MPX-11 Very Small High Power Trimaran

Nothing as to hot air when to make self hero.

two smart men say build flashingtri and prove truth. mr. doug ignore strong comment.

i do not know why.

 

Foto show no change to flashingtri. must make better foto as to change place and then to show once more.

 

"Note: in a previous post some mention was made of scaling Flash Harry down to 14'. Directly scaled down it would weigh 54lb(114 w/crew) and have a sail area 97 sq.ft. So obviously some modifications to the hull(and/or its waterline position) and rig would have to be made to make the "scaled down" design viable at 14".

That is correct Doug. IF(?) I was going to build this boat the 3mm ply and glass hulls would be changed to near semi-circular in cross section but the deck beam would remain the same, that would increase buoyancy and lift the platform higher; also the bows would be reversed and instead of the simple conventional mast, would be changed to a small chord wing. On a very light boat like this, (with one crew) foil lift would be substantial so the platform would begin lifting even in light airs; wing mast would be 6.5-7m tall with a 300mm chord and sail area in una rig around 8m2. Also the single, simple, sheet 4mm ply beam, like a sort of triangulated box, would have some dihedral to lift the windward foil so to be only half immersed under sail power, for less drag. But all this conjecture is just conjecture - means very little - and I doubt Little Flash Harry will be built.

 

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This is a remarkably light boat. "IF" would it be a foiler or "foil assisted"?
Interestingly, if one uses the formula for lift and solves for the various loadings of Flash Harry on small foil with a 63412 section it becomes apparent why most foil designers DO NOT use fixed AOI fully submerged T-foils: with just small changes in wind pressure the CL(lift coeficient) appears to go right out of the drag bucket. That leads to the tentative conclusion that such a foil would have a low drag Cl for only one wind speed UNLESS crew movement made a difference(which it does) OR the angle of incidence of the foil was manually changed. I guess if there was a line painted on the leeward vertical foil the crew might know when and how far to move. This would only matter if the idea was to sail as fast as possible-basically moving to keep the foil in the drag bucket. I'm going to look into that a bit more. Doesn't seem fast as compared to an altitude controlled foil that would automatically adjust. With fixed fully submerged T-foils(Baigent "foil assist") there is no comparison to the MPX-12 at all:
1-far more crew movement,
2- more foils for the crew to handle,
3-not automatic like the MPX is,
4- will not fly the main hull except just before a wing-dinger of a crash,
5- diagonally unstable when main hull gets light(close to flying)
6- it appears to me that if the crew weight was far enough to weather of the floating main hull to equal or exceed the rig induced load on the lee foil it could pop out and crash back in a cyclical manner. If it happened it would probably be easy to fix with crew movement.
7- if this type of foil system(fully submerged fixed t-foils) reduced the main hull wetted surface at all it wouldn't be until fairly strong winds-whereas the MPX system reduces main hull wetted surface to zero in very light air and zero for the devils tail ama as well in the lightest air. Not only that but the faster the MPX goes the LESS the load on the foils!

 

if to scale so make as flashingtri i take start idea as foto on page.

 

Doug, if you look at the jpeg Eraind44 posted above, those are the type of waves, although smaller in this case, where 6m Harry would crash. mainly because the una main was not reefed and the boat was way overpowered and sailing too damned fast. I'd like to see Flashing tri in such waves or Trapped under wing - I think it would really live up to its name.
On Harry, in fresh winds, you sit as far to windward as possible but you don't move in and out but play the uncleated traveller continually. In moderate and average sea conditions, the boat never crashed; and has given me decades of great fun sailing ... all that I wanted from it. In tougher conditions (which the boat was never really designed for) you expect a few problems.

 

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Sure Gary- just outstanding-my congratulations.

 

Doug,

I have been following this thread from the begining, and I like your concept and ideas. But I am a bit perplexed at the logic behind the T-foils and the planing amas. Perhaps I missed it somewhere but if your intent is for these foils to lift the main hull out of the water when at design speed, and counter the heeling forces with the crew's weight, than why do you need the amas at all? Just save weight and cost and eliminate them.

If the amas are to counter the heel, than countering the heel will lift the main hull out of water, and you would not need the T-foils under the main hull. It seems to me that if you size and position the planing surface on the amas to balance the heeling forces, you would not need to lift the main hull out of the water, since you will be riding on the planing surface of the ama only.

ON the fastest modern tris they reach their best speed when flying the main hull with only the lee ama in the water. Your design should work the same way, all of the forces balanced by the lee planing surface. So why would you have lifting foils under the main hull? if your intent is to balance the heeling forces with the crew weight, than why do you need the planing amas? If the ama is there to counter the heel, than why do you need the T-foils?

Perhaps I am missing something here, but it seems to me that you have put some concepts together that are not entirely thought through in terms of how your various design elements are going to work together. The whole boat has to work together as a system, and I do not see how that is supposed to happen here. Reminds me of one of my first engineering jobs working for a man that built race cars, he had this idea of building a mid engine race car (to have good balance and good handling), but with front wheel drive for good traction. I had to point out to him he would be sitting at the starting line frying his front tires because there would not be enough weight on them to get any traction. He had not thought through the whole operation the race car until I explained the dynamics of it for him, and he fortunately abandoned the idea.

