on land behave in the wind
iii. how boats react to the wind
1. was originally developed in the British Navy, based on
which sails a square-rigged ship could carry given the wind
iv. Force 0 – dead calm, water like glass
v. Force 5 – lots of whitecaps, some spray, wild ride on dinghy. The
maximum for many dinghies.
vi. Force 12 – hurricane
vii. The point is, this is BETTER than having a wind meter on your
boat, b/c you can see the wind via the Beaufort Scale BEFORE the
wind reaches you. You can therefore prepare.
c. The scale
i. We will NOT expect you to memorize the scale or to know the
MPH of Force 3 etc. or how to tell the difference between Force 6
and Force 7.
ii. We do expect you to be able to know the general order of
conditions.
1. glassy -> ripples -> waves -> whitecaps -> spray -> foam
2. trees are still -> leaves rustle -> leaves moving constantly > small branches move -> large branches move -> whole
trees shake -> twigs break off -> branches break off -> trees
uprooted
3. as the wind rises
a. lighter color water -> darker color water
i. until you reach white squall
b. waves grow larger, then larger & steeper
c. whitecaps are more frequent
d. waves develop ripples, then spray, then foam
iii. Note also that the MPH need to be adjusted for different bodies of
water. In general, smaller bodies of water have smaller waves, b/c
the waves don't have enough room and time to build up.
1. waves (or whitecaps) on a small lake indicate more wind
than the same height of waves on a big lake; more on a big
lake than on the Gulf of Mexico; more on the Gulf than on
the ocean
III.
IV.
Recognizing Changing Conditions – Sky and Clouds
a. Wind effect
i. Even small clouds have a noticeable effect on the wind. Typically,
the wind is greater near the edge of a cloud than either out in the
sun or under the cloud.
ii. There are three reasons for this:
1. Clouds sometimes represent a barrier between two weather
systems, with a buildup of wind or storm-producing energy
along the barrier.
2. temperature differentials can contribute to wind – if the air
temperature is constant over a large, sunny area, there is
little reason for it to move.
a. Sea breeze and land breeze
b. Cold front/warm front
3. Clouds are not constant – every cloud has a circulation of
air that either brings moisture and energy into the cloud
(growing) or takes moisture and energy out of the cloud
(shrinking). This circulation produces wind on the edges of
the cloud, but directly under the cloud it can be straight
up/straight down.
iii. Note that if clouds are growing, they can lead to afternoon,
summer thunderstorms.
Squalls and thunderstorms
a. Danger of a cloud is related to its height, its size, and its color.
i. Dark/black clouds are the #1 sign of trouble.
ii. White clouds are fine.
iii. Grey clouds often bring drizzly but harmless rain. But there are
frequently darker clouds or storms hiding among the grey clouds.
iv. Thunderstorm:
1. very tall clouds
2. 'anvil' shape at top/anvil head
3. dark/black
4. In hot, humid weather, can develop in a couple hours from
small, puffy clouds that grow.
5. Lightning can strike from as far away as 6-10 miles.
6. Extremely violent and unpredictable winds. You do not
want to kid around with thunderstorms or to attempt to sail
through one. Especially severe thunderstorms.
7. Summer thunderstorms as opposed to thunderstorms
brought by a front typically don't last very long.
v. Squalls
1. A front can bring either thunderstorms, squalls, or grey rain
clouds with high but not squall-like winds.
2. What makes it a squall is not the wind speed, but its
constant shifting and unpredictability. This makes squalls
very dangerous for sailboats, and can make it impossible to
sail through them.
a. Frequent auto-tack shifts, can be knocked down to
either side, people easily knocked overboard
3. Recognize a squall by:
a. Sudden temperature drop
b. Sudden large change in wind speed and/or direction,
especially if you can see the change moving
towards you as a line on the water, with darker or
rougher water on the other side of the line. Often
rain begins at or near the squall line.
c. Seeing other boats get knocked over
d. If the approaching line is white and foamy instead
of dark, well, get a knife ready for the halyards.
4. In a squall
a. Drop sails ASAP. Drop sails from front to back –
first spinnaker then jib then main.
b. Lifejackets on.
c. Close hatch, get as many people down below as
possible, for warmth, dryness, and stability.
d. If rain or significant spray, watch for water getting
in the boat
e. Once you are in the squall, use a motor or reefed
main (carefully) to get to shelter (dock, anchor, or
area where wind is blocked). Docking may be
difficult and dangerous.
f. Operate at lower speed than normal.
g. If waves are large, sail at an angle diagonal to the
waves.
i. Don't try to sail directly into or away from
the waves (heavy pounding + bow or stern
can get plowed under).
ii. Don't try to sail directly parallel to the
waves; that will maximize rolling, get a lot
of water into the boat, and can capsize or
swamp a small boat
iii. You are highly unlikely to see waves on
Lanier than can threaten the J or C&C, but
you will sometimes see waves that can make
the ride uncomfortable for the people and
bad for the equipment
1. raising/lowering sails very difficult
in waves
2. people do get seasick on Lanier!
vi. Tornadoes/Waterspouts
1. This is likely the worst you will see on Lake Lanier
V.
VI.
