why has high buoyancy become so important?

Discussion in 'Multihulls' started by peterchech, May 6, 2011.

  1. Ilan Voyager
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    Ilan Voyager Senior Member

    Yes I'm mixed with the Fuji and derivate names, I'm talking about the one skipped by Mike Birch, which male form was made in 1986-87 at St Philibert, near La Trinité (Brittany France) in the Charlie Capelle's shop. Nigel Irens was in the same time sculpting the piece of wood that became the model of Ilan Voyager...I was there, so you know now the origin of my pseudo...

    Several sisterships were made from the molds, like the ill fated Laiteries Mont St Michel. It was radical compared to the precedent generation, but compared to the actual multis rather "bland". A big difference also in the material. They were using kevlar. Ollier pioneered the all carbon fiber and he was right, kevlar has too many drawbacks.

    Gary, for me when you can sleep inside out of the rain and heat a can of raviolis a boat like the Seacart is a cruising one as you can spend several days on the boat. Ok, the amenities are spartan but enough to have a good week of fun of fast coastal cruising...

    I knew very well the Charles Heidsieck. Apart the weight, largely underestimated by the designer, it had many other faults as for example the assumption that the wings will give portance.
    The problem of monohull designers adventuring in multihulls is to believe that their experience of monos will be useful. Nope, multis are very different beasts. Finot-Conq and Harlé made also the hard experience: their Formulas 40 were never competitive.

    I'm surprised that none has made comments on the Paradox hulls. The movie shows them at different angles and there are obvious features.

    The Hydroptere of the world records is not old school...the design of the foils is top, and ballast are used to give the best angle to the foils, but remember that more than 16 million bucks have been poured in this long time project and the boat has never made an oceanic race (and it's not competitive for that). Mean time dozens of tris were made and racing at a fraction of the cost...
    "True" Foilers are beautiful and interesting, but the main problem for racing is in the foils...almost impossible to get a good behavior, unless complex systems like controled ventilation and variable camber of the profile, over a large range of speeds and sea states. Even the military broke their teeth on the foil problem. With "fixed shape" foils it's like trying to fly a 747 without the high portance system at low speed or try to go fast with all the flaps out... Another problem with the small ama foilers is the mast...where to put the rigging hardware?

    The Russian foiler ferries work very well on a limited range of speeds under 35 knots, and the same Russian engineers will tell you that going over 40 knots is problematic.
    There is a kind of "wall" at 35-40 knots where cavitation obliges to design profiles that will work over 40 knots but are almost useless under 35...It's a bit like the hump of the planing boats.

    On big ama trimarans assisted by foils the problem is different; foils are used only when the speed (ie Reynolds number) is enough high, so the design of the profile is simplified as the range of speeds is limited. And there are plenty of cross arms to put the rigging...and keep the mast straight and vertical.

    An example of good cruising tri Nootka http://www.nootka.fr/Nootka/Claude_Develay.html. In French but plenty of pics.
     
  2. Doug Lord
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    Doug Lord Flight Ready

    buoyancy

    ===================
    I guess it's not really the ocean but Hydroptere did set a record across the channel. Team Hydroptere seems to think that a full flying foiler can be competitive across oceans-in fact that's what the whole project is about. I read that they were going to try some sort of record in the Pacific fairly soon.
    Also read a story that they feel(as do I) that the biggest hurdle any ocean going foiler faces is crap in the water so they were working on a unique system that would spot objects just above or below the surface in time for them to avoid a collision. In my opinion, a system like that is absolutely essential for an ocean going foiler.
    Hydroptere.ch has been launched to serve as an experimental test bed along with the original boat to lay the groundwork for a 100' Hydroptere maxi that they hope to use to break the round the world record. Hydroptere.ch uses two retractable surface piercing foils in combination with two retractable rudder t-foils. In addition they are experimenting with a variable geometry solution to a stepped planing hull. Interesting stuff and a lot more to come from Team Hydroptere.
    --
    On small boats, foils have proved to be extraordinarily fast with the Moth the fastest sailboat under 20'-beating all cats and the aussie 18. Foils on kiteboards just recently won a major regatta against planing boards and a new French foiling windsurfer holds a lot of promise.
    --
    I think both full flying and foil assist have tremendous potential in designs from multihulls of all sizes to dinghies to monohull keelboats- with V3 winning the BWR using curved lifting foils. Lots to look forward to!
     
