Power for foiler

Discussion in 'Boat Design' started by Saqa, Jun 22, 2021.

  1. Saqa
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    Saqa Senior Member

    A question of implementing inboard vs outboard. How to get that power down to the water with an outboard? I did a web search and its mostly little extension kits

    What would it take to get the outboard prop a lot lower, maybe by a metre or so?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    There was a thread where some fella did experiment with a full-foiling boat with an extended outboard leg, I recall he ran into bother with fore and aft trim when power was applied and withdrawn
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    what size boat?
    how much power?
    how fast is service speed?

    Without context, it is a meaningless discussion, which you appear to favour rather than providing facts.
     
  4. Saqa
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    Saqa Senior Member

    If it's a meaningless discussion then do not participate, quite simple really.........

    Anyway, to those that do not find it meaningless, the Yamaha F130 is attractive except for the fact prop will come out of the water at flight height by a metre or so. Has there been any precedents of running an outboard like a T foil by fitting wings to the cav plate and attaching the motor to the transom with a long jacking plate system?

    Mr E, is that how that other fellow implemented on his foiler?
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I am not sure what his set up was, but no jacking plate that I can recall, it was a few months back, how you find it, maybe try search
     
  6. Saqa
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    Saqa Senior Member

  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Looks very much like it
     
  8. kapnD
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    kapnD Senior Member

    As the shaft lengthens, the torque at the mounting point is multiplied, thus there are practical limits to shaft length.
    I’ve seen some arrangements, mostly on sailing catamarans, where the outboard is mounted to a vertically adjustable transom with several feet of adjustment available in order to entirely withdraw the motor without tilting it.
    It would have to be carefully engineered to be able to move while under way.
    Older outboards simply used 5” sections of “leg” bolted together, and the driveshaft could be lengthened by welding in a 5” section, or multiples.
    A long tail drive arrangement might work better?
     
  9. Saqa
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    Saqa Senior Member

    It does appear from everything I read that an outboard is more difficult to implement with a full foiler. The adjustable transom is what I meant by a jacking plate. There are some commercial units available, and my local plate boat builder contact is able to custom make things like that. It still means raising and lowering the whole power plant/drive train package

    Is there another way to look at this? Trying to picture a thru hull installation, the cowling can be right at the floor level and the whole leg below the hull. The problem of adjusting height still remains. How to implement that without binding issues?

    General c0nsensus appears to favour outboards over inboards, but I can't see a way to use a powerful one with foils. Longtail would be fairly easy to implement in comparison

    Thinking out of the box, one thing I will model test is a water and air pair of props. It will be interesting to see if the air prop thrust is able to take over as the foils take effect with the water prop. Will try to draw up a drive shaft to a "diff" at the transom that sends power low to a water prop and high to an air prop. There appears to be a number of sprocket and gear options to custom make something that offers the right rpm to each prop. Something like SolidWorks would be a god send!

    What do you guys think of the combined pair of props, would be a direction to explore with an inboard, or is an outboard still regarded as a better choice for a foiler?
     
  10. kapnD
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    kapnD Senior Member

    The combined prop idea has advantages at each end, but requires even more power through the transition stage, when
    both props will then be heavily loaded plus additional drive train losses.
    As with any fast water vehicle, getting over the hump range requires gobs of power.
    Perhaps a folding lattice work outboard bracket that would maintain its angle as it was lowered? (Parallelogram)
     
  11. Saqa
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    Saqa Senior Member

    Now that's an out of box idea that I can appreciate! Do you mean freely hinged, I can imagine gravity and a pod/nacelle flotation on the lower end always keeping the prop at the right height in the water? As if the nacelle is riding on suspension

    Does this make sense?
     
  12. Saqa
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    Saqa Senior Member

    Something along these lines
    [​IMG]split tran
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Are you sure you haven't plagiarized the Acme Road Runner Interceptor with that plan ?
     
  14. Saqa
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    Saqa Senior Member

    I changed the rubber band motor to an engine, that's 10% difference right there :p

    Any opinions on the "diff" and combi props?
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    Are there known analogues to this idea, a water prop and an air prop driven off the same engine ? Sounds as if it would have a lot of losses along the pathway
     
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