[Osprey 26]

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.

 

[tommays]

This is interesting due to the long term Success of J29s in this area right up to NOW

It is more so because despite all the variation's the MH/outboard is the most popular and sought after model in this area

 

[Stumble]

So I was doing some reading last night and this conversation popped into my head. Go take a look at the current generation of C class catamarans. These race in a pure development class, and the only restriction on sails is maximum sail area. Right now they are all using high aspect wing cat rigs. There isn't even a jib to be seen. And some of these teams have massive amounts of money to throw at the problem since the. C cats are test beds for large boat programs (Americas Cup, IMOCA, maxi cats, ect).

 

[Shockwave]

Flex? The backstay? Or the over anxious guy on the checks trying to drive the spar through the bottom of the boat?

I like in line rigs, even with their short comings, versus swept spreader rigs. In line rigs have a larger range of movement allowing better draft depth control but for a cruiser a swept spreader rig is probably better.

It depends on the boat and the rig. Generally the backstay is just to play the top of the main, and it leaves the jib tension alone. But then you have a lot of fractional rigs without backstays with just runners, or some that don't worry about anything but prebend.

This is where rig design gets really fun. Since you can design a boat without needing to absorb all the backstay tension you can design a different hull. The J-35 for instance sailed best upwind with about 3500psi of backstay pressure. But the boat wasn't designed to take this much pressure and the hull would start to flex. On the fastest boats reinforcing the hull became necessary to offset the mast pressure.

 

[Stumble]

Shockwave,

On the J-35 I raced on we carried so much backstay pressure (on top of 16" of prebend) that the hull would actually flex. Based on our measurements the boat shortened by about 2" and widened by 4" (I think, I don't remember the exact measurements anymore). To counteract this we rigged in internal wire support system that tensioned the whole boat to prevent it from flexing.

This is an extreme example of how to get enough forestay tension on a MH can cause all sorts of weird spiraling issues.

 

[GeorgeB]

Backstay tension until the boat bends is pretty standard SOP. To calibrate the Cal 40, we stretched a line between the pulpit and pushpit. Marked the intersection with the mast and applied tension until the line "sagged". 2,000# is our "beating - heavy air" setting and our max setting is 2,500#. We also completely slacken off the back stay for downwind work.