Inboard engine well for outbaord motor

Discussion in 'Boat Design' started by wudenbote, Aug 27, 2008.

  1. wudenbote
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    wudenbote Junior Member

    Hello fellow wood bost lovers: I am going to build a 20'8" power dory with a 6'6" beam at the sheer. The plans call for a conventional transom with the outboard hanging on the stern. However, I want to build an open well for the outboard motor inside the boat. I would much appreciate any suggestions as to how to determine where to put the engine well. Particularly, what the measurement should be from the inside face of the transom to the rear most face of the engine well. As always, your suggestions are much appreciated.
     
  2. Knut Sand
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    Knut Sand Senior Member

  3. SamSam
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    SamSam Senior Member

  4. rwatson
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    rwatson Senior Member

    You will get a lot of water sloshing up inside the well on the stern 'wall'.

    I think Mr Bolger has done a pretty good job in designs that protect the O/B - he just extends the stern down both sides of the motor, and leaves a clear path behind the outboard.

    For your dory design, I would think seriously about an inboard motor. Sure, you have some disadvantages , but you get a lower CG, a streamlined propeller arrangement and a secure engine location..

    I feel that doing a 'well' with an OB is creating a lot more problems than it will solve
     
  5. bobg3723
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    bobg3723 Senior Member

    We use backtrolling splashguards to keep the majority of the back splash from getting in through outboard engine transom. Search Wavewackers and Whitecaps on the Internets.
     
  6. rwatson
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    rwatson Senior Member

    I cant see how these could help easily. They would keep the water out of the boat, but the turbulence insode the well is a source of drag. You could mount something like that at the bottom of the well, but the water pressure would be considerable, not just a splash.

    A non streamlined solution could make for performance problems.
     
  7. xsboats
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    xsboats xsboats

    I recently replaced planks on a 20 ft Simmons highside . Check out her well details at southshores website, they built her. "Dreamcatcher" has a tombstone shaped cutout in her transom with a two panel slidingdoor that slides up and down with the raising and lowering of the outboard.
     
  8. bobg3723
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    bobg3723 Senior Member

    This is what I was driving at. If water were to gush forth vertically through that engine well like a fire hydrant (I exaggerate, but you get my point), then I would expect to see a roostertail shooting above the height of the set of Wavewackers on my Lund at 25 MPH.
     

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  9. bobg3723
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    bobg3723 Senior Member

    I guess I should have made my comment clear about a backsplash function, but I didn't specify it well. This is what I meant by a rubber gasket functioning in similar manner as my Wavewackers, but fixed to the floor/step of this "marvelous piece of engineering"! :D
     
  10. bobg3723
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    bobg3723 Senior Member

    I think another benefit to this setup is to have some sort of high sided transom and foot step for a choppy sea with the ability to cast nets off the back end and not fouling up on a lower unit. Plus, maintanance can have a quicker turnaround time by having an outboard to remove and replace without the complications and expense of an I/O unit. I don't know if this is a performance pleasure craft. More suited for a small commerical vessel, but git up and go when you need it. Just my two cents.
     
  11. bobg3723
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    bobg3723 Senior Member

    This design does what my Lund attempts to do with an aftermarket backtroll splashguard, but they do it with a tidy flat step (the newer Lunds have a carpeted rear deck surrounding the outboard and a solid transom instead of plexiglass of my Wavewackers.

    Actually, their way puts the outboard closer to where a traditional inboard engine would be situated, unlike on my Lund with it's 75HP Johnson V4 hanging off the *** end. There's more built in bouyancy aft in this design over that of mine.

    Also, you have greater directional control with a simple outboard swiveling its prop at wide angles of thrust and at very slow trolling speeds, forward or backward trollingl
     
  12. bobg3723
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    bobg3723 Senior Member

    I would suggest the best route in the final analysis is taking a tape measure, notepad and camera and go to a boat dealer and start taking measurements of O.B. motor clearances from steering wheel lock to lock, engine tilted all the way up, pinch points for a steering linkages, and electrical and fuel lines. Check these measurements between your choice of outboard and other potential candidates and design clearences for competitive make and model O.B.

    If you a CAD capable kinda of guy, poach some of the public domain O.B. cad files here on Bd.net and whip together a CAD mockup.

    Regards
     
  13. safewalrus
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    safewalrus Ancient Marriner

    Have you seen John Gardiners "Dory Book"? might be worth a look, he's considered the Master on dories and there's some good stuff in there to help!
     
  14. bobg3723
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    bobg3723 Senior Member

    It can get rolly and choppy up on Mille Lacs and this configuration has inspired me to take a look at taking a late 1960's era 18' fiberglass runabout with a dead sterndrive I have sitting on my property and modify its transoml to accommodate an O.B. engine (I 'll have to see if my V4 is a good fit, though,,,hmmm). My Lund is so lightweight that it get's pushed around quite a bit trying to stay on a reef point. Many people prefer ot use lower profile bass boats, but I need the security of taller freeboards, yet not quite as tall as the skiff has, though.
     

  15. rwatson
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    rwatson Senior Member

    Thats a good picture BobG - I understand what you are saying.

    In that example however, you dont have a 'stern wall' in your 'pit'. Its leads out to an empty space.

    I have seen a boat that sunk a 'pit' into the hull for the outboard, and at anything over 3 or 4 knots, had water slopping up over the top of the 'pit', not from the outboard wash, but from the speed of the boat.

    You would get the same effect with a flat bow of similar dimensions, and probably a similar loss in performance.
     
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