Funjet Kids speed boat project

Discussion in 'Boat Design' started by StonyCreekFarm, May 9, 2016.

  1. StonyCreekFarm
    Joined: May 2016
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    Location: Cullman AL

    StonyCreekFarm New Member

    Hey, I have the hull of an old funjet fiberglass boat and I am wanting to fix it where my kids can put around in it. I need to figure out how to put a driveshaft thru the hull and keep it watertight. Im gonna use a small 6.5 hp horizontal shaft motor and fabricate a drive shaft with a trolling motor prop on the end, but I'm unsure of how to go thru the hull with it. What could i use for bearings/seals/shaft. Thanks for the help.
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    A trolling motor propeller is much too small for the power you intend to use. Also, they are very low pitch for low trolling speeds. The easiest installation would be a small outboard. You can buy a used one for much less than all the parts to make an inboard installation. Also, check the laws for inboard motors. They need to have spark-proof electrics. That includes, point in the ignition, charging system, starter, etc. The boat will also need an exhaust blower. Besides the legal requirements, I'm sure you don't want to see your kids go up in smoke.
     
  3. messabout
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    messabout Senior Member

    Ditto what Gonzo said.
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    You don't want a straight shaft setup, in spite of how simple it may seem to be. First off, they don't turn worth a damn. Second as Gonzo mentioned, you need to setup an inboard properly, so you don't blow up the kids (read really easy to do).

    An outboard or jet are the tickets for a small boat like this. A jet takes up a fair bit of room, inside the boat, but an outboard doesn't. Outboards are cheap and everywhere. Plus you can get them worked on every place too. If you brought a homemade garden tractor engine, straight shaft sort of thing to a shop, they'd just turn you away, not wanting to be responsible for a convolution of bits and pieces.
     
  5. freddyj
    Joined: Oct 2013
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    Location: kansas

    freddyj Senior Member

    I want to do about the same thing for a sailboat because I don't want the weight of the outboard on the transom.
     
  6. messabout
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    Location: Lakeland Fl USA

    messabout Senior Member

    Freddy, Weight is not a problem unless your outboard is a big one. My Tohatsu 2.3 HP outboard weighs 21 pounds. Try to match that with any but the tiniest stationary motor. Much to my initial surprise, the wee little tiddler motor is capable of pushing my 15 foot flattie onto a plane. Admittedly a mushy one but sliding along at a healthy clip nevertheless.

    Stonycreek, you can buy a stuffing box (the through hull part that you need)to accommodate the shaft. Search marine supplier sites.
     
  7. freddyj
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    freddyj Senior Member

    It's not just the weight. I hate the look of an outboard hanging off a sailboat.
     
  8. messabout
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    messabout Senior Member

    Point taken Freddy.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I've put several convention gas engines in boats over the years and the major issues with these are they generally can't be "marinized", so you need to make precautions. The easiest way is to insure the engine compartment is wide open, so fumes won't collect and/or if they do, boat movement will quickly vent them out of the well/box, etc.

    Other issues are these engines (garden tractor, mowers, etc.) are usually made from metals not well suited and very quickly corrode. Carburetors, electrical and exhausts seem most prone to these problems. Coatings can help to some degree, but internals will need constant attention. Heat and noise is also a big problem, as these are usually air cooled. Then there's the exhaust that needs to be routed without burning stuff.

    The last I did was a garden tractor inboard, with a go-cart FNR transmission. The engine came with a big enough stator to charge up it's starting battery and I used 2 blowers, to keep the engine compartment clear. This engine also drives a small fresh water pump to cool the exhaust, which had to go through the planking. The transmission needs to have penetrating oil squirted into it every month to keep it's innards from rusting (shaft seals mostly) and the blowers need to be religiously run or fumes will collect, so they're wired to come on anytime the ignition is activated and have a 5 minute delay (stolen from and A/C motherboard), so they do their job well.

    In short, it's not as easy as you might think and still offers crappy steering (typical of a straight shaft setup), lots of noise and heat. Pound for pound, these setups weigh twice as much as a similar output outboard too.
     

  10. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Put it in a well, perhaps
     
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