Ama designs that create lift

Discussion in 'Multihulls' started by rapscallion, Nov 18, 2007.

  1. Doug Lord
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    Doug Lord Flight Ready

    It seems the following illustration by Guillaume Verdier regarding his 100' Gitana 17 design seems to settle the case for a planing ama on a 100' trimaran:

    Guillaume-Verdier-«On-défriche-»2---from hull design post.jpg


    Gitana 17 at the Route du Rhum start.jpg

    Gitanajaques-vabre-2017-maxi-yann riou.jpg

    GitanaTriSep2018.jpg
     
    Last edited: Mar 16, 2019
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  2. Doug Lord
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    Doug Lord Flight Ready

  3. Doug Lord
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    Doug Lord Flight Ready

    Lifting Amas: one of the first trimarans to use lifting amas was Hydroptere. Her first amas were displacement hulls but when it hit the water at speed it put the brake's on .So the new (final) ama design was a stepped planing hull that reduced drag due to ama contact with the water at speed.The shape may have also helped with takeoff in certain conditions. Each ama could carry a lot of water ballast-supplied from an intake on the rudder.

    --Displacement ama:
    Hydroptere displacement amas.jpg

    --stepped planing ama:
    Hydroptere planing ama.JPG

    -- later version stepped planing ama:
    Hydroptere stepped planing ama.jpg
    Hydroptere-in Calif..jpg
     
    Last edited: Mar 19, 2019
  4. trip the light fandango
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    trip the light fandango Senior Member

    I don't really understand the heading, Ama designs that create lift, or Dougs 100foot long beach cat or his 2stage hulls as proof except that with enough planing area , and minimising weight. a boat can plane with enough power .But canting hulls , offer some lift/freeboard at lower speeds although there is more drag due to more wetted surface area* ,and when the load/power increases the sharpness of a float/ ama/ outer hull style holds and resists leeway slide and improves directional stability when upright.They also have less flying hull/windward resistance, and would take slop and splash more kindly when lying abeam. Canting hulls need more care alongside a berth or jetty,but downwind are more likely to increase lift. My question is, why don't we see more canting on tri's and cats , say 10 to 15 degrees or greater angles? And they look better.... Having said that Petros's retractable extra planing area approach does create lift..
    *thats wrong, the shape changes but wetted surface area/buoyancy stays the same .
     
    Last edited: Mar 21, 2019
  5. trip the light fandango
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    trip the light fandango Senior Member

    I think I was a little heavy handed with my previous reply and it didn't sit that well, but it did give rise to putting a bit of thought into the subject. As Petros described a hull that adapted to planing from more of a displacement; and the concept of foiling and using dagger boards for lift has fundamental instability as part of its compromise for speed , I started thinking about an amalgam of the 2.
    What if the foil was more of a length of planing area that ran horizontal along the hull and could be folded up out of the way underneath the trampolines of a cat or trimaran. If they both had enough surface area to lift the outer hulls or just the loaded one , significant speed could be gained and wetted surface area lost without creating the integral instability that a foil creates. There are issues with forward and aft mounting arms bur presumably they would be close to immediately below the main cross beams. Anyway your original post Rapscallion deserved a more thoughtful consideration, apologies.
     
  6. tlouth7
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    tlouth7 Senior Member

    I don't see that either this or the Hydroptere example provide evidence that a lifting ama is better for a trimaran, because both of these vessels are designed to foil.

    As you say, a major reason for the lifting shape used by Hydroptere is to minimise drag in the situation where the ama touches the surface of the water (while there is still significant lift from the foil). Generally speaking a major element of hull design for foiling vessels is to create a shape that can easily break free of the surface as the foils start to do their job.

    By contrast, for a non-foil vessel all that matters is minimising drag at the design speeds. It may be possible that this is achieved by a 'planing' shape in many cases, but neither the Gitana 17 or Hydropter example supports this argument (they do not refute it either).

