Hull design - CAD drawings

Discussion in 'Boat Design' started by congellous, Sep 3, 2013.

  1. Deering
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    Deering Senior Member

    The Teknicraft cats don't run entirely foil-borne. Instead, the main foil. which spans between the two hulls, a bit below WL, lifts the hulls partway up as it comes up to speed, but the hulls still remain in contact with the water. So the hulls largely control height/sinkage and trim.

    Performance benefits by reducing hull draft and surface contact area.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Only for sea trials to fine tune. Once sea trials are completed, and the optimum AoA is found, it is then fixed. So technically they are adjustable, but in reality they are fixed once set in place :p
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    As they are for all type of the HSYUCAT-thingy. But they do have a narrow niche, that being small light cats and with narrow tunnel widths. Since once the hulls become further apart the load on the foils becomes excessive.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    The forces acting on that part of the boat that is still in the water, presumably, if it is not 100% lifted by foils.
     
  5. congellous
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    congellous Junior Member

    That's what I was suggesting here. Do you think it's a workable design with the short front foil within the tunnel and the rear spanning it ? At rest I'm expecting the waterline to be half way up the cat hulls and then fully laden maybe to up to the flat
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd suggest you build a RC small model about 1 metre or so long and test your ideas out that way, you'll then get a feel for the issues involved. If there was a simple effective way to employ foils to greatly enhance performance it would have taken off like wildfire.
     
  7. congellous
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    congellous Junior Member

    Thanks, what's RC I'm guessing it's not Reinforced Concrete ? ;)

    I was wondering about a Solidworks simulation, have you heard of anyone using this method ?
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Radio controlled.
     
  9. BMcF
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    BMcF Senior Member

    At/above what speed(s) are you wanting the reduced drag benefit from the foils? I'm still not clear on that one.
     
  10. congellous
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    congellous Junior Member

    I assume there is a minimum, I've seen DIY foils on you tube that seem to become foil borne at 7 knots and above. So as low as this and then a cruising speed not much higher with as small an engine as possible 10hp ?
     
  11. BMcF
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    BMcF Senior Member

    Based on the size of the craft that you proposed but without any knowledge of the weight....I would guess that you might see some drag benefits from a pair of full-width foils at something around 18 knots and above. The power to get there would be easily 200HP....or more.

    A similarly sized foil assisted trimaran (44' LOA) that we built required about 330HP, net, to get sufficient foil lift at around 14-15 knots so that the speed could then continue to climb as the foils finally started to reduce wetted area. Once it achieved about 20 knots, the net power to maintain that speed was "only" about 280HP. Or, we could keep the throttle on full and achieve 25-26 knots.
     
  12. congellous
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    congellous Junior Member

    That puts it into perspective thanks
     
  13. tomas
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    tomas Senior Member

    I think you had mentioned this before in another thread, what was the full test weight of the trimaran? Also, what was the total surface area of the lifting foils please?
     
  14. peterAustralia
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    peterAustralia Senior Member

    A small aside, if you read the biography of the Incat owner, Robert Clifford, he says that hydrofoils dont work well above a set speed, thus if you want to go faster (like he wanted to), you go for a straight catamaran, long narrow hulls, high power, light hull. Incat boats can go 50 knots plus in lightship mode. They are up 10 112m now, next proposed vessel in a 'slow' 130m vessel at 30 knots, emphasis on lower fuel costs.
     

  15. BMcF
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    BMcF Senior Member

    Regardless of the vessel size, hydrofoils can only support a certain loading before the onset of cavitation kills their lift performance. There are hydrofoil vessels that achieved speeds in the 50+ knot range but their size and useful payload capability were far below what Bob Clifford needs to achieve to build an economically viable fast commercial vessel. One of Bob's erstwhile competitors, Northwest Bay Ships, did build a large foil-assisted trimaran to "test" the bounds of performance with foils. It was not a particularly noteable technical or commercial success.
     
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