In my perpetual quest to improve and upgrade Sine Qua Non I have read, like the rest of you, countless specifications and reviews of different pieces of hardware. Everything from ropes to rope clutches, blocks to travelers have references to maximum loads and breaking strength. I sail a CD27 with a mainsail somewhere in the area of 170 sq feet. Stresses on that sail vary according to wind conditions but what I want to know is how do I calculate or where do I find statistics that tell me how much stress in pounds is being generated that has to be handled by mainsheets, main halyards, reefing lines, mast base blocks, deck organizers, rope clutches, cleats.....you get the picture. When I look in a catalog I really don't know if a smaller size is sufficient or if I need a larger size of the same hardware for my boat. They all say something like "for boats up to 30 ft. Or Mid range or Large boat. Well, what does that mean? My boat is 27 ft and displaces 7500 pounds. There are boats 27 feet that displace 4000 pounds and may have significantly larger or smaller sail areas. I usually wind up buying mid range hardware but does anyone have a more "scientific" or exact way to figure all this out?
Thanks,
Warren Kaplan
S/V Sine Qua Non
Cd27 #166
Setsail728@aol.com
Loads on Hardware
Moderator: Jim Walsh
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Neil Gordon
Re: Loads on Hardware
>>My boat is 27 ft and displaces 7500 pounds. There are boats 27 feet that displace 4000 pounds and may have significantly larger or smaller sail areas.<<
See an engineer for a scientific answer. <g>
For practical purposes, the sail areas on 27 foot boats will be comparable, as compared, for example, to sail areas on 40 footers. Stress loads are a function of boat size, sail area and sea conditions, for the most part, and not the weight of the vessel. There's been lots of discussion about this in relation to anchor size... they always conclude that loads are a function of boat size rather than weight. By the way, that's not true of self steering gizmos, where the power of the unit needs to be beefed up as the weight goes up.
If you want to feel safe, pretend your boat is a bit bigger and size accordingly.
Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167
cdory28@aol.com
See an engineer for a scientific answer. <g>
For practical purposes, the sail areas on 27 foot boats will be comparable, as compared, for example, to sail areas on 40 footers. Stress loads are a function of boat size, sail area and sea conditions, for the most part, and not the weight of the vessel. There's been lots of discussion about this in relation to anchor size... they always conclude that loads are a function of boat size rather than weight. By the way, that's not true of self steering gizmos, where the power of the unit needs to be beefed up as the weight goes up.
If you want to feel safe, pretend your boat is a bit bigger and size accordingly.
Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167
cdory28@aol.com
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John Vigor
Re: Loads on Hardware
Warren:
You can make a rough estimate of the strain on a jib sheet by squaring the wind speed in knots and multiplying the answer by the sail area in square feet. Divide the result by 232 and you have the approximate pull on the sheet in pounds.
Thus, a 200-square-foot jib in a 20-knot breeze generates a pull of 20 x 20 x 200 ÷ 232 = 345 pounds.
This formula is one of many concerning the power generated by sails, etc. in two of my books, "The Practical Mariner's Book of Knowledge," and the "Boater's Handbook." Both are published by International Marine. I don't make a habit of promoting my own wares on this board, but with your enquiring mind, it sounds as if you need them.
John Vigor
CD25D "Jabula"
jvigor@qwest.net
You can make a rough estimate of the strain on a jib sheet by squaring the wind speed in knots and multiplying the answer by the sail area in square feet. Divide the result by 232 and you have the approximate pull on the sheet in pounds.
Thus, a 200-square-foot jib in a 20-knot breeze generates a pull of 20 x 20 x 200 ÷ 232 = 345 pounds.
This formula is one of many concerning the power generated by sails, etc. in two of my books, "The Practical Mariner's Book of Knowledge," and the "Boater's Handbook." Both are published by International Marine. I don't make a habit of promoting my own wares on this board, but with your enquiring mind, it sounds as if you need them.
John Vigor
CD25D "Jabula"
jvigor@qwest.net
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Warren Kaplan
Re: Loads on Hardware
John,John Vigor wrote: Warren:
You can make a rough estimate of the strain on a jib sheet by squaring the wind speed in knots and multiplying the answer by the sail area in square feet. Divide the result by 232 and you have the approximate pull on the sheet in pounds.
Thus, a 200-square-foot jib in a 20-knot breeze generates a pull of 20 x 20 x 200 ÷ 232 = 345 pounds.
This formula is one of many concerning the power generated by sails, etc. in two of my books, "The Practical Mariner's Book of Knowledge," and the "Boater's Handbook." Both are published by International Marine. I don't make a habit of promoting my own wares on this board, but with your enquiring mind, it sounds as if you need them.
John Vigor
CD25D "Jabula"
Thanks for that VERY useful information. At least now I can get a rough estimate of what forces I may be dealing with and I can choose my hardware with enough reserve to handle extreme conditions if I get "caught out" No need to apologize for mentioning your books. As fate would have it, not 4 hours ago I finished reading your piece about taking a Catalina 27 to sea in Good Old Boat. I then clicked onto Amazon.com and ordered Twenty Small Boats..... I see you sail one of them, the CD25D. Thanks again
Warren Kaplan
S/V Sine Qua Non
CD27 #166 (1980)
Setsail728@aol.com