reshape hull to fit triple engine setup

Discussion in 'Boat Design' started by captbali, Mar 25, 2014.

  1. captbali
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    captbali Junior Member

    Hi guys,
    Any advice and opinions would be appreciated here.

    I have found a 38ft intrepid stepped hull, it was originally designed to run with twin 275's but the previous owner installed triple 200's. With the stepped hull the outside engines are sitting outside and low of the hull line and causing a lot of drag. The boat reaches 35 kts with everything in her favour but against current and swell the stern bogs in and can slow to 15 kts in the worst case, chewing feul.

    Repowering with twin engines is not financially possible for me, but 'boxing in' the back step before the transom is. I could extend the original v from a metre ahead of the transom where the step starts and slightly flatten out the v (taking out the step and turning it into a normal hull) and add a few more inches to the depth of the hull at the transom which would effectively have the engines sitting at a much better height. (Cav plates on outside engines currently submerged around 15 cm from water line when on plane)



    Any ideas please
    Thanks
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Sounds like the transom height is not right for the shaft length of your engines, or the outside ones anyway. Would jacking plates help ?
     
  3. captbali
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    captbali Junior Member

    Yeah the transom height was fine for twin engine setup. Now with triple the centre engine is at the right height but the sides aren't. I looked at jackplates but using them on the outside engines and not the centre will probably cause problems with the hydraulic steering rams as the centre engine is attatched to the outsides. Pushing them out and up with the jackplates might interfere with the steering?
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    So all the engines are the same shaft length, what, 30" ?
     
  5. captbali
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    captbali Junior Member

    I think 20? But yes they are all the same
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Maybe 25", but doesn't matter, you are stuck with them. Can't say you see many boats with engines at different heights, so maybe the steering linkages are difficult to manage, but it may be doable. Best to get someone local advice on that, may require modifications and adjustments to get right. That still leaves the engines needing to be raised, you may be able to get something fabricated to raise the transom height for those two engines. I think I'd prefer that route to padding out the bottom of the pod. You will pay $ which ever way you go. But as it is, isn't any good, if the legs are dragging like you say.
     
  7. captbali
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    captbali Junior Member

    Thanks for the input, will be raising the outside engines up to the highest boat hole on the weekend. I have hydrofoils on each engine, but so far under the surface I guess they are just adding to drag.... will try with the outsides off. Building the transom higher and reinstalling the outside engines a bit higher was something iblooked at, but it seems just as big a job as filling in the pod.
    Thanks for input Mr Efficiency
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Can you move the outer engines in at all, closer to the central engine ? Incidentally, I think those hydrofoils would not be any use for this problem.
     
  9. captbali
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    captbali Junior Member

    No they are close together as is, I will look into the fixed jackplates. Each engine can tilt free of the others so hopefully the steering linkages wouldnt take too much adjusting
     
  10. raffshore
    Joined: Nov 2008
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    raffshore Junior Member

    We did a lot off tripple installations even on smaller boats. (tripple yamaha's on 28 ft phantom, not stepped)
    The hydrofoils won't do anything

    How far are the engine appart and what height?
    What set back?
    What engines? Low water pick ups?
    You have some pics from the back of the boat like they are mounted now?

    You should have around 10inches off set back (if you have non under the hull)
    Maximum 1 inch between the engine covers
    Around 2.5 inches (each) under the V (hydraulic jack plates is the best, you lower to plane and bring them up for top speed)
    We always used 2 20 inches and 1 25 inch in the middle (20LH 25RH 20RH)
    Then some good 4 blade props and you should be around 55 to 60 MPH

    The extra engine won't get you more speed, only more acceleration
     
  11. captbali
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    captbali Junior Member

    I'll have some photos and measurements after the weekend
     
  12. raffshore
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    raffshore Junior Member

    google.com learns me that a are a lot of tripple power intrepid boats, call or mail the factory, they know best
     

  13. IMP-ish
    Joined: Jan 2011
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    IMP-ish powerboater

    Will watch for photos.
    There are all kinds of brackets for connecting the tiebar to the center motor and still turning and tilting ok. I like working with the engine height first. Even with expensive brackets it's still easier than bottom work and it's reversible and less work than the alternatives.
     
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