MPX-11 Very Small High Power Trimaran

mr. paul b

all thanks in suggest a look back for history. some part here not right on this flashtri subject. i look to this after sleep.

 

Where you put bench seats now. boat still dangerous. have to much sharp points and edges all over. not know how it may sail and not a pretty boat to see. is soft design place that does not change so not a good boat.

designer have many boats of same kind and comes to complete boat after much testing on different shapes and success. i see no looking at different boat type in this design. is same from begin to now only make tiny bit longer. not strong boat idea at all.

explore many ways and you will see as i mean.

 

Doug,
You've ambitiously decided to put in a centreboard/mainfoil with three degrees of freedom. Canting, raising and gybing. While I question the practicality of all three (particularly in combination and without a very large budget!) I'd like to look at the gybing aspect in particular. If I recall correctly, you added the gybing functionality after concerns were raised as to the boat's ability to resist leeway. In your view, how would a gybing board do this on a foilborne craft? I question the effectiveness of this as a solution.
As far as I know, part of the merit of a gybing board is that by compensating for leeway by rotating the leading edge of the board to windward, the hull then makes a straight path through the water, reducing resistance. On your boat, where the the only hull in contact with the water is a short, splashing outer hull that presumably won't change its drag characteristics much with a small change in the angle at which it passes through the water how does a gybing board actually help? How is it meaningfully different to just heading up a few degrees and tightening the sheeting angles a little? Perhaps it helps when the main hull is in the water only?

I think the leeway problem is still there and that the addition or deletion of the gybing aspect of the board will do little to impact on this aspect.

 

MPX-12-board system

At this point, the boat uses a retracting canting and gybing board:
1- retracting allows beach sailing and transporting the boat with the board/hydrofoil in place.

2)-canting allows the small leeward component of hydrofoil lift at 10 degrees angle of heel to be 100% eliminated. It is still possible, if the system can be done in a satisfactory way, that the canting may be increased so that the main foil contributes to unloading the daggerboard-similar to "veel heel" in a monofoiler. First mentioned in post #8.

3) Gybing allows the bow to rotate slightly to leeward ,allowing the sheet(s) to be freed a little increasing speed. The "crabbing" component of drag from the ama is also eliminated. The net result is an increase in VMG to weather. If the cant angle is increased the gybing board may not be necessary.
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Notes:
a. the immersed board area of the MPX-12 is over twice that of the Moth but most importantly it is 17% greater than the Moth immersed daggerboard area
as a percentage of sail area. And that's because the Moth achieves some of its lateral resistance from the fact that the main foil contributes to partially unloading the daggerboard upwind when the boat is "veel heeled" 10-15 degrees.

b. Steve Clark uses canting, retractable, lifting boards on Aethon. The use of such boards on the ultra light C Class shows that their weight and "complication" is not a negative factor.

c. The Capricorn F18 Cat uses gybing boards, as does the 505 and several other dinghies.

d. mainfoil angle of incidence is adjustable(set and forget) and the altitude control system is unimpeded by the canting, gybing functions.

e. the downside of the daggerboard on this boat is that it is a surface piercing foil. There are numerous boats that function well to weather with surface piercing daggerboards/foils-among them Spitfire, Hydroptere, the Rave and others.

 

a: Steve Clark Aethon. the good on this boat comes now from what success? i read on this boat and it sail very small time. nothing strong to know in such small test period.

d: can more control parts be on flashingtri? little boat has many control part. soon boat not possible in sailing. is now not fun to sail with to many control part.

e: all boats told on this are trimaran with three foil parts in water. flashingtri only make two part in water against leeway. how you compare tri on list here with flashingtri?

 

If Im following this design... wouldnt the gybing board also significantly increase the risk of the foil ventilating? Presuming that the gybing board is going to produce more 'lift' to windward there will be a bigger low pressure zone that also comes right up to the water surface since the hull is flying. Also wouldnt a lifting foil be reducing the righting moment

 

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No. The gybing board doesn't produce significantly more lift-it produces the same lift augmented by slightly higher speed-its just oriented differently to the boat. Thats why a boat that uses a gybing board doesn't point as high as one without a gybing board-the bow rotates to leeward, the sheets are slightly slacked and the boat moves slightly faster-maybe. I don't think it would have any appreciable effect on the chance of foil ventilation.

Thread on gybing boards-read it all-particularly Speer Post #3 and others: http://www.boatdesign.net/forums/boat-design/gybing-daggerboard-5783.html
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PS-Glad you said what you did ,Cheesy. Otherwise I may not have reread that thread where Speer points out that as the bow rotates down it brings the daggerboard wake more in line with the rudder wake. Bethwaite says the same. That could potentially cause ventilation of the rudder in a set up like this.

