Outboard Jet

Discussion in 'Jet Drives' started by Oyvind, Sep 6, 2019.

  1. Oyvind
    Joined: Jan 2003
    Posts: 39
    Likes: 2, Points: 18, Legacy Rep: 63
    Location: Norway

    Oyvind ulstein.com

    Dear all,

    We are building a series of Al workboats, Loa=26ft, B=9ft, deadrise @ transom 19deg, weight 5700lbs. The boat tops out at 39-40mpg with a Honda 250 OB and comes on plane easy with little bow rise.

    We have a client that would like our boat with a Honda 250 rebuilt to water jet. I assume that the boat probably is borderlining possible/ not possible, but do any of you nice people have any experience with rather heavy boats powered by outboard water jets? Our client does not require speeds above 20 mph, and wants the waterjet just to avoid ropes in the water. I'm considering twin 150s and/ or modifying the bottom to include a small CL ski and also include water jet side scoops and an outboard bracket

    Thank you for any help!
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Might be easier to fabricate a cage/shroud to fit the lower unit of the outboard, such as is used by lifesavers with IRB's to avoid chopping up swimmers. You'd have to create it is such a way that the rope can't slip through the grille. Give it some rake so that the rope slips underneath, rather than hooks up. Needless to say, such appendages play havoc with the speed potential, but at relatively sedate speeds, not such a huge impost, and won't have a great effect on getting on plane. Probably better to have a five-bladed prop as well, as the prop is not working in the "cleanest" of water with the ironmongery around it. 4prop1.jpg
     
    Last edited: Sep 6, 2019
  3. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    What leads you to believe that the 250 with a jet drive wouldn’t be up to the job if a propeller unit can push it at 40 mph? There will be other issues with efficiency and handling and noise that your client should be taking into consideration as well.
     
  4. Tungsten
    Joined: Nov 2011
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    Location: Canada

    Tungsten Senior Member

    Biggest OB I’ve seen are 150hp so 105 hp at the jet so two would be close. Hole shot power is slow to respond when compared to a prop. Add in a heavy boat. Now a super charged 450 hp inboard maybe a little better.
     

  5. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    There are 300 hp outboard jets.

    You will lose at least 30% of the HP going to a jet, and they are very load sensitive. A Heavy boat with a 19* V may not be a good candidate.
     
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