Add a Jet Drive to Diesel inboard for additional thrust?

Discussion in 'Jet Drives' started by ColdSteel, Jul 3, 2022.

  1. ColdSteel
    Joined: Jul 2022
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    Location: Connecticut, USA

    ColdSteel New Member

    Hi everyone. I have a 37 foot flybridge with semi tunnelled props, twin diesels. Has anyone ever added a jet drive between dual props for additional thrust? Pic attached, looks like a lovely space beteen the props for a non-swiveling jet. Since I am not an engineer or boat designer...tell me why this would or would not work...thanks!

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  2. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Do you have room for a third engine?
  3. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Blueknarr has asked you an important question above - there does seem to be a 'lovely space' between the props, but inside the hull the steering gear would be in the way of the jet surely?
    And the intakes of jet drives can be very fussy re their location - look at that 'deep vee' (for want of a better description) between the shaft tunnels - how would you propose to fit a jet intake in this area?

    What make of sports fisherman do you have, what engines / power does she have, and what is your usual cruising speed?
    And how much faster do you want to go, re the additional thrust required?
  4. ColdSteel
    Joined: Jul 2022
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    Location: Connecticut, USA

    ColdSteel New Member

    Sealine 360 Statesman so a pleasure cruiser. It has volvo penta kamd43p diesels, 230 hp each. Cruises 19 knots, WOT is 22 knots. There is a deep lazarette in the cockpit. Generator is centered in the back of it, approx where an additional engine could go. I happen to have an extra yamaha MR1 HO 160 hp engine, in a box, from my jetboat. Smaller than the generator, so i think it would fit. I agree the V hull could be problematic. I put two more pics up, so you see the bottom of the hull further forward. How much faster would I like? No specific number...just floating ideas.

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  5. ColdSteel
    Joined: Jul 2022
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    Location: Connecticut, USA

    ColdSteel New Member

    Intake grate on the bottom of the jetboat, not too wide... Seems like I coul put a similar sized intake grate on that v ?

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  6. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Between the large spurs in front of the propellers and the big zincs right in the water flow, I see a knot or so that could be recovered painlessly.
    There is generous clearance in the propeller tunnels, some exploration engineering of gearing and propeller might help.
    Gas turbine motors are sometimes used as a “hyperdrive “ centerline thruster, with a surfacing propeller, and are very effective!
    DogCavalry likes this.

  7. rangebowdrie
    Joined: Nov 2009
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    Location: Oregon

    rangebowdrie Senior Member

    Back in the days of Vietnam the Uniflite PBRs, (~31ft.,) used a pair of 6V-53 Detroit Diesels driving jet pumps.
    They were a pretty compact package.
    Once in a while they show up in Boats and Harbors.
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