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Thread: Trimming O/B jets for the shallows?

  1. #1
    Moderator LuJon's Avatar
    Join Date
    Mar 2007
    Palmer, AK

    Default Trimming O/B jets for the shallows?

    So after thoroughly beating the snot out of my jet foot in the Matanuska this past weekend I have been researching tricks for staying afloat and moving when running out of water. I continue to be amazed at some of the water that my little wooly slips through but there are times where another inch of H2O would have been the difference between driving and drifting.

    Does anyone trim their jet to get the heel up and make it more level to the hull in the shallows? I have read that it works but can lead to cavitation. While cavitation is bad, trying to crush rocks seems like a much more immediate concern to me. I personally haven't played with it much as I assumed that the tunnel hull nullified the need. After looking closer at the types of hits my foot took however I think that it may be worth some research. I am curious what others are doing in this regard.

    I am also open to any other tricks to keep her pushing!

  2. #2
    Member Akgramps's Avatar
    Join Date
    Apr 2008
    Last civilized place on the planet


    LJ, I have wondered these things myself....trimming the foot back raises the bow on most boats and that doesnt seem to help at all, at least from my experience.

    I am sure WB has experimented plenty with tunnel design but I have often wished the tunnel was another inch taller. On my own boat, using a lift, I can run the front of the foot 3/4"-1" above the roof of the tunnel......w/o cavitating, even on takeoff cavitation is not a issue.

    I have added some pods and extended the tunnel to match the setback of the lift. The bottom of the pods extend over to the sides of the lowest edge of the tunnel, then instead of that skimpy little piece of UHMW I wrapped the top and sides of the tunnel with a rubber flap.

    This setup really helps keep the water directed at the foot, however even then foot is the lowest point and hits first...........but its real close to not hitting so it makes me think its doable to raise the tunnel.

    When I installed the lift, I placed it so I would have some adjustment at the top when using the jet pump, and was pleasntly suprised the first time I tried it and could feel the boat pick up a little speed when I raise it that last 3/4".

    Now, I just run it all the way up all the time......
    “Nothing worth doing is easy”

  3. #3
    Member Music Man's Avatar
    Join Date
    Aug 2006


    Hire TJM to drive it.
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

  4. #4
    Join Date
    Mar 2009
    Petersburg, Ak


    You can motor around all you want with the jet trimmed up while you're off step. While you're on step you're kind of limited with the trim by the bow up action and cavitation as mentioned above. Being trimmed all the way under can add a little stern lift effect and allow you to slow down a bit with some boats. Being able to be on step at slower speeds may help you spot and miss some of those rocks you are finding.
    I also like the band-aide method... do it fast and hope it doesn't hurt too bad.
    Yamaha Dealer
    Petersburg, AK

  5. #5
    Moderator bkmail's Avatar
    Join Date
    Apr 2006
    Palmer, AK.


    On my alumaweld jet I would take off with the foot all the way down. Once on step I would trim it up (3 bumps on the rocker switch) till it's about to cavitate. This would allow me to scoot over stuff with the foot as high as it would go without loosing suction (cavitation). Thus the rear end of the boat would contact before the foot would.
    It's also a fine line for manuevering in hard corners, I would have to bump it down once if I knew I would be weaving or hard conering so it wouldn't cavitate on a skinny corner.
    Just takes practice but it is well worth getting it right if it means damaging your foot or not.
    When in doubt, throttle out!!
    My .02 cents!


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