I agree with Evan -- Harken is way off.

The formula Evan quotes is the same one I quoted above. As I noted,
it's been used by Skene (Kinney), Van Dorn, Henderson, Marchaj, and
many others.

The trouble with the Harken formula is that it doesn't specify a wind
speed. Since sheeting force varies with the square of wind speed,
that's a vital part of the choice of winch size. If you really expect
to carry a full foretriangle at 40 knots, then the Harken formula is
fine. That, however, suggests that at ten knots you'll be grossly
undercanvassed -- that you could carry sixteen times more sail than
you have.

Put another way, the difference between a 56 and a 66 is 18% in power.
Since the sheeting force varies with wind speed squared, a sail that
is easy with a 56 at 20 knots would require a 66 at 21.7 knots. Since
this is a very subtle difference, the only way to do this is for you
(Glenn) to do the math. Look at the rig you'll be carrying at each
wind speed, calculate the sheet loads with the Evan's formula and make
a decision.

Your naval architect can provide a table of her ability to carry sail
at various wind speeds up to bare poles at around sixty knots.
Beware, these are probably high -- my experience with several boats,
including Swee****er (Swan 57 by Sparkman & Stephens) was that we
never carried as much sail as they said we could. We were, of course
cruising shorthanded, not racing.

For my money, they are far better places to put money in a cruising
boat than in big winches. Dee (wife and crew for 37 years) would
agree, and she's the one who has to be perfectly happy reefing,
tacking, whatever, alone at night, in a blow, without waking me.

(I should add, however, that there are limits. The sailor who goes
out with grossly undersized winches and tacks by luffing while
sheeting, risks breaking the winch or ripping it out of the deck in
puffs.)

Jim Woodward
www.mvfintry.com

"Evan Gatehouse" wrote in message ...
"Glenn Ashmore" wrote in message
...
Here is where I got the formula on the Harken site. About 2/3 down the
page:
http://www.harken.com/winches/wnchpower.php

In this case I think Harken is just off. They use an example of a 300 sq.
ft headsail (nearly the size of the genoa on my last boat, a 30' cutter) and
conclude you need a 50:1 winch. I don't think so. The winch was a 2 speed
32:1 and was fine. Yes, it was a bit of effort in a stiff breeze - but you
could still wind it in.

The usual formula for sheet loads is

F (lbs) = 0.00431 A(sq. ft) V^2 (knots)

There are some frictional losses through sheet blocks but not that much,
perhaps 10%.

I think 56's would be more than fine for your 505 ft foresail. If they are
self tailers, and you use a 2 handled winch handle, they will be a breeze
for smaller crew members.

by the way in case you were not kidding:
1 N = .0981 kg i.e. about 0.1 kg force or about 0.2 lbs