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From: Eric Thompson (no email)
Date: Mon Oct 01 2001 - 21:42:34 EDT
Gene,
REAL GOOD. Next time leave out the stuff about when you are
on a wave. Most people already 'get' surfing.
Eric Thompson
S/V Procrastinator
South San Francisco
gene said'
It took me a long time to understand the relationship, now
if I can only
write it so it makes sense!
First, waves are a set distance apart for any speed they are
traveling, or
maybe it would be better to say that as the speed of a wave
increases, it
gets farther apart. That formula that tells hull speed is
the one that
tells how far apart waves are at a certain speed. It's no
coincidence.
The faster a wave travels, the farther apart each is. The
bow of your boat
makes a wave. The wave's speed is the same as your boat
speed, just
because the front of your boat is pushing it at the speed it
is going. The
next wave behind it is going to be a distance behind the
first (and by
default, the same distance behind the front of your boat)
that corresponds
to the formula. As long as that second wave is under the
boat, the boat
is on flat water, supported front and rear.
Once the boat goes fast enough that the second wave is
behind the boat
(exceeds hull speed) the rear of the boat falls into the
trough. The
faster the boat goes, the deeper the trough becomes, the
farther to the
middle of the distance between the waves the rear of the
boat goes and the
farther the rear of the boat drops. Instead of sailing or
motoring on flat
water, it's now trying to sail or motor on the face of a
wave, a wave it
created it's self.
So you can see if the boat is longer, it will stretch across
a longer gap
between waves and still be on level water (at least as far
as the boat is
concerned) I'm sure it takes more power to push a bigger
boat through
water, but it nothing compared to the power needed to push
it up a steep
face of a wave.
Once a boat gets on a plane, it is riding on top of the
water and the
waterline length doesn't come into play, since the waves no
longer have
anything to do with it. But you'll notice that before it
gets on a plane,
it has to ride up a very steep wave.
I'm sure most of us have sailed where there are sizable
waves. Have you
noticed that as you go down the face of a wave your boat
speed increases,
possibly far beyond hull speed? That is simply because you
have the
reverse in play, the front is not supported level, it's in a
trough and
it's sliding down the wave. Hull speed there would only
come into play
once your speed is so great that the wave you're making
inside of the big
wave leaves your boat dropping below level in the back (or
the waves
catches up to you and you end up on the back side of it!)
Did I make any sense or just confuse things?
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