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Main halyard winch, 1sp. or 2sp?
Here is where I got the formula on the Harken site. About 2/3 down the
page: http://www.harken.com/winches/wnchpower.php It is also in Brion Toss's Riggers Apprentice on page 42. (Almost verbatim from the harken site.) OTOH, when you look at the tables a 56 or 64 is the recommended size for a 500 sq ft foretriangle. I wish to heck I knew what a Newton is. All the really authoritative modern texts are metric! -- 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 |
Main halyard winch, 1sp. or 2sp?
On Tue, 16 Sep 2003 19:41:47 -0400, Glenn Ashmore
wrote: Here is where I got the formula on the Harken site. About 2/3 down the page: http://www.harken.com/winches/wnchpower.php It is also in Brion Toss's Riggers Apprentice on page 42. (Almost verbatim from the harken site.) OTOH, when you look at the tables a 56 or 64 is the recommended size for a 500 sq ft foretriangle. I wish to heck I knew what a Newton is. All the really authoritative modern texts are metric! Hold a good sized apple in your hand: that's a force of 1 newton you're holding it up with - a little under a quarter pound. Brian W |
Main halyard winch, 1sp. or 2sp?
On Tue, 16 Sep 2003 19:41:47 -0400, Glenn Ashmore
wrote: I wish to heck I knew what a Newton is. All the really authoritative modern texts are metric! It's a brown, square little cake stuffed with Fig guts about 1/2" thick and cut square on two sides like it's made in one continuous tube and they slice it ever' so of'n. They also got 'em in Strawberry, Blueberry an' Raspberry, but I suspect the Fig ones'll always win out from the traditionalist buyers who are addicted......and my two parrots. Larry W4CSC 3600 planes with transponders are burning 8-10 million gallons of kerosene per hour over the USA. R-12 car air conditioners are responsible for the ozone hole, right? |
Main halyard winch, 1sp. or 2sp?
"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 -- Evan Gatehouse you'll have to rewrite my email address to get to me ceilydh AT 3web dot net (fools the spammers) |
Main halyard winch, 1sp. or 2sp?
On Tue, 16 Sep 2003 19:41:47 -0400, Glenn Ashmore
wrote: snip I wish to heck I knew what a Newton is. All the really authoritative modern texts are metric! Try.... http://www.savardsoftware.com/masterconverter/ ....a good little software converter that allows you to quickly change variables to begin to grasp the units of measure. --- Max and Hillary, sitting in a tree; Cay-eye-es-es-eye-en-gee. |
Main halyard winch, 1sp. or 2sp?
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 |
Main halyard winch, 1sp. or 2sp?
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 -- Unfortunately this address has been overrun by SPAM. If you want to be sure I see email from you, then please include the words "Ryk says it's OK" somewhere in your message. |
Main halyard winch, 1sp. or 2sp?
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Main halyard winch, 1sp. or 2sp?
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 |
Main halyard winch, 1sp. or 2sp?
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 |
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