    Consider the logical statement that we must prove in order to demonstrate the superiority of lifting amas: at the design speed they reduce drag compared to the conventional baseline. We know that drag is composed of four elements: form, wavemaking, skin friction and lift-induced. A lifting hull will be lower drag iff the reduction in the first three is greater than the increase in lift-induced drag.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    ==========================
    I never argued that a planing ama was necessarily superior just that it was a viable solution in some cases-particularly full flying foilers. However, Jim Antrim considers a planing ama to be superior on a non-foiling trimaran.
    I disagree with this: Hydroptere set the majority of its records after switching to the stepped planing ama hulls and Gitana 17 has shown itself to be one of the fastest of the new breed of Ultim trimarans using a revolutionary foil system. The illustration by Guillaume Verdier above(post 16) shows exactly the advantages and disadvantages of a planing ama shape compared to a non-planing shape.
    I think a planing shape has great advantages on a trimaran foiler particularly my WOLF where the ama is likely to make incidental contact with the water at speed.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    Macif:
    Macif flying found 4-3-19 training for 2018 Route du Rhum.jpg

    Maserati:
    Maserati C 600 2019.jpg

    Gitana 17:
    Gitana 17 very much like FA.JPG


    ============================
    Those are just false.........Most modern foilers are fundamentally stable.
     
  9. tlouth7
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    tlouth7 Senior Member

    So you are not arguing that diagram related to a foiling boat can be said to
    ?
    My point was that the improved performance of the foiling Hydroptere cannot be used to support an argument that planing amas will improve performance on trimarans in general.

    Note that I believe the planing amas may well be better but as yet no one has presented any evidence, just a load of pictures of foiling trimarans.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    You don't think Verdier's sketches the picture of Gitana 17 planing(top picture, post 16) are evidence? How about Antrim's comment(s) and boat?
     
  11. tlouth7
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    tlouth7 Senior Member

    No, they are sketches not evidence. I cannot access any of Antrim's comments, but with regard to words or numbers available in this thread I maintain the position that (sadly) no convincing evidence has been presented to support the (perfectly plausible) planing ama concept.

    PS the image of Gitana (and all the other images) clearly shows it foiling, so how can I know whether there is any hydrodynamic lift generated by the ama shape?
    PPS even if there is hrdrodynamic lift how can I know that it is reducing overall drag?
     
  12. Doug Lord
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    Doug Lord Flight Ready

    You have the best evidence in the world staring right at you-those sketches ARE evidence because they present FACTS in a most clear cut manner from the top high performance trimaran designer in the world. Ignoring those facts seems really counter-productive! The picture I referenced shows Gitana planing on its stb ama......
    More from Guillaume Verdier:
    As is the case on the America's Cup craft, the Maxi Edmond de Rothschild[Gitana 17] is equipped with three planing hulls with inverted bows and flat bottoms, so as to increase the ability to fly and provide excellent stability in heavy seas. The central hull and floats have a high freeboard for improved protection at sea.
    ---------------------
    Antrim info post #2 and #9
     
  13. trip the light fandango
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    trip the light fandango Senior Member

    First I would like to commend you on your logic, I don't think a 100ft long beach tri is any argument for the sea keeping or crew comfort of a planing hull. You couldn't have a better example of a machine built for one specific purpose. It is always important when entering into these discussions to keep foremost in mind that it is about design speed. Unless you only refer to this aspect of a planing amas you will get nowhere with Doug and indeed find yourself foundered on the rocks. It matters not one iota that his wolf looks helpless to seaway from the stern for instance. Don't stray from design speed if entering in to a discussion with the veritable Doug. And considering this seems to have lurched into foiling ,not about the hull, it is fraught. The inherent instability of foiling doesn't seem to matter a rats arse either.I'm not even trying to be disrespectful to Doug, it's just the way it is.
     
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  14. Doug Lord
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    Doug Lord Flight Ready

    ===================
    Just out of curiosity- if you don't mind- what do the words :" his wolf looks helpless to seaway from the stern" mean? Never heard such a term before now?
     

  15. trip the light fandango
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    trip the light fandango Senior Member

    That doesn't surprise me Doug that you haven't heard it ,, I made it up, but it explains itself , your Wolf is built to reach design speed, comfort of the crew isn't an important factor..like a moths crew. a racing machine..Like mud to a formula one racing car, or a bumpy dirt track " the integral instability that a foil creates". The artists of cirque du soleil are also perfectly stable,. lifting a craft completely out of the water at speed ,supported by thin sheaves of carbon fibre looks wonderfully calm, hardly any effect from sea conditions ,pitching etc. I know your parameters , they are a sliver of boat design and innovative , I wont be drawn into a discussion on practicality, I have seen what happens, it's similar to watching the crew on a foiler when it stops dead, I have no wish to be a participant in that.
     
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