Trimaran lifting foil alternative

Discussion in 'Multihulls' started by kiwi_bob, Aug 27, 2011.

  1. kiwi_bob
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    kiwi_bob Junior Member

    Thanks for the info guys - I guess that curved foils are probably the rolls royce approach but very hard to make and retrofit (and heavy) and I'm looking for the next best thing. The problem I have with J foils and the fixed angled foils on KER CADELAC (and banana foils with tiplets) is that they are always there - even in light winds when not required/wanted and dragging - I guess you can remove the J foils on a light day but only from underneath the boat which is a PIA - it's not a soln for all conditions you may encounter in a single race - my guess is that the foil you want when the tri is moving at 6 knots isn't the same as the one you want when it's moving at 16 knots...

    See my primitive pic for what I'm thinking about - I guess it is closest to the DSS pic doug posted (but it wouldn't be dynamic at all). The surface effect (2.5 chords business) you mentioned if it exists is probably the most worrying aspect. If you went for very narrow high aspect foils it might minimise that effect (by minimising chord)?? I guess you could have multiple small chord foils sticking out stacked on top of each other like one of those crazy swiss triplane designs going around... Moving crew decisively could help to ensure the the foil is either fully out or deeply in? Thoughts??

    An additional bonus is everyone would think twice B4 luffing you in a race if you have big spikes sticking out the sides of your floats :).
     

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  2. Doug Lord
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    Doug Lord Flight Ready

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    Dynamic Stability Systems(DSS) refers to the fact that when the foil is deployed and the boat is moving the foil generates vertical lift that adds righting moment to the boat. Your foil is identical to that. I'd think it would be far better if you had the thing retractable or just put it on the inside if it won't retract. Having it on the outside does something no other foil configuration does: it adds RM outboard of the ama CB which moves the center of lift(buoyancy + foil lift) outboard as if you increased beam. Other foil systems either have the foil lift at the ama CB( T-foils) or inboard of the CB( some J-foils, angled straight foils and curved foils) which reduces RM slightly.
    Design is critical unless the foil can be easily moved and the angle of incidence easily changed during the testing. Testing without significant design work is a bit difficult with a foil that is going to lift a lot of weight-so I guess that is your first design decision, along with whether or not the main hull will fly etc. The more careful and complete the design the less likely grinder based surgery will be necessary.
    And you might contact Hugh Welbourn if you're serious-- I would bet he'd help a great deal if he thought the project was worthwhile. That would save you a bunch of time and money....
    PS- what you'd be doing is very experimental but with Mr. Welbourns help the chance of it working right the first time goes up considerably. And you would be doing leading edge development that could answer all the questions raised earlier as well as, potentially, doing a great service to multihull design and development. However, if he is not interested you might consider just going with a more "normal" solution unless you can commit a lot of time to development.
    At any rate, good luck!
     
  3. Gary Baigent
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    Gary Baigent Senior Member

    Doug, I think you're missing my point, which is: the Nacra foils have slight curvature, could almost say they're the same as straights, therefore no other dagger foils (except rudders) are required, so they will go to windward ... while Farriers et al, HAVE to carry a central dagger ... otherwise they'd go sideways because the sharply curved foils would be near useless beating on their own.
     
  4. kiwi_bob
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    kiwi_bob Junior Member

    OK but I would have thought adding to RM (and moving the center of lift forward a bit) when the boat is hard pressed would be a good thing? It should allow you to push harder for longer and ultimately give you a higher and safer top speed - that is my aim.

    Re DSS yes the effect is the same but I thought you can't call a fixed foil "Dynamic".

    My thinking on this was to put the idea out there and see if it had been done before - it's unlikely that it hasn't been tried and rejected B4.

    If it is in fact a new idea and the consensus is that the idea has some merit then I'd just attach a good strong mounting plate to the outer side of the float (directly beside the main beam so I have a handy bulkhead etc) and do practical experiments from there - I can commit considerable time and effort if I choose and I like "mucking around with things" to try something new. My fellow racers will no doubt point and laugh but that's OK.

    I don't know Mr Welbourne, does he patrol this forum?
     
  5. Doug Lord
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    Doug Lord Flight Ready

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    I think we're saying the same thing ,Gary- more or less. The curved foil can be retracted to the point it develops ONLY lateral resistance if it is designed for that like the NACRA or the Tantra II foil, or my SRT foil or USA-17's foil(s) which is halfway between the Nacra and the Farrier foil. My point was that all curved foils are not the same and can be designed precisely for the requirements of a particular boat.

