Planing Trimarans

Discussion in 'Multihulls' started by Doug Lord, Sep 30, 2006.

  1. grob
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    grob www.windknife.com

    It should be remembered that the current 24 hour solo record holder is Yves Parlier's planing multihull "Médiatis Région Aquitaine"

    Gareth
     
  2. CT 249
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    CT 249 Senior Member

    I suppose it all depends on whether we consider a boat that has so far shown itself to be slower in most conditions and faster in a fairly narrow range of angles and wind strengths is "much of a success"....
     
  3. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Isn't that what optimization is all about?
    Look at the discussions on keel/foil profiles for example.
    Or athletes, the "10-fighters" (don't know what you call it) doesn't win a 100 meter run or the 10.000 meter.
     
  4. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Oops, I forgot I was out of this :)
     
  5. grob
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    grob www.windknife.com

    I don't think many people would agree with this point of view, (Please jump to CT249's defence if you think I am wrong). I think that a boat that is capable of holding the current 24 hr distance/speed record on the ocean should be classed as a success. Sure there are other boats that will beat it in other conditions, but that can be said of any boat ever built.

    It is probaly still at the begining of the learning curve with regards to biplane rigs and planing hulls, and may go on to do better things, maybe not. But I personally consider it a success in proving that both these concepts may have a future.

    Gareth
     
  6. CT 249
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    CT 249 Senior Member

    Yeah, you may be right from some angles. I was under the impression that the cat was about the only boat specifically going for the record, as distinct from going for it in the middle of another event; I may be wrong. Biplane rigs, planing hull cats and stepped hulls in sailboats have been certainly been tried many times before, of course.

    I suppose many people have very different definitions of "much of a success", compared to "a dog", "a success", "just another boat", "a downhill flyer", a "great allrounder" or whatever other ways we can describe a boat. If the ability to be good at one thing makes a raceboat "a success" then about 99% of them are successes, I s'pose, because just about every boat has some strong point.

    From the perspective of a racing sailor I can think of many boats that were quick in some winds but not generally considered to be a success. Just to pick a class at random, in IOR 30.5 One Tons Roperunner, Espace de Desire, Jockey Club, Wildcat (?), Rubber Duck, Local Hero, Sidewinder, Constance, the MAC 1s and many more were written and spoken about as being unsuccessful although all of them were very competitive (among much bigger fleets in a vastly bigger class than Mediatis) in one or two sets of conditions. Many boats can excel in certain conditions...whether than makes them a "much of a success", or a one-way wonder probably depends on your point of view. I know a few boats that were the fastest thing in their country in certain conditions but were generally regarded as dogs when seen as an all-round raceboat.
     
  7. Baronvonrort
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    Baronvonrort Junior Member

    The current record is held by the 60ft trimaran Brossard at 610nm.
     
  8. grob
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    grob www.windknife.com

    I stand corrected. Thanks.

    Gareth
     
  9. Doug Lord

    Doug Lord Guest

    Moth hulls and planing/ Ilett, Wardi,Culnane,Smith/voodoo

    ----------------
    Regarding the Moth in sehugging mode: According to John Ilett, Moth Designer:

    Saved e-mail message
    Prowler
    "I believe that technically they are planning hulls even though some say they are like a displacement cat hull. There is just a less obvious hump to get over and onto the plane and this is exactly what makes the boats so quick in light to moderate conditions where other boats are very draggy just trying to climb that same design hump.
    John Ilett"
    ----------------
    According to Doug Culnane, Moth Designer/Researcher:
    "Hydrodynamic lift is likely to be as large in magnitude as the buoyancy in ths speed range[11.1knots and above]Most craft are said to start planing at a Froude number of .8[Most others say at a Froude number of .6 or a speed/length ratio of 2/ For a seahugger Moth Fn.8= 8.82 knots;Fn.6=6.63knots ]
    However, due to the slenderness of modern narrow Moth designs they will not plane until higher speeds are attained. At a Froude number of 1.5[speed/length ratio of 5-16.5 knotsfor a Moth] it is safe to say that the craft has the potential to plane. A transom will run dry, and a trim angle of two or three degrees is realistic.Correctly placed chines will reduce wetted area by expelling green water into a spray sheet."
    ----------------------------
    Another famous Moth designer, Ian Ward, says:

