Which jet for 17ft boat

Discussion in 'Jet Drives' started by nimblemotors, Dec 19, 2012.

  1. nimblemotors
    Joined: Jun 2009
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    Location: Sacramento

    nimblemotors Senior Member

    I'm going to be putting a jet in my 17ft open bow v-hull boat.
    I plan to use a small engine in it, say 150hp, and don't need it to go any faster than 40mph.
    It looks like my only two options for a (cheap) jet seem are the old v8 berkeley's, seen many for sale under $500, and the newer jetski's, they seem to be under $300, and I have a big 3-seater kawasaki as a potential donor.
    The jetski's seem too small, the berkeley's too big. Is bigger better than too small? Holeshot is more important than top speed, so from what i've read bigger is better, but not sure I'll have the torque from a 3-cyl.
     
  2. El_Guero

    El_Guero Previous Member

    Well .... Kawasaki lists their 3-seat jet ski at 300 hp .... so, how would a Kawasaki 3-seat jet ski drive train be too small?

    But, the first question would be, IMHO, what hp specifications were your boat built to?
     
  3. johneck
    Joined: Nov 2011
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    Location: New England

    johneck Senior Member

    The key is also going to be RPM. The jetski pumps are designed to turn up to the 6000 RPM range.
     
  4. nimblemotors
    Joined: Jun 2009
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    Location: Sacramento

    nimblemotors Senior Member

    The 3 seater I have is an older one, 130hp 3-cyl.
    The original engine in the boat was 120hp 4-cyl.

    If I swap the entire drivetrain, the jetski engine and pump, they match,
    but a jetski is designed to go 55mph, I don't need or want that top speed.
     
  5. johneck
    Joined: Nov 2011
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    Location: New England

    johneck Senior Member

    The good thing about jets in that they are less sensitive to inflow speed than props. So if your boat is able to reach a reasonable speed, it should be OK. Hard to say what that is exactly, but if your engine gets near rated RPM, you are probably OK.
    You could also look at changing the impeller to a lower pitch impeller if find that you are not reaching rated RPM.
    Are you planning on taking the whole inlet from the ski as well? You could probably do that and graft it into your boat.
     
  6. El_Guero

    El_Guero Previous Member

    What was the weight of the jetski?

    What is the weight of the boat?

    Does the boat get up on plane with a rated outboard?

    What speed did the boat do with a rated outboard?

    What is the 'wetted' front end of the boat?

    From what little you have given, the jetski looks to be about a match. And I think you might be looking at a top end no more than 24 to 28 .... And that is if you can keep the all the engine weight to the rear ....

    Just a hunch, but I think you are trying to push 3 to 4 times the weight with 2 to 3 times the wetted area in front.
     
  7. El_Guero

    El_Guero Previous Member


  8. nimblemotors
    Joined: Jun 2009
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    Location: Sacramento

    nimblemotors Senior Member

    >> What was the weight of the jetski?

    700lbs

    >> What is the weight of the boat?

    800lbs

    >> Does the boat get up on plane with a rated outboard?
    yes

    >> What speed did the boat do with a rated outboard?

    35mph, it was an inboard/sterndrive

    >> What is the 'wetted' front end of the boat?
    it is a v hull

    >>From what little you have given, the jetski looks to be about a match. And I think you might be looking at a top end no more than 24 to 28 .... And that is if you can keep the all the engine weight to the rear ....

    >> Just a hunch, but I think you are trying to push 3 to 4 times the weight with 2 to 3 times the wetted area in front.

    A 3-seater jetski is what I call "half a boat", they are very large,
    but it is still only "half", my boat is a full boat, although it is somewhat small,
    which is what I like about it, my 18ft was a bigger.

    I can graft the jetski intake onto my hull, probably what I'd do if I use the jetski jet, but the jet seems quite small, they are what 5-6", whereas a berkeley is 10-12", that is a rather large difference.
    The jetski parts are much cheaper.

    I'm thinking if I put in a loader grate into the jetski, it would increase the holeshot but lower the top speed, which is the tradeoff I want,
    but could do the same with the berkeley.
     
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