    This was your original post saying that curved foils don't develop lateral resistance:

    And my response that not all curved foils are the same-they are designed specifically for the boat and can develop lateral resistance and vertical lift to the degree required:



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    Pictures: L to R- 1) illustration showing how vertical lift can be eliminated without affecting lateral resistance, 2)-NACRA curved foil that develops significant vertical lift with foil fully deployed but that lift can be almost eliminated leaving just lateral resistance by retracting the foil a bit, not "almost the same as straight", 3) USA-17 that used curved foils for vertical lift and lateral resistance-no daggerboard, 4) My SRT foil that is optimised for vertical lift using a short not retractable straight section that also allows vertical lift to be eliminated to one degree or another by retracting the foil AND develops significant lateral resistance.
    IMP: curved foils allow the angle of incidence of the lifting portion of the foil to be adjusted for the conditions without affecting the lateral resistance portion of the foil at all. No other foil configuration allows this*.
    * CORRECTION: Gary's angled "J" foil has a horizontal lifting surface-that surface can be adjusted for angle of incidence similarly to the way a curved foil is adjusted.
     

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  6. Doug Lord
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    Doug Lord Flight Ready

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    They call it Dynamic Stability System because the stability is only gained dynamically.

    ===============

    That is the whole point.... And an effective DSS type foil would add RM whereas other foil systems don't. But proving that DSS can work effectively on a multihull will take serious work but the rewards could be phenomenal.

    --
    Bob, because you're new to the forum you can't send or receive PM's yet. So send me an e-mail and I'll give you Hugh Welbourn's address. Or you can google Dynamic Stability Systems ........
    ---
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    You're almost right Doug in theory and for race boats. Gary, who has scale 1:1 experience is sadly right.

    In the reality of small foiler trimarans for cruising a straight foil is largely enough. The foils of Ker Cadelac ( 21 meters long...) were made with laminated cedar covered with glass and reinforced with UD carbon. I'm very sure because I was there...And that worked very well. Those made entirely in carbon broke like glass (in 1984 experience of carbon was small...) but those in wood/glass and a bit of carbon had enough flexibility to dissipate the energy and lasted a very long time.

    Curved foils are "*******" complicated to make. First engineering as you will have a curved spring so try to imagine the problems of vibrations and twisting, second the precision needed for the foil (a good laminar one with very little tolerance under 2%, the nose is primordial) and the boxes.
    That needs a very precise mold on a male plug made by CNC, and fabrication of the foils is not simple at all .
    The price for just a pair is pretty high...so high that a certain number of race boats share the molds of the foils to keep the costs down. Small ones are almost as expensive.
    Easy to dream about, big money needed to make it.

    So coming back to a small cruising foiler tri, relatively affordable, straight foils work pretty well and the realization is possible by a good amateur with some experience. The foils slide in the boxes like any daggerboard. In small weather or for beaching there are up, and going down as you need it, you can get the amount of sustentation you want. The system (a few pulleys and strings) is simple and straight. The horizontal foils won't be efficient: sucking air.

    The true problem with tri foilers with small amas is the rigging...and the rail for the main sail. Not a lot of places to put the chainplates. Look closely at the pics of Ker Cadelac (and similar other foilers) mast and rigging and you'll understand. For me it's the main draw back of a style of tris I'm very fond of.

    Happily on small tris the rigging problem can be solved without complications, and the foiler tri can be advantageous for an amateur construction. One main hull, one big arm (surprisingly "useful" with its internal volume), 2 "small simple amas. As the surfaces are smaller than on a big ama tri it's easier to keep the weights down without need of expensive methods. Less work to make it, far less material. Very good mean speeds and very sweet on sea. And they are beautiful!
     
  8. Samnz
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    Samnz Senior Member

    I think the main problems are where to position it on the topsides. If its too high it wont work till the float is under water. If its too low it will collect every wave when its not supposed to. It will often be dragging on the surface creating drag but not lift. The angle of the foil will also be very hard to determine as the boat might heal up to 20+ degress when pressed which would suck the boat to leward like a backwards asymetric foil?
     
  9. kiwi_bob
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    kiwi_bob Junior Member

    The problem seems to be you want it in or out of the water but not half way in between. As the tri heats up what is the crew movement regime? Something like:

    1. Light wind: Crew forward and central
    2. Medium wind: Crew forward and leeward (to attempt to get the main hull out)
    3. Heavy winds crew back and to windward.

    Is that correct??

