Alternative power for a Jetski Hull

Discussion in 'Boat Design' started by pistnbroke, Jan 16, 2009.

  1. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    I have just purchsed a $120 jetski hull (Yamaha ) with the intention of towing it to the local everglade system here in Noosa Australia and then cruising the waterways ( speed limit 6 knots) I have fitted it with a transom . Moved the seats forward 8 in to adjust the balance issue and have a 15 inch outboard well of course fibre galssing over he jet slot underneath ..Ballast may be neccessary for stability .. I intend to use my Briggs and stratton 5 HP outboard but am considerering a 6.5HP electric start 200 cc I can get from ebay and then to fit a shaft to a propeller via a chain drive and clutch from a go cart .( engages 2250 rpm) ...The dry weight is 100kg ( 220 lb)

    You all seem so well informed on here I wonder if you have any suggestions the way its called
  2. chabrenas
    Joined: Jan 2009
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    Location: France

    chabrenas Mike K-H

    I'll leave you to worry about the propulsion system. My concern is that 5-6 knots is an uncomfortable speed for that hull - not fast enough to plane properly, so making a big hole in the water. I suspect that you could putter around the swamp at 3-4 knots without needing as much as 5hp (I'm thinking back to the Seagull-powered tenders of my youth).
  3. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Hi pistnbroke,

    A typical Yamaha Waverunner would be 10 feet or so on the waterline, and will start riding up on its bow wave at four to five knots. In that attitude it'll likely be uncomfortable and hard to steer, and will start to drag a substantial wake behind it. It won't level out and run nicely until 12-15 knots, maybe more.

    If you stay below 4 knots or so, as chabrenas says, you'll only need a tiny engine, 5 hp would be more than plenty, and it should run smoothly and without much fuss. An air-cooled Briggs might be a bit noisy for wildlife watching though.
  4. robherc
    Joined: Dec 2008
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    Location: US/TX

    robherc Designer/Hobbyist

    Heck, with a 4knot speed limit before you start losing efficiency, I'd be tempted to throw a deep cycle battery in for ballast, and run a trolling motor off it! Plus you'd get the (big) benefit of running in near silence, so wildlife won't even hear you coming!

  5. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 34, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    Well I have got a seagull ..useless thing and too difficult to handle in the limited space....speed limit is 6 Knots ....also have minkota but 3 mph is all it does on my canoe so gets tedious to go any distance . .. a 20 hp Tohatsu would get it to shift .....but I dont want to tear about nose skywards!

    Really needs a system that put the weight nearer the front hence the thought of a 6.5hp and a propeller shaft driving an easy to get right hand prop ..clutch and bike chain drive at about 2 to 1 . Motor is US$ 150 electric start and battery inc ! I have the clutch (new) and a lathe...

    its 9 feet long ( 2.7m)
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