'79 Fiberform Runabout Re-power to Outboard

Discussion in 'Boat Design' started by Rocklobster707, Sep 29, 2014.

  1. Rocklobster707
    Joined: Dec 2013
    Posts: 1
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    Location: Chester, CA

    Rocklobster707 New Member

    Hey all new to the site, and first post!
    So I got this 1979 Fiberform 18'-6" Runabout that I want to transform into a pure fishing boat. I really like the lines of this boat, and want to modify a few things.
    So the first thing is I want to re-power from a stern drive to outboard with the use of a outboard bracket. The current motor is good but the VP 280 is shot, and I've never been a fan of those out drives any ways. I would prefer to make the pod myself, so I need some advice, and dimensions. I've seen and read a lot of threads of people making the pods themselves and I love the look.
    After the repower I'll be replacing the floor, and getting rid of the carpet. To make way for some hatches and a nice fiberglass floor with light colored rhino liner!

    So here she ..... "Rocklobster"



    Heres an idea of what im talking about.
  2. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    Well of course the first thing you will need to do is remove the engine and sterndrive. The you need to close up the hole, but before doing that you need to make sure the transom isn't rotted out. I am not familiar with this particular boat but many manufacturers used a wood core in the transom. If water has gotten into the core then it needs to be removed and replaced. In any event you will need to reinforce the transom to make it strong enough to support the weight of a large outboard. The typical sterndrive transom is not strong enough to do this and has to be thickened (usually about 2 inches for a wood cored transom) and support with braces on the inside that are fastened to the transom and the hull. It would be easier to do the sole (what you called the floor) and the hull stringers at the same time so you can fasten the braces to the hull stringers.

    In addition this will change the fore and aft balance of the boat. It will move the Center of gravity farther aft which will affect the boat's trim and performance.

    But as you said, many people have done this, and it is very doable. Personally I would just buy a stock bracket, (probably a gil-bracket) but that's just a personal choice.
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    I'll ditto what Peter has mentioned and include the loads on the bracket/transom interface need to transfer to the hull bottom, which is the point behind stiffening up the transom and any sole stringers that might be there. If you have to screw up, do so on the overly stout side of things, in regard to tabbing the various elements to the hull shell, as the other side of this coin is broken tabbing and other more dire situations.

    The CG question raised is a pretty big concern too, so consider moving tanks and batteries forward to get her to trim out properly. So how far and how much? Well, this is a crap shoot, but when I make this type of change, the first thing I do is find her rough CG, by balancing the hull (full tanks) on a piece of 1" rigid pipe or rod. I move it up and back, until the boat is neutrally balanced on it, then I mark this location for reference. After the major surgery, I do this again, with an eye to move things to get her relatively in the same location. This way the boat will behave as she should underway.
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