    Saved e-mail message
    Subject: Re: Moth
    Doug,
    This is a difficult one!
    It depends on your definition of planing. If exceeding V/sqrtL=1.3 is planing, then these things plane in almost all conditions ie: at hull speed over 4kts or so.
    If you mean lifting out of the water, well they glide fast up to about 8kts like a cat, but after that, lift and slap about on the surface, planing from about 8 to 10 kts hull speed.
    regds, Ian

    ------------------------
    Two messages from Alan Smith, designer and researcher:
    Saved e-mail message
    #1
    Doug
    Let me stress these are nominal numbers and as I tried to indicated "planing" is largely perception
    205 lbs 300mm beam
    At 8, 12, 16, 20, 24 knots the dynamic lift to AUW ratios are .17, .37, .60, .80, and .92 respectively.
    My guess is that most moth sailors would claim to be planing at 12 knots and all would be positive at 16 knots.
    Alan

    #2
    Saved e-mail message
    (note divide Fn by .3 to get speed/length ratio/dl)
    Doug
    I have run some nominal numbers
    But we must first decide "What is planing?" It is not simply going faster than a Froude number of 0.4. Pilot boats and life boats such as used by the British Sea rescue service achieve Froude no. in excess of 1 by shear horsepower.
    The Australian 18 foot skiff at 600 lb 4ft chine beam hits a Froude number of 0.4 at 6 knots but at 14 knots 10% of its weight is still supported by buoyancy. That puts the small stern wave about 16 feet astern. To get a 190lb moth with a chine beam of 16 inches to the same point a speed near to 20 knots is required.
    My understanding of the size of the hump is that it is driven primarily by the AUW to length ratio. Hull shape is also important. Thirty years ago I had a 14 ft skiff (now international 14's); 42 inch chine beam, that did not exhibit a noticeable drag hump, trimmed bow down up to about 5 knots and then trim aft an she would lift out and plane easily. Magic!
    Regards
    alan
    ++++++++++++++++++++++++++++++++++++++++++++++++
    I've been trying to get to the central problem here and it seems to me that it is not whether or not narrow hulls will plane-they will at the right speed and with the right hull geometry. And it's not the fact that high beam to length hulls can exceed hull speed say up to 4-6 times the square root of the waterline-we know that happens. It is, probably, the failure to explain well enough that at a given angle of heel if the main hull of a tri is still supporting weight then depending on the factors involved-speed, beam to length ratio, waterplane area and hull geometry it could plane. The fact that the designer and owner/sailors of the F-boats claim that those boats plane on the main hull doesn't appear to matter; the fact that the science shows that an F22 has the power to plane upwind with the ama partially loaded is not understood/accepted. The fact that Jim Antrim says the ama's on his 30 footer are "planing ama's" is discounted.
    So if all this evidence is discounted-the designer, the sailors, and the science-what other factors could be introduced to convince the "non believers"? Video won't do it-you need to know the science behind the design and the factors affecting it at that moment. And the science is discounted....
    Is it a matter of faith? It must be to some since facts and science are discounted.
    I think under these terms(science not reliable, designer not reliable, sailors not reliable) there can be no answer except, well, voodoo.
     
    Last edited by a moderator: Oct 9, 2006
  10. Chris Ostlind

    Chris Ostlind Previous Member

    Ahh, yes, the shrunken skull approach

    And in this statement, you have hit the nail on the head. So far, and this is to be confined to a trimaran... the claims are, indeed, VooDoo.

    And just to keep it clear and accurate, Antrim never has claimed that his amas plane. He only states that they have planing shapes. When you get that, you'll understand a whole lot more of the argument beyond your narrow, "I'd like it to be this way" viewpoint.

    Sometimes, Doug, you have to put aside your worship of "all things performance oriented" in order to get the bigger picture. A fast boat like a trimaran does not need to be included in the heretofore claims of being a planing vessel in order to get it on and kick butt. Why you insist on having trimarans included in that environment is more than a little off track, as far as I'm concerned. And that position is held by more than a few of your fellow list members as well.

    So, the reality of this continuing charade is that you refuse because you have to have it that way while everyone else gets it. Does that reality not simply knock you back on your seat and cause you to engage a series of deep reflections on all these claims of yours? If it doesn't... it really should. And that, my friend, is where the real VooDoo is at work in this quest for a planing F-Boat. Not that you originally suggested that the planing tri in question was the F22 and not one single example of this design is currently even on the water to gather that proof. You're running purely on speculation and the marketing claims of Farrier. Please, Doug, at least wait until the boat is sailing to stick your cheese in the wind without any real world support for the claim.

