On Tue, 16 Sep 2003 23:52:22 -0700, in message

"Evan Gatehouse" wrote:


"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.

You need to check the page again. The recommendation is based on the
size of the *foretriangle*, not on the size of the headsail. My
*foretriangle* is just over 300 square feet and the Lewmar 46s are a
good match for the loads all the way from the blown out 150% down to
what some of my chums refer to as my "cocktail jib" (short hoist for
about 80% of the foretriangle area).

The usual formula for sheet loads is

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

Both the sheet load and the driving forces will scale with V^2. If one
assumes that one will shorten sail at higher wind speeds to maintain
similar power levels, then the sheet load will remain similar as the
wind speed increases. If one then assumes that boats will carry
foresails with size being a similar fraction of the foretriangle at
similar wind speeds, then the loads will scale with foretriangle size
from boat to boat.

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.

Probably. Note that a 505 square foot genoa would be 150% of a 335
square foot foretriangle and match the recommendation pretty closely
with a 56:1. OTOH, the 505 square foot storm jib of a MUCH bigger boat
would carry much higher loads and require more mechanical advantage.

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

9.81 N is the force of gravity on a 1 kilogram mass near the earth's
surface, so 1 N is the weight of a mass of 0.10 kg or 0.22 lbs.

Ryk

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