Mermaid turbo four/pp90 jet

Discussion in 'Jet Drives' started by Seabear23, Oct 31, 2015.

  1. Seabear23
    Joined: Oct 2015
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    Location: Sweden

    Seabear23 New Member

    I recently bought a used Seabear 23 mob boat in terrible condition, i belived it would be a perfect winter project. And it will be maybe moore then one winter? I have taken the whole boat a part to rebuild it a little different, mainly Widen the center console and making some seats on the engine compartment. So far no problems! Problem is i have two Ford mermaid turbo four 150hp that does not run, one has drowned and isnt ever going to run, the other one has run on 2,5 liters of oil insted of 9,5 and has gotten an restoration that wasnt good. Still doesnt sound well. Now i wonder if i find a 6cyl mermaid, will it fit on the original engine bed? Do i need to change the original impeller? I was thinking 200-250hp. According to maritime-partner the boat will increase speed to about 37kn.

    This is my first jet powered boat and i really love it althoght i doesnt float. So please give me some advice.
  2. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    The pump power is proportional to rpm^3, which means that if you want to use 250 hp instead of 150 with the existing impeller, your 250 hp engine has to produce its max power at (250/150)^(1/3) x the rpm of the original.

    With a Mermaid 6 as a substitute that is not realistic, so you need a different impeller with higher pitch.
  3. Seabear23
    Joined: Oct 2015
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    Location: Sweden

    Seabear23 New Member

    Thanks for the answer! i suspected something like that, the boat came with a diagram that suggested that jet wanted 4500 rpm @320hp. if someone have the need for papers regarding pp90 jet or mermaid Engines i have lots of them.
  4. Thunderbird 1
    Joined: Jul 2017
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    Location: Australia

    Thunderbird 1 New Member

    I have a PP90 in a RIB, any information you have on the PP90 you could send me would be very helpful

  5. Magnus W
    Joined: Nov 2017
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    Location: Sweden

    Magnus W Senior Member

    I have a Mermaid Turbo Plus and while it's rugged enough I get the feeling it really doesn't like sustained high rpm. Also, as a general rule, old diesels don't appreciate high rpm/low load (which is what we're talking about here, yes?)

    Perhaps there's a better choice of engine for you?
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