    Between 1 and 2 there should (or could) be a dramatic increase in the weight on the lee float - if you position the foil correctly and hold the crew weight central then put em to leeward all at once then you could maybe avoid having the foil in the "transition zone".

    Sam, Kiwi_bob = Dean - I was just dwelling on this and pondering putting a mounting plate in place when I'm refurbishing the floats - first thing I wouldn't have any foil at all - this is for my "phase 2" development when I get sick of you powering past with your monster floats :). You know how I am somewhat worried about going over the handlebars...

    I'm also going to be limited in width by the rule so I may not have space for anything big enough to be effective too, will know that in a week or so when I have the beams finished and can experiment with floats angle etc.
     
  10. Gary Baigent
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    Gary Baigent Senior Member

    Doug, the image of BMWO (no main hull dagger) is of her lifted windward foil: I'm sure her working leeward foil would be well to right down, providing important lift and lateral resistance (her foils are lightly curved, not like your tight versions) BUT in stronger winds with your design, you're going to require plenty of lift with that hard working leeward foil to keep the float up - and that means you can't lift it so only a small area is immersed, otherwise sideways you go plus the float buries. No argument that curved foils plus main dagger is an excellent combination ... but we're talking about one foil doing both jobs, lift and lateral resistance - and a tight curved one is not going to work effectively, imo.
     
  11. Doug Lord
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    Doug Lord Flight Ready

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    I agree-my point was that the curved foil can be designed for any combination of vertical lift and lateral resistance. And the angle of incidence of 100% of the vertical lift can be adjusted separately from the angle of incidence of the lateral resistance. And the thing is 100% retractable. And thats it.....
    ----
    PS-my foil also works with a daggerboard but because it has a horizontal foil on it the lateral resistance portion of the curved foil is required to resist the leeward component of the main foil when it is lifting up: which is only from 4 to 15 knots when it is unloaded or begins to pull down creating a windward component to the "horizontal" foil.
    PS #2- I hadn't remembered that USA-17 used curved ama foils and no daggerboard until I accidently saw the picture in my files.
     
  12. Doug Lord
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    Doug Lord Flight Ready

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    That's where real careful design comes in because what you're saying is: use the crew to immerse the ama so the foil can work to reduce wetted surface. In other words increase the ama wetted surface so the foil can decrease it?
    My first reaction to DSS was similar to both Voyager: horizontal foil sucking air and Samnz: foil generates leeward component.
    Then I read a lot about it especially from some of the guys that are actually using such a foil and I'm mostly convinced that it is a real asset. Read the Quant 28 stuff( post #7-this thread). I do think they need to do some two boat testing to establish when it is working well and when it is not. But I think it is worthwhile to consider especially if you get help from Welbourn so you're not spinning your wheels trying to reinvent the thing.
    But nothing beats the curved foil for design flexibility, adjustability and retractability, imho.
     
  13. cavalier mk2
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    cavalier mk2 Senior Member

    It is like a T foil (or 1/2 of one) with the hull providing the column so some research could transfer. Practically speaking lack of retraction could make docking a challenge. I don't know how well the bow plates on the Crowther worked but they weren't huge to minimize the shock loads of waves before complete immersion. Some natural science research would be interesting to compare fin shape and placement.
     
  14. kiwi_bob
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    kiwi_bob Junior Member

    Yes you put it like that and it does sound silly - but that crew dance is what is already happening as I understand it - they put all the weight on the ama in an effort to get the main hull out. Trouble is, having the foil on the outside would increase RM just when you don't want that - to fly the main hull you are trying desperately to reduce it in that phase....

    so I think if you wanted to do this then having the foil on the inside of the float would be more correct - and as it's been pointed out on the outside would cause issues at docking time. You could also run a strut from the inner end up to the beam which would make it easier to build structurally and it could be lighter.... Maybe.
     

  15. Doug Lord
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    Doug Lord Flight Ready

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    Well, its all compromises and takes very careful thought. Trying to fly the main hull with the whole crew on the leeward ama sounds a bit dicy-like doing the 'wildthing' on a cat with a lot longer run!
    You can design a foil system so that you know exactly what it will do and when. The limitations you mentioned earlier about curved foils may be true on one particular boat but are definitely not true for every boat using curved foils. As USA-17 proved curved foils in the ama work well without a mainhull daggerboard. One less thing to drag. Of course, then you would need ama rudders-one more thing to drag. Compromises.......
    If you put the foil on the inboard side of the ama you take away the one really unique thing about DSS-added RM. You should seriously consider a retractable DSS type system. And getting expert help-for free.........
     
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