Offshore Foiling Revolution-Gitana

Discussion in 'Multihulls' started by Doug Lord, Apr 16, 2015.

  1. Corley
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    Corley epoxy coated

    It's not really a huge leap for a MOD70 they already were foil assist and a MOD70 weighs less than an AC72. Way back in the ORMA60 days the rules were tweaked to prevent fully flying boats so the ideas have been in gestation for a long time. It will be interesting to see how they tweak up the foils for offshore use the team press release noted that the peak speed wasn't as high as they would like so obviously some work to do there.

    http://www.gitana-team.com/en/event.news.aspx?eventid=97&newsid=1123
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Gitana Foiling

    Corley, are you sure about the weight of a MOD 70 and AC72? That tends to put to rest the old argument that "a cat is always lighter than a tri".....
     
  3. Corley
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    Corley epoxy coated

    Good point Doug I've read that the AC72 was heavier than the MOD70 in sailing trim but looking into it further at the minimum weight for an AC72 it was listed as 5,900kgs lightship now I'm not sure if the AC72's were able to be built down to that weight or not. The MOD70 is listed as 6300kgs light ship on the MOD70 website in original spec.

    It would be easy to get a MOD70 down to that weight though. For starters they have a quite heavy engine in standard spec. If I recall correctly that was due to a requirement to meet a minimum motoring speed for transiting the Panama Canal unassisted. The Gitana team have already made a number of changes to take weight out of the platform including ripping the old engine out and replacing it with a lighter unit so I wouldn't imagine the weight difference would be very great. 400 kgs on a 6 tonne odd boat is only a relatively small difference and MOD70's were not built as light as they could be due to the one design requirement.
     
  4. Jim Caldwell
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    Jim Caldwell Senior Member

    Foilers need a much stronger structure than a displacement boat because of the much higher loads required to keep the stiffness or flex will change the foil angles.
    If you add in foil RM, more stiffness is required.
    So yes, you add some weight, but you add a lot more speed also.
     
  5. Corley
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    Corley epoxy coated

    The foiling that Gitana is displaying looks just right to me. Offshore I don't believe you would want to fly too high because you want the benefit of the trim corrections that the long hulls give you when they gently immerse. Look at the violent crashes that AC72's had when they came off their foils you couldn't survive those sort of incidents offshore without breaking the boat.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    Gitana Foiling

    I think they look damn good, but I'm convinced that any tri that wants to foil-especially in the ocean-would do better with a vertical lifting foil on the daggerboard.

    PS-Corley, how much wind do think they are sailing(foiling) in?
     
  7. Corley
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    Corley epoxy coated

    It's always hard to judge from videos but judging by the seastate it could be about 5 beaufort or so somewhere in the range of 20-25 knots.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    Gitana Foiling

    Thanks-I was thinking 15-20 but it's real hard to judge.
     
  9. rapscallion
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    rapscallion Senior Member


    I wonder if such an arrangement would require a great deal of structural modification to a MOD 70 when compared to adding a foil to the Ama, as the daggerboards on Mod 70s are swept vs. vertical. Money is no object with these guys, but once you have to put a certain amount of work into an existing boat, you midas well start from scratch with a new design, which is what several people seem to be doing elsewhere.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Mod 70

    If you've followed Wild Oats XI at all you know she is undergoing another major set of mods-cutting the stern off then cutting just ahead of the mast to extend the bow etc. The point is that they've done this repeatedly and the boat is still super fast so I think any mods to a Mod 70 could probably be accomplished w/o negatively affecting speed/performance.
    But the hard part, in my opinion, would be getting the design choices right.

    PS-I'm not suggesting adding a foil to the daggerboard instead of an uptip foil in each ama but in addition to. I'd also suggest adding a single rudder t-foil to the main hull rudder and no rudder t-foils on each ama. The angled daggerboard is not ideal for mounting a lifting foil, so that and the structural implications would have to be carefully studied. Whether or not to use a surface piercing T-foil instead of a wand(or an electronic altitude control system) is another major problem.
     
  11. rapscallion
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    rapscallion Senior Member

    Is there a reason why the lifting foils on the center hull couldn't be like the ones found on the quant 23 scow? That way, the center foils could be fully retracted in seahugger mode and could be cleared of weeds more easily while under way.
     
  12. Doug Lord
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    Doug Lord Flight Ready

    Foils

    Weight and complication if downforce was desired. I don't think concern for weeds is a high priority on those boats(Gitana and Macif): they have an uptip foil and a rudder T foil on each ama. I'd be interested to hear from experienced people that have sailed long distances on big tri's about weeds on "C" ama foils or rudder foils.
    The Q23 foils are fantastic but probably would be hard to implement on the main hull of a tri.
     
  13. rapscallion
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    rapscallion Senior Member

    Good point about weeds and an ocean tri. I was thinking more of applying the tech to a 25' to 30' racing tri. I noticed that hugh mentioned adding racks to the Q23 on the SA forum so the foils wouldn't stick out past the boat's footprint, and I thought maybe placing such foils on a trimaran's center hull might be an easier way to get a tri to foil and still allow for the foiling foils to fully retract in light air and to clear weeds.

    So far, the trimaran I'm most impressed with in terms of foiling in big waves is the catri. Granted, the older designs were only foil assist, but it probably wouldn't be too difficult to get the boat to completely foil close to the water surface. It's too bad the sea stays are set up the way they are on that boat. They made for an insanely wet ride.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Have you seen the "C-Fly"? It's foil system is designed for rough water.
    The Fire Arrow system is excellent for rough water since the main hull is always clear and the main foils are deep. And the flying angle of heel is adjustable.

    C-Fly:

    click-
     

    Attached Files:


  15. Doug Lord
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    Doug Lord Flight Ready

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