"Gordon" wrote

http://www.youtube.com/watch?v=JxvP3DWi7_k

This is a good one

This is a one of the best examples of shallow water roll over dynamics that
I've seen and is similar to what Ken Barnes was describing in the clips I
saw. There are some differences however.

This incident happened in shallow water where the waves are feeling the
bottom so that the lower part is being slowed down while the breaking crest
continues at higher speed. If you look closely, you can see the impulse and
snap as the keel, entrained in the slower moving water, trips the boat as
tons of impact push on the topsides. If the boat had been end on, lower
resistance of the keel, greater longitudinal stability, and less topside
area to be acted on might have let the boat remain upright and only be
swept. There still would have been tremendous force on the companionway.
It looks as though it was open and the boat probably would have taken on a
lot more water if pooped. She probably would have kept her rig though which
would have been important if far from rescue. Easier to bail than re-rig.

It doesn't appear as if the wave was the 20 feet quoted. Looking at the
size of the crest and the boat makes it hard to believe how any boat could
survive tthe open ocean. However, waves break differently in deep water.
Without the bottom effect, there is less difference in velocity between top
and bottom. Waves combine until too high and steep to retain their shape.
Aided by the wind, the tops collapse. There still can be huge forces but
they are more vertical. This means that the wave crest has to be larger,
large enough for the weight of water above the boat to develope sufficient
force or for the boat to fall off the face. The probability of capsize is
orders of magnitude less or no one would be sailing deepwater in small
boats.

What this vidio illustrates beautifully is the extreme danger posed by waves
that are feeling the bottom. Anytime there is a big sea running and you are
in water less than twice the depth of the average wave height, this could
easily happen to you. Attempting to seek shelter through channels bounded
by shallow water while tired and scared is a perfect set up for this kind of
accident.

Whether in shallow water or deep, the vessel faces the same dilemma.
Staying end on to the seas reduces capsize risk. Speed may allow the boat
to surf ahead of the crest or maneuver to avoid the worst part. Both
however, increase the risk of plunging the bow into the back of the wave
ahead where the surface water is moving in the reverse direction. The
forward moving water of the following wave surface can be fast enough to
momentarily slow flow over the rudder enough to eliminate steering
effectiveness. Broaching into the trough of a wave in front of a collapsing
crest is av good set up for a roll over. A smaller boat may do better in a
some waves because it is too slow and short for the bow to reach the trough
before the wave passes. However, the smaller boat will experience the same
dangerous dynamics in smaller waves that it is more likely to encounter.

Statistics and probability factor into all of this in a major way. For
every set of wave conditions and even for each individual wave, there is an
optimum speed and course. Survival is maximized by having fresh, alert, and
skilled helmsmen that can constantly adjust. Fatigue eventually forces the
single hander or small crew to simply let the boat sail itself or, in
extreme conditions, lie a hull. It's then like sleeping in the middle of a
shipping lane. You may get run over and you may not.

From what I can descern of Ken Barnes' experience, it may not have been
sufficient to have maximized his chances of having just the right sail plan,
speed, and attitude for the conditions. This doesn't mean that the accident
happend because he wasn't up to the task. He could have been the most
experienced roaring 40's sailor on the planet at optimum speed and still
been hit by a wave running just enough differently from the rest to catch
the boat wrong. Someone could also do just about everything wrong and still
luck out. Ultimately, this is high stakes gambling. You can do a lot to
improve your odds but there are no guarantees on the outcome.

Nothing reveals the ignorance and lack of sea sense of armchair coastal
putterers more than the posts that Barnes must have been a poor sailor
simply because he lost his boat in the great southern ocean. There are few
simple and sweeping statements you can make about the sea. About the
closest is this, if you get your sailboat into conditions where large waves
are breaking due to bottom effect you are in deep, deep ****, man.