Outboard for large catamaran?

Discussion in 'Outboards' started by Red Dwarf, Jun 10, 2012.

  1. Red Dwarf
    Joined: Jun 2012
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    Red Dwarf Senior Member

    Can a Honda 90 Hp outboard with a 14x9 3 blade prop be used for propulsion for a 60 ft catamaran(sail) weighing around 12 tons? One engine per hull so total 180 Hp.

    My concern is the prop is too small and spinning too fast so it will just be a blender in the water with no forward movement (gear ration is 2.33).

    I have seen other cats use outboards but the largest I have found is 41 ft. It is a F-41 with a very cool retraction system. It weighs 8.5 tons and uses 2, 30 Hp outboards. I can not find any reports as to how well the outboards function.

    http://www.f-boat.com/pages/news/f41Oshea.html
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Problem is keeping the props in the water, and the powerheads out of it, with the kind of pitching amplitudes involved. To mount them deep enough so they are 'biting' in rough conditions also potentially exposes the leg above the cav plate to the water flow, which will be drag inducing and create a fountain to go with it. I don't think they will be terribly efficient as motive power for the application, but they'll certainly push it along well enough if you can solve the aforesaid issues. Depends I guess on how much use you intend to make of them, they are not a solution for long distances when the wind dies.
     
  3. Red Dwarf
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    Red Dwarf Senior Member

    Look at the link I posted. The retract mechanism places the outboards far forward of the stern, so they should be able to stay in the water.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    An interesting solution, not sure why they need two engines though. Why not just one in the middle ? From what I can see, the leg is sitting quite low behind the bracket, and would drag quite a bit, but we are probably only talking 7 or 8 knots so might not matter too much. I certainly think some kind of adjustable jacking system is the way to go to optimize the depth of the prop.
     
  5. villacose
    Joined: Dec 2011
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    villacose Junior Member

    I think inboard jets in both hulls would be the way to go. if you are primarily sailing, then you don't need a huge amount of horsepower, and 90 hp per hull would be plenty.

    As much as I like outboards, i wouldn't put one on a cat or trimaran. for one thing, they just don't look right, and two, there are better options. One great thing about a cat is that you can float in shallow water. Why would you want to ruin that by putting an OB on it?
     
  6. villacose
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    villacose Junior Member

    After looking at the pictures of O'sheas cat, I have to say, that is pretty cool. A little too high-tech for my simple tastes tho. there is a lot that could go wrong with that system.
     

  7. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

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