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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Ryk wrote:


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 foretriangle is what we are talking about. Acording to that formula
your 300 sq ft foretriangle needs a pair of 52s. My I = 58.8 and J =
17.25 so my foretriangle is about 507 sq ft. The formula comes up with
80+ which is obviously out of line.

I think the problem is the 6 factor. It is supposed to be a combination
of 30 knots of wind and all the friction load. It must have been chosen
by a winch salesman. :-)

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Holy Cow. By that formula, the boat I race on with the 660 square foot
foretriangle (and it's a 12 ton boat to boot with lots of stability and big
loads) has winches about half the required size. We race with old
Barient 52s, and while short tacking with the #1 requires us to swap
out grinders on occasion, I don't think a 110 power ratio is what the
boat wants. I'd say something in the 60's would be better than what
we've got (the Barients were the biggest thing going when the boat
was built).

Use the formula Evan gave you (assume full foretriangle at about 30
knots) and go from there. Use a 35 pound load on the winch handle.
That gives you a 56 which is probably in the ballpark.

"Glenn Ashmore" wrote in message
...


Ryk wrote:


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 foretriangle is what we are talking about. Acording to that formula
your 300 sq ft foretriangle needs a pair of 52s. My I = 58.8 and J =
17.25 so my foretriangle is about 507 sq ft. The formula comes up with
80+ which is obviously out of line.

I think the problem is the 6 factor. It is supposed to be a combination
of 30 knots of wind and all the friction load. It must have been chosen
by a winch salesman. :-)

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Wed, 17 Sep 2003 23:02:56 -0400, in message

Glenn Ashmore wrote:



Ryk wrote:


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 foretriangle is what we are talking about.

and the post I was responding to was talking about "They use an
example of a 300 sq. ft headsail (nearly the size of the genoa on my
last boat, a 30' cutter)"

Acording to that formula
your 300 sq ft foretriangle needs a pair of 52s.

The 46s I have are good, but I sure wouldn't complain if a pair of 52s
appeared on my deck by magic. It's quite probably the racer in me that
just likes big winches.

My I = 58.8 and J =
17.25 so my foretriangle is about 507 sq ft. The formula comes up with
80+ which is obviously out of line.
I think the problem is the 6 factor. It is supposed to be a combination
of 30 knots of wind and all the friction load. It must have been chosen
by a winch salesman. :-)

It's probably also an issue of how you would likely sail the boat. If
you want to carry a 150% genny until performance would improve by
shortening sail and don't want to luff in order to trim, then you
probably would need the 80+ to stay down to the 35 pound load. You
could reduce the requirement dramatically by accepting a modest
performance hit in either of those areas and that could make a lot of
sense as a cost trade-off for cruising. Also, on a bigger boat it is
typically easier to get right over the winch, getting full use of both
arms and shoulders to raise the applied load on the handle, not to
mention moving up to a 12 inch handle.

Still, if money were no object, wouldn't a pair of 77 three speeds
suit your application (and the winch salesman's commission
account ;-) )?

Ryk

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