Re: Diminishing Returns

Steven W. Barnes (oldsurfdude@worldnet.att.net)
Wed, 10 Mar 1999 18:02:39 -0800


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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Lars S. Mulford wrote:
>
> Secondly, when Barry Foy finally set up "Always" correctly in regard to mast
> position and secure mounts, she really performed startlingly well. I know
> that folks like Harry and others have tried to figure out why this is, but I
> never did figure it out. All I know is that except on extreme points of
> sail, "Always" would outperform standard rigged P15s. Now granted, the
> standard rigs point a bit higher (as Harry has noted too) but the difference
> is less than you'd think.

I think I know why from reading "Sails" by Derek Harvey, a great book,
by the way, with very readable clear explanations of the 10 most common
sailing rigs, and lots more, too.

As you point higher, turbulence will start in at luff edge of the sail
and creep farther back along the sail, as you point higher and higher,
until the turbulence spreads so far back along the foot length of the
sail that the sail completely "luffs." As you point lower, turbulence
will start in at the leach of the sail and gradually work it's way
forward, the more you fall off, until the sail stalls. The key is the
length of the foot. The longer the foot, the farther back the luffing
can creep, or the farther forward the stalling can creep, without being
completely stalled.

A P-14 with a 8' foot has a short amount of creeping distance compared
to a 13' lateen foot. So even though not drawing optimally, the lateen
sail can still be drawing adequately through a larger window of angle of
attack. An optimally trimmed sloop rig with jib and main will
theoretically be faster, but in practice is usually not, because it is
much harder to keep the jib, main, and jib and main together, optimally
trimmed.
That window of acceptable angle of attack for the jib/main is very
narrow and precise, and is usually not maintained for more than a few
minutes at a time due to constant changes of wind velocity, swells,
etc. And when you make one sail adjustment on a sloop rig, it usually
means everything else is now off, and needs adjusting, also. With every
adjustment it takes a few minutes to achieve a smooth flow of wind over
the sails again. Good racers don't adjust constantly, just frequently.

Is this all perfectly clear?

To put it briefly, the lateen sail stays in adequate trim more of the
time, more easily, with fewer adjustments, maintaining good air flow,
than does the sloop rig. So I guess the casual lateen skipper will beat
the casual sloop skipper, but watch out for those Judy's, Jerry's,
Larry's, etc., those "technical sailors."

Of course the ability to put up more sail in light air, and less sail in
heavy air, will make a difference, also.

:)

Steve Barnes sailing a Capri-16, #74, no name yet,
and selling a WWP-14, Popeye, #561, in San Diego.
OLDSURFDUDE