  3. Ilan Voyager
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    Ilan Voyager Senior Member

    Doug, crossing the Channel is not all weather oceanic racing...it's just seeing the salt water and smelling the breeze. They are far from having a competitive ocean racer...But I hope to see the big one.

    I do not mean that foils are inefficient (there too many proofs of the contrary on dinghies) but on oceanic sailing the requisites are different. And for the while there are a lot of problems to solve.
    The curved foils are the illustration of what I wrote of the full big amas tris. Used only when needed and in their range of speed.
     
  4. Gary Baigent
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    Gary Baigent Senior Member

    Ilan V, foils have been on ocean crossing multihulls going back to Dave Keiper's ladder foil Williwaw, back in the 1960's - okay didn't make fast crossings but he was the first to do it. I watched Williwaw going fast one regatta day here in Auckland, (he'd come from Hawaii) going a lot faster than we were on Drumbeat (hey, Cav).
    Tabarly's Paul Ricard was also outstanding - first round Bermuda in the 1979 Transat en Double; it was mostly a beat to arrive there, and second by a few minutes on the return to Lorient by the Kelsall VSD - VSD also had foils set in the main hull (although they got damaged and were removed in Bermuda). Paul Ricard was alloy and also overweight, a later, lighter version, new beam, lighter rig, was the first to break the long standing Atlantic crossing 12 day record held by big 3 mast Atlantic, Tabarly did it 10 days - that was a breakthrough milestone.
    As you say, crossing the channel by Hydroptere is no ocean but the record is still impressive, faster than Bleriot's early aircraft crossing, not bad for a yacht. Also they were well out in the Atlantic during another record attempt when they hit something and damaged the boat. That is a problem not only suffered by foil designs, but all modern yachts, even monohulls like the 60's and 70's because of their bristling appendages.
    You're talking about the second generation ORMA 60's, after Paragon and Apricot, the third bunch are those with long floats and foils, square platforms and wing masts like Fujicolor, Groupama 2 (really the 4th and last generation) and company.
     
  5. cavalier mk2
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    cavalier mk2 Senior Member

    Gary I'd put foils on my Vagabond but every now and then we wind it up and it goes plenty fast for me.....I remember seeing photos of Williwaw, didn't J.S. Taylor pioneer some foils to ?
    So what do you think, angle foils in the ama just behind the main beam or full bananas ?
     
  6. Doug Lord
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    Doug Lord Flight Ready

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    Curved foils are far more adjustable than angled straight foils or t-foils w/o altitude control. You can adjust:
    1) angle of incidence of only the lifting portion of the foil-not changing the lateral resistance portion of the foil at all,
    2) the lift profile of the foil by small deployment/retraction and or by canting the whole foil(Aethon),
    3) you can design a trunk that will take more than one radius of curvature and design the radius to allow more or less vertical lift.
    4) you can design the trunk to be at a fixed toe-in or have toe-in adjustable completely independently of vertical lift.
    5) curved foils are more efficient than fixed t-foils because they never have high and low pressure on the same side(leeward foil deployed only)
    6) straight angled foils always have the same % of lift vs lateral resistance unless their athwartship cant angle is adjustable-this can be adjusted on a curved foil by simply moving the foil up or down.
     
  7. cavalier mk2
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    cavalier mk2 Senior Member

    Thanks Doug,there is some thing to play around with.....hard to justify for a cruiser though.
     
  8. Ilan Voyager
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    Ilan Voyager Senior Member

    Doug and Gary, I'm not despising foils, as I have already said it's a very interesting configuration. Yes, some foilers has been successful (I do maintain that the first version of the Paul Ricard was a pain...) years before, when the speed of the records were roughly one half of the speeds today.