 

Doug, the poor helm on Flashingtri is going to have his or her work cut out to operate all the twist grips, levers, rope pulling, not to mention the basics of sail trim and best course and watching for gusts and lulls and so on. Their eyes will going one hundred miles an hour, head bobbing, arms waving. elbows levering .... there is TOO MUCH stuff on this boat. Why don't you listen to the comments made here by many and simplify? It's only 12 or so feet long, a small boat - go back to basics. But no, you have a fixation with bells and whistles and this commentary is about as useful as flatulence against thunder.

 

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There is not as much to do on this boat as there is on a Moth and dozens of other skiffs and catamarans with two boards, two rudders, mast rotation control, main and jibsheet etc,etc, Most everything is automatic once the initial set up is made. I had more lines to pull on my Windmill in the 60's! Not only that but how do you know?? The boat is experimental, again: the boat is EXPERIMENTAL-I'm not even sure what systems would make it thru but I can guarantee that this boat will be exceedingly simple to sail when everything is tested and proven. You're exaggerating completely unreasonably, Gary. To the point you even make stuff up-pitiful. Some discussion when you and others simply invent problem areas......Gary, you probably haven't even read a thing I've written ,have you?? There is not a single lever or twist grip as part of this design!!!! You have to make stuff up,huh?

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So lets look at all these bells and whistles-where are they????
1- Mainsheet-single sheet for main and jib-mentioned earlier.Sheet comes from forward.
2- Dual extension tillers or single-owner preference(unless the "owner" chooses manual control which is unlikely to be offered in the first place. But I would like to try flying it manually.)
3- Vang? Outhaul? traveller?
4- Cant the board-probably automatic-owners preference. Gybing board,if used: automatic.
5-what else, Gary? Once the adjustments are made to the foil and daggerboard system it's all automatic.

 

Some fair comments in there Doug. Your notes deserve a response though:

a.) Probably the best point of your post but is it valid? Have you compared just the vertical area with the vertical areas? If so, then the moth figure is understated because it does not take into account the contribution of the lifting foil in resisting leeway. I think your understanding of windward heel focuses too much on changes in righting moment and not enough on the benefit of having a fully submerged foil contributing to resisting leeway. A portion of the lifting foil for the moth should be counted in the lateral area calculation and the effectiveness of this area should somehow be acknowledged because as a fully submerged foil it will be less likely to ventilate than the surface piercing foils you will be relying on. The late inclusion of commentary talking about canting the main foil beyond simply vertical seems like a band-aid solution that just adds even more complexity to a system that is already vastly more complex than your previous failed projects.

b.) Canting, retractable and lifting is not the same as canting, retractable, gybing and lifting with an articulated flap. You are proposing something much more complex. Invoking the name of a credible boat designer and builder to support your case only works if you are proposing something similar. You have previously put the failure of your last boat down to the flap control system having too much slack so your confidence in making the task much more complicated and fully expecting to succeed seems a little misplaced. Having failed to jump a little stream you are now proposing to pole vault over shark infested crocodile pit with your pants deliberately on fire. Is this sensible?

c.) Yes, other non-foiling boats using gybing boards. Are you making any point beyond this?

d.) It is very easy to write that a system works perfectly and that there are no problems. It is very different for that to be the case in reality. Have you even designed the mechanism at the foil top?

e.) I've not seen much evidence of the boats you mention actually sailing to windward very well. Can you substantiate your claims?

I don't really think brushing off Gary's comments on complexity by saying that the systems are automatic is really valid. Unless they are very simple, automatic systems have a habit of not working. Your proposed systems are the opposite of simple. I think you proposed linking the gybing board to the sliding seats, which is all linked to the ride height control at the top of the main foil which is all connected to the foil canting system, which can all be pulled out of the way to lift the main foil when approaching the shore. Any suggestion that this will be simple is simply ignoring reality.

 

I know this is off topic but speaking of simple have the windsurfer guys got on foils yet?

 

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Yeah, its off topic but:

 

Thanks Doug! The concept made sense......

 

Farting against thunder again - why do I do this? All I'm saying Doug, is make a basic simple platform - like conventional little tri, okay with planing amas but basic shape (what you've got in the dragon's tail is a disaster in the making) a simple but correctly designed daggerboard (forget about the gybing board/foil nonsense) and a simple but sweetly designed rudder, no foils, usual trampoline and a basic cat rig with rotating mast. A boat like this, with a large rig, will be a veritable little rocket. Then later, if you feel so inclined, although you would probably enjoy the boat so much you won't bother, you could introduce one at a time, a specialized refinement you have been brainstorming over here in such enormous amounts of thread space.

 

Aw shucks Gary I thought you meant this, from post #40:

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Kinda hard to get your "opinion" together ,huh? Not too cool..... Gee, Gary don't feel bad-you're not the only one who hasn't read the thread yet feels compelled to blurt out stuff that,well, doesn't make any sense. Have you even remotely looked at the current design crop of 12' trimarans? Do you know why they can't fly the main hull? Do you know why that is slow? Sure you do......