    A twin engined Cessna is not going to break the sound barrier, a Honda 600 is not going to set an all-time lap record at Daytona, a cigarette boat is not going to set an unlimited, world speed record for boats.

    All of these are fast vehicles in their own right, yet they have design limitations that prevent them from getting to that place of ultimate claims. The F-Boats fall under the same, Not Gonna Get There, design limitations as all the other nice products on this list unless they can produce irrefutable proof to the contrary.

    I'm quite sure that if you can produce this phenomenon with any F-Boat, anywhere in the world and there is a collection of video proofs to support such claims, that the science will already be there.

    Take some time off and think it through. You'll be a lot more peaceful in the end.
     
  11. Dan S
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    Dan S Junior Member

    Some beneficial reading:
    http://en.wikipedia.org/wiki/Occam's_razor
     
  12. CT 249
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    CT 249 Senior Member

    Interesting stuff. As I said, there are designers and sailors on each side of the Moth question. I don't even think it's important which view is correct (just my opinion); nor do I think it's impossible for a tri to plane and I think Farrier tries to get them to plane.

    I was merely trying to point out that it remains debatable whether a Moth planes and it's therefore hard to use Moths as ammunition for this debate. In context of this debate, the fact that there remains some dispute is surely relevant. If the people who design and sail Moths can't all agree whether they plane, how can we who don't design or sail Farriers work it out?

    Secondly, as Alan's and Doug C's replies indicate with their reference to the narrowness of Moth (and tri) hulls, they plane later in the speed range. Therefore, as Torr had mentioned and basic planing theory underlines, a simple power/weight or weight/wsa isn't enough to work out what planes. A narrow hull like a Moth or tri will not plane at speeds where a wide hull with identical weight and SA will plane. This is well known and it shows the weakness in early calculations here.

    Dave says a narrow Moth will plane at around 16.5 knots. I think Alan's saying that at a beam of 16 inches a speed near to 20 knots is required; however the modern narrow boats have a beam of 12 inches. I think guys like Emmett say that a seahugger's top speed is 17 -19 knots; so it's rarely planing if you take Dave's 16.5 knots or Alan's 20 knots. Obvioiusly, we have to throw Wardie and John, with their excellent qualifications, into the "planing" camp.

    With Andy, Stevo, Thorpie (from memory) Andy Dovell and Emmett (from memory) on one side and John, Wardie and Doug C. on the other I think it's fair to say it's not clear cut, as Wardie, Doug C. and Alan say. The fact that these sort of questions remain open surely means that we can't all be so adamant about them. Non-believers and believers can both be reasonable.

    EDIT: Sorry about getting D Culnane's name wrongh; too many Dougs.
     
  13. ActionPotential
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    ActionPotential Junior Member

    Agreed, and my point is that the only time we can declare the centre hull of a trimaran is planing is when the heeling force is not shifting the c of g, that is when it rises with both amas out of the water. And I am confident that this can happen. I concede that a trimaran can have a planing centre hull and that it can plane on it. Its just that we haven't seen it because all that we have seen are trimarans with their centre hulls lifted by heeling force.
    I also concede that we can have planing trimarans that can plane on their amas.
    Finally do we count foil borne as planing?
    I do and thus we have examples of planing trimarans.

    The trimarans with fat centre hulls have the advantage that as the centre hull is lifted by heeling force the wetted surface is dramatically reduced.
     
  14. Doug Lord

    Doug Lord Guest

    planing

    Foilborne boats are definitely not planing since they are dependent on lift from both sides of the foil.
    At least most of the time:
    Manuel_sard.jpg
    Address:http://www.moth.it/Manuel_sard.jpg Changed:1:29 PM on Monday, October 9, 2006
    ------------------
    CT, it's Doug Culnane, not Dave.
     
    Last edited by a moderator: Oct 10, 2006

  15. ActionPotential
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    ActionPotential Junior Member

    The only foilborne boats I have actually seen are (were) the Sydney Harbour Hydrofoil Ferries. They didn't look like they had lift from both sides of the foil.
    Seems to me a trimaran will be fastest sailing on one ama, regardless of the shape of the centre hull.
    I have no doubt that the farrier 'planing' centre hulls can plane, under motor, or downwind with both amas clear of the water.
     
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