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Water Jets; efficiency?

Discussion in 'Technical Discussion' started by cliffandjudiw, Jan 19, 2009.

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  1. cliffandjudiw, Jan 19, 2009
    #1
    cliffandjudiw

    cliffandjudiw New Member

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    I've always been curious about jet drives in yachts. the pro's and cons. I've seen them on small boats like Hinkley or large yachts like braveheart,(i believe). how do they compare for maneuvering,fuel cost,mainteneance,etc.I live in the pacific northwest,usa, and there is a lot of crud in the water. seems like it would pay not to have propellers hanging down to hit it.
    just curious.

    cliff
  2. goplay, Jan 19, 2009
    #2
    goplay

    goplay Senior Member

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    I had looked at a couple of boats in the 80'+ range with jet drives. Very manouverable at both low and high speed. Less vibration than with regular props. The biggest problem is that they are about 25-30% less fuel efficient. Second, they need to be run regularly, since growth can build up in the intakes. This is more of a problem in warmer climates. I have also heard that they aren't as effective as props in rough water but that might be an opinion.
  3. Pascal, Jan 19, 2009
    #3
    Pascal

    Pascal Senior Member

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    Jets are probably attractive in the PNW because of all the dead heads you have up there... they can still damage the hull but wont' rip a shaft or rudders.

    Tehy are also forgiving... I was talking to a guy a few weeks ago in an marina where you normally don't want to come in at night. I asked him how it went, he confessed that he came in by powering the boat over a sandbar having missed the main channel... He clearly woudl have been in deep doodoo with props or pods but I wonder what that did to the impellers!
  4. Capt J, Jan 19, 2009
    #4
    Capt J

    Capt J Senior Member

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    They are less fuel efficient then propellors. They are better when it comes to hitting things such as logs, however you can still damage them pretty heavily if you run aground and suck a lot of sand/smaller rocks etc through the impellors. It is also possible to such debris into the impellor like ropes and so forth.
    I have only run smaller boats with jets and am not super familiar with larger yachts with them. I'd prefer propellors myself.
  5. BMcF, Feb 5, 2009
    #5
    BMcF

    BMcF Senior Member

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    I have designed and helped to build a large number of waterjet vessels; yachts, commercial and military. Jets have their place and for high-speed vessels can be equal to or even better than fixed-pitch props in terms of propulsive efficiency. Their advantages for low-speed maneuvering and low vibration (again, more so in high-speed applications) have been noted already above.

    In the range of speeds for which most yachts are designed to operated, most particularly, their maximum-range cruising speeds, the good ole fixed-pitch propellor can be a great deal more efficient than a waterjet propulsor.
  6. YachtForums, Feb 5, 2009
    #6
    YachtForums

    YachtForums Administrator

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    Which is exactly what I tried to convey to Capt. J when he originally joined YF... Jet vs. Prop
  7. BMcF, Feb 6, 2009
    #7
    BMcF

    BMcF Senior Member

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    And you stated it much better than I... ;)