2. Often develop in severe thunderstorms or fronts with lines
of thunderstorms. This is why you need to listen to severe
thunderstorm warnings! Do not go out in boats when a
severe thunderstorm warning is in effect or when tornadoes
are possible.
3. There are certain sky conditions that can indicate possible
tornado formation. Often there are dark clouds, with a
funny color to the sky under the clouds. Sometimes, wisps
of twisted cloud below a solid, otherwise flat-bottomed
dark cloud.
4. The goal is not to be near a tornado. There is little you can
do while on a boat, except to do the procedure in a squall,
get your sails down, and get the crew down below.
Understanding Forecasts
a. Every area has its own weather patterns. For coastal areas with a lot of
racing, you can buy guides to the local sailing weather.
i. Typical wind direction, speeds
ii. Which directions storms come from
b. On Lanier:
i. the forecasts usually overstate the wind, unless there a front is
passing through or has passed through within the last 2-3 days.
Then, the wind may greatly exceed forecast.
ii. the water temperature is also surprisingly cold throughout the
winter and spring. Can get hypothermia very quickly. The water
takes a long time to heat up (weeks and months) after the air turns
warm.
iii. With a cold front, you can be sailing in august with full foul
weather gear, and still be shivering
iv. More often, your crew in summer will be hot, bored, frustrated
c. US Weather patterns
i. Move from west to east
ii. Storms here can come from Gulf of Mexico or from
Texas/Oklahoma
iii. Rarely, remnants of hurricanes can make it up here from Gulf
iv. When looking at weather map, therefore, check out the weather to
the west, with some attention to possible storms in the northern and
western Gulf.
Weather Maps
a. High and low pressure systems
i. High pressure == sunny, few clouds, low winds
ii. Air flows from high pressure to low pressure
iii. Winds are clockwise around high in northern hemisphere,
counterclockwise around low
iv. Low or falling pressure == bad weather, rain, higher winds and
squalls
v. The faster the pressure falls, the worse the weather
VII.
vi. Fronts generally are lows, with highs in between the fronts
b. Isobars are lines of constant pressure on weather map.
1. they show the pressure gradients
2. the wind typically flows somewhere between parallel to the
isobars and from the high to the low. Spiraling in towards a
low
3. lots of isobars close together == high winds
4. lower low pressure == high winds
ii. the air must go somewhere as it spirals in towards a low
1. where? – up, rising and making clouds and storms
c. Fronts
i. Where air masses with different temperature meet
ii. Energy created by the temperature and pressure differences
iii. Cold front: cold air pushes under the warm air, forces it up, creates
lots of thunderstorms and squalls. Squall line near cold front.
Sudden temperature drop signals a powerful cold front w/ many
storms. Sometimes the drop precedes the storms
1. Winds change direction as much as 180 degrees or more
when cold front passes
iv. Warm front – warm air pushes over, rises above cold air mass.
Rainy, but milder than cold front
1. winds don't change direction as much in warm front
v. when forecast is calling for rain, knowing whether it is warm or
cold front or scattered afternoon thunderstorms will tell you a lot
about the danger to sailors.
vi. Northeaster – a major cold front that stalls out, sitting over the
same area for several days. Usually, it stalls out over the coast, but
ATL can be on the back edge of one
d. Other
i. Microbursts, hurricanes
Handling bad weather
a. #1 concern – keep an eye on your crew
i. sick, hypothermic, or dangerously hot people often get quiet, go
below, or get out of the way. You have to look actively for
developing medical problems. If someone is in cabin, not coming
out for extended period, keep checking on him/her. Ask regularly
if crew are ok
ii. order lifejackets when you judge it necessary, and offer/encourage
lifejackets long before it is necessary
iii. foredeck person needs lifejacket first
b. #2 concern – reducing sail, changing behavior as wind rises
i. give more time for tacks, jibes, sail changes in high winds
ii. even shouted commands may not be heard
iii. equipment is much more likely to break
iv. boat is more difficult to control near other boats or dock
v. Reduce sail – smaller jibs, drop jib and spinnaker before main
VIII.
vi. Reefing the main
1. both J24 and C&C have sails with reefing points
2. Reefing lowers the center of effort and reduces sail area.
Lowering the CE has big effect on heel
3. Reefed main and blade have better helm balance, control
than full main alone
4. Ask to have this demonstrated on the boat
5. Can either do it at dock or underway
6. secure the new tack and the new clew tightly, loosely tie
the middle reefing points to keep sail even/out of the way
7. don't overtighten
Weather-related medical problems
a. Dehydration
i. Warning signs: anger, irritability, headache. Often crew arguing is
sign of dehydration
b. Hypothermia
i. Bluish, cold, can't stop shivering
ii. This is life threatening
iii. Get person off the water asap
iv. Use blanket, body heat to warm person up
c. Heat exhaustion
i. Take action right away to get person out of sun, on land, and to
cool him/her down
ii. Biggest danger is that it will turn into heat stroke if it continues
d. Heat stroke
i. This is a 911 life-threatening emergency.
ii. When you stop sweating, it is bad.
iii. When your skin stops feeling cool or clammy and starts feeling
hot, it is bad