    I'm talking about competitive OCEAN racing machines today, now in 2011. There is not a competitive "true" foiler nowadays in the racing circuit.
    By "true" foiler I mean a machine able to take out of the water and fly like a moth or the Hydroptere.
    The other in this very moment are trimarans assisted by foils and do not intend to get out of the water, thus these tris are not true foilers. The foils are used for "help" the amas and also on the rudder to stabilize longitudinally the boat, but basically these tris are displacement boats not flying boats. I've ended with the semantics.

    I can say that Irens is working very hard on true foilers with his associate Cabanel...

    There are several explanations of the absence in the racing circuit of "true" foilers.

    In my opinion the main one, is that I have already told in the post #46 is that it's almost impossible to design a foil working with a good ratio Cz/Cx in all the range of speeds from let's say 12 to 50 knots for ocean racing, unless going to complex devices.

    Moths are very light so the charge per square meter of foil is low and the Reynold numbers is pretty small with plenty of power to move the machine. So the foil drag is not too problematic. It's a situation similar to some radiocommand competition gliders.
    The Hydroptere is very fast in specific conditions, but nobody has seen this boat in competition on a triangle regatta or oceanic race. So none of us knows really how
    competitive is this boat. I suspect that it won't be very good because if it was a good all around all weather boat it will be racing...not in development (more than 20 years now...)

    If oceanic (or high sea) foilers were easy to design and make all the major navies would be using them as at least as patrol boats. Boeing made civil and military foilers and none remained in service. Very complex and very expensive to maintain. The high sea over 40 knots ferries are gone to the cats (assisted by foils sometimes), and a few tris, not the foilers.

    There is a limitation anywhere...isn't it? The range of speeds, the reliability and potential fragility and last but not the least complexity.

    That shows that the design problem for an oceanic racer is a very hard one...Design the good foil, design enough simple devices to suit the foil to the different speeds and sea states, and design a longitudinal stabilization system to keep the foil in the optimal range ( a negative angle of attack is a frightening situation...) at an "affordable" price, rather simple to use without 3 computers and 2 PhDs on board and reliable enough to cross an ocean.

    I do truly hope to see a competitive "true" foiler for racing... Probably the next step is a trimaran with almost full amas with foldable foils able to fly while being in the optimal conditions...so 2 days of flying in a 10 days race and the race is yours... A hard to design hybrid...air drag will be the main problem at high speed.

    (That do not condemn foils; the moths are fascinating, the small russian ferries rather efficient, and with some improvements excellent cruising foilers can be designed - Michel Fortin designed long time ago good ones-)

    Cavalier, a cruising "semi" foiler is less expensive to make than a trimaran with big amas, with the same amenities. If the boat stays in speeds under 20-25 max speed (that's evident...) the design of the foils is rather simple. I would see it for costal cruisers. The drawback is that the fashion (and imitation of the racers) is on the side of tris.
     
  9. Gary Baigent
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    Gary Baigent Senior Member

    You've got a good, fast enough cruising boat, Cav, and what Doug is suggesting is foil complexity and sophistication that isn't necessary on your Vagabond. Just IMO of course.
    Yes, I remember seeing some of J.S.Taylor's dense illustrations on foiler and proa designs ... but did he ever build one?
     
  10. cavalier mk2
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    cavalier mk2 Senior Member

    I think he did Gary, I'll have to dig through my archives.....Yes I know the boat is a fast enough cruiser, we haven't buried the amas yet (not completely any way! ) and the slender shape helps cushion the shock loads in gusty conditions like early spring around here. I think Voyagers suggestion on external foils is the sensible course for cruisers to avoid blowing out the amas on debris-kick up etc...
     
