Re: [Paddlewise] What's it called ...

Jack wrote;

(SNIP)

>     Took the Scrambler out on the post-frontal passage St. Mary's River
>     this evening --- 12 knots solid down the river with gusts five to
>     eight knots over that, low chop --- about a foot.  Interesting
>     phenomenon --- running downwind, the boat seemed to be showing a
>     weather helm, with a solid indication that it wanted to come all the
>     way around and back into the wind.  But it didn't --- just went into
a
>     "broach helm" (if there is such a thing), beam to the wind and
>     parallel to the seas.  Interesting!  Then I tried it into the
wind ---
>     and, left to its own devices, it neutralled out basically the same
>     way, abeam the wind and parallel to the troughs.  This does <not>
>     happen to the Pintail, and I'm a little confused by this tendency to
>     sit abeam the wind and parallel to the seas.  Is this a natural
>     tendency for most boats?  Any ideas to correct it?

Many boats tend to lay abeam in seas. The cause is the circular orbits of
water particles in the wave. The particles in the trough and crest travel
in opposite directions. So, if the boat is at any angle to the wave a
turning moment exists and persists until the boat reaches equilibrium.
Typically this is when the boat is parallel to the waves.

Not all boats do this and some will head downwind some upwind and some at
an angle. It depends upon the windage and underwater drag at various
angles. My recollection from reading about life raft safety is that any
long, narrow object floating in the water and in the absence of wind or
other outside force will align parallel to the wave and, if the windage is
balanced will align that way even in wind. For this reason life rafts are
usually round or some other shape with an aspect ratio of 1.0.

Skegs and rudders seem to cure excessive weather helm best. 

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/
.




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