TexasPhil Posted August 3, 2003 Posted August 3, 2003 Does anyone know how much force is exerted on the sail, mast, and stays? Quote
SeaEagle Posted August 4, 2003 Posted August 4, 2003 Ummm TexasPhil... It might just depend on how much wind there is Quote
Guest Anonymous Posted August 4, 2003 Posted August 4, 2003 In a nutshell, NO! :-) Someone that is really into the math might give you an answer (not me), but I would suspect the variables would have to be given for a particular situation. Any force will change due to the direction it coming from, how strong, direction of boat, length of lines, boat speed at that time, etc. etc.. I would suspect too, that if you are trying to figure out when your rigging will "fly apart" you would need all the particulars (fairly exact) of the standing and running rigging and give an exact scenario,as to wind speed, direction etc...etc.. even this, would only give you an estimate, as the type of wood used in your mast, it's moisture content, any compression factors would all have to be taken into account... I think if I have read your question correctly, you would really have to narrow it down, before you would get an honest reply... I did do a little search on the matter and do to my own mathmatical limits I don't think I'd ever really ruminate on the subject past Bernouilles equation :-) page 6 of the following text/quiz might give you direction if you are so inclined... http://www.maths.usyd.edu.au:8000/u/david/MATH2010/tutorials/tut7.pdf If I have misread your question and what you are asking I am sorry, hopefully someone else will chime in to help you narrow down your quest... good luck.. Bill Quote
Charlie Jones Posted August 4, 2003 Posted August 4, 2003 The loading on sails and rigging can also very much depend on the boat type. For instance, a multihull has far higher loadings on rigging from the wind than a monohull does, since it does not heel to the wind- the boat is much "stiffer". That's why they carry so much heavier wire size for size than a mono hull boat does. Conversely a light, round bilged monohull with a fin might heel away from the wind far more readily, giving far less loading on the sails and rig. So there are many many things that can affect the answer- as is often said on the Trailer Sailor board when questions of this nature come up- It depends Quote
TexasPhil Posted August 4, 2003 Author Posted August 4, 2003 Bill, Wow, what a mathematical solution... I am afraid that my math skills have become a little rusty over the years so it might take a while to figure that one. Charlie, Very interesting point on sail type and hull type. SeaEagle, What can I say.... duh! Actually, more so than a mathematical formula, I was wondering if anyone has measured the forces somehow. As for the stays, I can think of two ways to test them: the first is to put some type of gage in between the stays and the boat, this would require shorter stays, so it is not very practical. The second is a gage that attaches to the stay and measures how tight it is. Then you can calculate the force on the stay by how tight it is. I am interested in any other methods that can be used to determine these forces, especially on the other components. My main curiosity is the ratio of forces exerted on the mast vs the stays. I am also curious how much over-built the rigging is, compared to what is required. Or, put another way... when will the rigging fail, and what is most likely to fail. Does the sail rip apart before the mast and stays? do the stays break? etc. Which boils down to: what is the wind speed that will destroy a full sail. Specifically, I am talking about the Stevenson's Weekender. I have not heard many reports of these components failing. But, since I am increasing the sail area by 26%, I wanted to make sure that this would not be a problem. If I need to beef it up, what is the critical component or components that require some additional strength. I hope this clarifies my question. Quote
Russell Sova Posted August 4, 2003 Posted August 4, 2003 Hey Tex, Why aren't you helping George clear brush? You can find this info in Royce's Sailing Illustrated. The pressure is figured by wind speed and sail size in sq.ft. ; for rexample on a day when winds are force 3 on the Beaufort scale, 8 to 12 knots the forces are .16 to .33 lbs. per sq. ft. The pressure increases exponentially as you sail in ever windier conditions. At a Beaufort scale 5, winds 17 to 21 knots you would experience pressure of .96 to 1.4 lbs. per sq. ft. Since you need a 10 to 1 ballast ratio a 100 sq. ft. sail area at 21 knots would experience 140 lbs. pressure centered several feet above deck at the heeling arm and you would need 1400lbs. ballast to keep it from heeling, ballast in form stabilty like a weekender/vacationer counts, too. Oh if I could just type without mistakes!~ Quote
Knut Posted August 4, 2003 Posted August 4, 2003 Phil, as far as I am able to evaluate the situation I think that the rigging on a standard Weekender is widely over-designed. There is nothing wrong in that, but mast and stays are loaded very little as can be demonstrated by the behaviour under wind pressure. If you pre-tension the stays somewhat (far from fiddle string level) you will see that the leeward shrouds are not getting slack even under strong wind an full sail-area. However, the main reason for my claim is that the Weekender is a dinghy. The dimensioning factor is how much sideways sail- and rig pressure it takes to knock the boat over on the side. This is far far less than what the rigging can take, may be with a small reservation for a worne, weak or wrongly tensioned mainsail, which could rip in a sudden gust. Quote
Charlie Jones Posted August 4, 2003 Posted August 4, 2003 Yes there are things to use to check the tension on shrouds, Called a "LOOS guage" You can get them from West Marine among other places. I've used them to pre-tension rigging on racing sloops, and to check the rig tension on other boats, including my 21 foot sloop. Hnady gadget, but not real cheap Quote
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