If I were building this I would leave out the T foils, and put one small dagger board in each ama, and one small simple rudder on the rear of each ama. So when at design speed the only thing in the water would be the planing surface on the ama, and one small non-surface piercing dagger board, and one small rudder. That should have less drag than using such large T-foils. Than when in displacement mode at lower speeds you would have two dagger boards and rudders in the water for better control.

To my engineer's eye, those T-foils would have to be made of some pretty costly materials to be anywhere near stiff enough to be able to carry the loads and keep the boat controllable (IOW, they look like real "flexy flyers" to me) and I think they are much larger than you would need to lift such a light boat out of the water. Have you done actual lift and drag calculations of the foil surfaces?

Could you please explain why you have planing amas AND lifting T-foils under the main hull? I am not getting the logic here. It would benefit the design to keep it as simple as possible.

 

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Thanks for your comments ,Petros. You certainly have missed a lot. When you can please read posts 2, 29,85 and 87.
1) The hydrofoils princible job is pitch control. Pitch control is critical as is a well controlled heel angle for the planing ama to be effective and at the same time to be low to no drag in light air and minimal drag when planing at the most efficient planing angle which is 100% maintained by the hydrofoils(and adjustable as well).
2) The foils are designed to lift the boat off between 6 and 8 knots of boat speed-about 5 knots of wind. With the 16.5' beam without the foils the thing wouldn't fly the main hull until over 15 knots of wind or so. Most people sail in 10 or less so it is essential to have the boat perform exceedingly well in those conditions. In up to 10 knots of wind there is no need for the amas to touch the water-after that the leeward ama gradually loads up until it is carrying most of the weight. As that is happening the foils unload reducing their drag considerably. The reserve "power" of the foils is always there for pitch control. This allows the wetted surface of the main hull to disappear early and the drag of the foils to drastically diminish as speed picks up. The beam is necessary to generate the tremendous righting moment required to sail fast in a breeze.
3) A side benefit of a wand controlled main foil is that not only will it lift vertically but once the boat starts to heel beyond the "set" altitude(heel angle of 10 degrees) the wand causes the flap on the main foil to go up generating downforce(extra RM) as necessary. This allows a very wide crew range since a 120lb kid would be able to sail with the same maximum wind pressure as the heavy crew because of the extra RM from the downforce of the foil.
Response of the altitude control system is virtually instantaneous. Some of the early posts in this thread discuss other boats that use an altitude control system for VERTICAL Lift and DOWNFORCE-like the Rave and Hobie Trifoiler.
4) This system is critical for the performance of the boat-without it in light air or heavy air it would be a dog. All of it works together and is inter-related-without one part of the system the whole thing is useless.
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I hope this helps. Read the stuff above if you haven't already and if you have any further questions I'll be glad to answer them.

 

so the main foil will generate down force to keep the heeling angle at optimum, when in stronger winds?

That means you will have large induced drag on both the foil and the ama, the ama now has to generate enough lift to counter the down force on the foil, to generate the righting moment. It would be easier I think, and less drag to have the seats slide further out on the beams. No additional drag, no additional lift required on the ama.

 

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If you read some of the stuff already posted you'll see that at no time does the downforce exceed the RM at max wind pressure(above max wind pressure it is the crews responsibility to depower or reef as on any other boat) The point at which the boat needs to be depowered would visible to the crew in terms of speed shown on a speedometer and/or continuous flap deflection beyond a marked point(marked on a simple indicator at deck level) and/or any heel beyond 10 degrees that is sustained. After testing the precise limits will be known making it easy for the crew on any subsequent production boats. There is ,generally, only downforce when the boat is sailed by a light crew or in a gust with the max weight crew. As to induced drag, at no time is the Cl(lift coefficient) outside the drag bucket of the foil. And since the ama is designed for max load it is operating efficiently at all times-that is the point of the foil control of running trim angle.
The point of the design is to allow a 12' X 16.5 tri to function efficiently throughout the wind range. It appears as though it will.

 

Doug, it appears you have built a small model of this "trapwing" prototype and explained a lot of technical details.

Considering the small size of the craft I would say it's high time you built a full scale prototype, test it out and post some videos to Youtube. Many would like to see how it performs.

 

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Wrong thread-but I agree 100%.


Trapwing thread is here: http://www.boatdesign.net/forums/sailboats/design-challenge-trapwing-deck-ballast-12-22-a-29610.html

 

not wrong thread. maybe wrong word and is easy for wrong word. also trappingwing foto on page for sail talk and so more easy to make wrong word.

still is the talk about build and then no build will be for truth here.

 

confused mr. doug. you see part at mr. petros where say he is engineer. are you engineer mr. doug. is a place as to thinking on flashingtri and you are engineer with power. mr. petros have more to say when engineer than are you i think. maybe listen and no talk is good with you.

please to say more mr. petros. we listen.