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Something about the fractional rig that I just don't get...

16642 Views 65 Replies 20 Participants Last post by GeorgeB, May 1, 2014

MedSailor

Discussion Starter · Apr 25, 2014

There's a concept that's been bugging me about the factional rig. I understand the advantage of mast bend, but the smaller foresail is also touted as an advantage with the main being "the sail that does all the work anyway".

But, wasn't the big deck sweeping and overlapping headsail supposed to be the thing that really mattered? All the club racers have huge overlapping headsails and the "slot effect" is supposed to help with speed. I've heard people say that the headsail is the one that does all the work and pointing...

These guys are fast right? How come they look like masthead boats with big overlapping gennies?

MedSailor

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Osprey 26

· #39 · Apr 29, 2014

My guess is most of our wind measuring instruments, wind tunnel experiments show only one kind of wind. If there is only that kind of wind there would be nothing left behind so to speak.
Sir Isaac was probably right in explaining how things work.
Yes some sails do catch better then the other some of that extra unmeasured wind.
Faster then wind speed is result of this phenomenon on ice boats and such.
Probably to simple to be any good.

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Osprey 26

· #61 · May 1, 2014

lancelot9898 said:
Very interesting discussion. There are many variables that come into play when making such a comparison that to me saying a fractional rig is better that a MH rig has little meaning. Fluid dynamics was not my favorite subject in college since much if not all is based on emperical data whereas I always needed to go back to basic theory to understand what was being observed. Thank you Mr. Newton. I should spend some time reading Gentry's articles as RichH suggests, but doubt if I could grasp the information. Look at some of the improvements and innovations in aerodynamics over the past decade. Large commercial planes (and even smaller ones) now have a vertical component on their wing tips to enhance performance. The AC series boats have a main with the head no longer pointed but now it has a long horizonal component. The stealth fighter with all its odd shapes was thought it would not fly efficiently, but yet it does.

As time goes on other improvements to get better performance out of fluid dynamics will take place and I'm sure that some will seem contrary to present day understanding. My 2 cents.

Oh, I really like that how is explained. Also like how dedicated professionals, and experienced individuals in general help us understand what going on with sails, wind power.
There is also lot to learn, and if questions from us not in same class so to speak probably can help.

In lab type wind tunnel tests we do get basic knowledge. In real world it isn't that simple to get 100% same results all the time.
Wind instruments have some inertia and show more stable wind speed.
My guess is there are all kind of speeds in that spectrum like in white light.
Ice Sailboats with little resistance use those micro speed bursts to go
3-5 times faster then indicated wind speed.

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