  11. Doug Lord
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    Doug Lord Flight Ready

    ===================
    Ilan, I think you have made well reasoned comments about full flying foilers as ocean racers-I don't blame you for being skeptical. I hold a different view in regards to the potential success of the Hydroptere team in their major goal: the round the world record-I think they'll make it.
    I think any very fast small boat in the ocean today needs some sort of electronic assistance to avoid dangerous objects at or just below the surface. That, in my opinion, is the single greatest impediment to full flying ocean racing foilers.
    I think the use of "foil assist" where the foils lift up to 60-70% of the weight of the boats has been well proven on ocean racing multies and now is beginning to be proven on ocean racing keelboats-lots of pioneering work has been done and continues and lots of room for development in the application of "foil assist" to multies and monos.
    Back to the buoyancy subject of the thread for a second: most "foil assist" trimarans and catamarans don't use rudder t-foils(yet) and therefore rely on buoyancy of the hull for pitch stability when flying the main hull of a tri or second hull of a cat. I think that is a major factor in all the new designs that use foil assist. If they did use rudder t-foils then the ama could be smaller.
    I think this is similar in conception to Hydroptere.ch where it uses retractable main surface piercing foils and rudder t-foils as well as variable geometry hulls that allow the boat to use stepped planing hulls.
    ----
    Again, Ilan, your comments and insights are most welcome-while we may have different assessments of the future I think we agree on the present....
     
  12. Doug Lord
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    Doug Lord Flight Ready

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    Cav, I'm not suggesting lifting foils for a cruiser-I wouldn't do it. My suggestions were based on my impression that you had decided to do it and ,given that, what would be the simplest installation.
    I disagree with Gary that what I suggested was "complicated" only because I was talking about adjustability not a series of operating controls. I learned about this the hard way on my own boat. Common sense told me I should have everything adjustable but I got in a hurry and fixed the angle of incidence of the main foil. That was a big mistake that cost a lot of time.
    If you're going to use a lifting foil then it MUST be adjustable at the beginning. After you sail with it the settings can be more or less permanent-no constant adjustment is required. All you need to do is be able to slide the board up and down. Manual adjustment of the angle of incidence is simple, not complicated and a good thing to design into any curved foil installation-for crying out loud the Nacra 20 and DNA A Class cats have this adjustment facility.
    For the inexperienced builder(tooling builder) curved foils may seem more complicated than straight, angled foils. Maybe a little but if you study how its done -not too bad. Curved foils, however offer much more in user friendliness than do straight angled foils.
    At any rate, I'm not suggesting that any cruiser use foils though there are benefits in improved handling in some cases.
    ---
    And, from what I can tell, the more buoyancy the better on most cruising designs......
     
  13. cavalier mk2
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    cavalier mk2 Senior Member

    We have plenty of buoyancy, pushed the boat hard when light and heavy to make sure. I was being a bit tongue in cheek about hotrodding vintage tris. Alan Nicol wanted to make a light foam composite one ! I agree about adjustability to dial things in. Cruising does put a lot of demands on your time and foils don't seem set and forget ! I agree about collision detection, prevention is always better than cure. Gary's comment on williwaw got me thinking about the 1st Newick Echos which had dynamic lift "new moon amas" as well as angled ama foils. I called him after they'd been out a few years and he said the amas didn't need anywhere near the curve drawn and had been redesigned.
    Gary you've sailed Newicks with those foils, how much did they help?
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    Max Purnell's Mokihi was always a good boat, but with the angled foils the boat was better, especially in a seaway when the pitching motion was reduced. Also I remember times without foils, when overpowered in high winds, we'd bury the leeward ama so far that the immersed, disappeared, bow section would be throwing a vertical bow wave up and back, erupting from the surface, like Excalibur's sword. With foils this didn't happen, ama stayed visible - which is better for speed ... also nerves.
    So contrary to what Doug says, if you're determined to put foils into your Nicol, then I'd do what Mokihi had: simple, angled, asymmetric foils set at a couple of degrees attack. They can be lifted or lowered to positions suitable for wind strengths, but mostly you'll find there is a good average position and will leave them there. In light winds, beating, have the main hull dagger right down and the leeward foil also - Mokihi cleaned up all the Auckland competition in those days when set up like this.
     

  15. Samnz
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    Samnz Senior Member

    http://www.hydroptere.com/index.php?page=l-hydroptere-maxi-en---presentation

    looks like the Hydroptere team have ditched the low buoyancy floats.

    I guess they have good reason to believe that high buoyancy floats are better?

    Why do you think that is Gary?
     
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