Jet drive for displacement boat

Discussion in 'Jet Drives' started by valery gaulin, Apr 18, 2018.

  1. valery gaulin
    Joined: Jan 2017
    Posts: 172
    Likes: 3, Points: 18, Legacy Rep: 7
    Location: Montréal

    valery gaulin Senior Member

    Any discussion here about Outboard jet drive for displacement boat (Sailboat). Can't find any helping info if it was tried and what was the overall efficiency compared to a standard prop outboard.

    Thank you
     
  2. fredrosse
    Joined: Jan 2005
    Posts: 326
    Likes: 16, Points: 28, Legacy Rep: 56
    Location: Philadelphia PA

    fredrosse USACE Steam

    For the slow displacement speeds, a jet drive is in the vicinity of half the efficiency of a propeller drive or worse. A large slow turning prop is best for efficiency, but as a sailboat auxiliary compromises are made. The outboard prop (small) reduces propulsive efficiency compared to a properly sized propeller, and an outboard jet significantly less again. The advantages of a jet, mainly its safety, is the only possible advantage here that I can think of.

    Very rough numbers, with many details needed to firm up the results, say a 2 ton/22ft LWL sailboat with a 16 inch diameter prop, about 2-1/2 horsepower needed to make 6 knots. With a 9 inch outboard prop, 5 horespower needed, and with an outboard jet, about 10 horsepower needed.
     
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