Waterjet Handling

Discussion in 'Boat Design' started by SparkyDog, Jul 20, 2004.

  1. SparkyDog
    Joined: Jul 2004
    Posts: 6
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    Location: Oregon

    SparkyDog Junior Member

    I have a '74 Apollo 18' skiboat with a stock Berkeley waterjet. The boat does OK in straight but in a tight turn it handles poorly and also cavitates the impeller. This (in my opinion) is because the hull slides sideways and the intake for the jet has two tall fins on each side of the intake that serve as nice dams against the intake water in a hard turn. I am about to do some significant changes "just for fun." I am going to move the engine about 2' forward and add some hull fins below the CG just as with most modern prop ski boats and wakeboard boats.

    1st question: Has anyone ever done something similar with a waterjet and does the presence of the hull fins 4' in front of the water intake mess up the flow to the impeller?

    2nd question: Has anyone ever removed/reduced the intake fins on the Berkeley jet? If so, does it help or hurt?
  2. Parke

    Any disturbance in the water intake can cause cavitation- I would imagine your theory is correct in your turning problems. You might try & copy the intake on more modern jet drives such as Hamilton & Ultra. Be careful moving the engine forward... the jet doesn't have the ability to push the bow up so a mount further aft is more desirable.
  3. SparkyDog
    Joined: Jul 2004
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    Location: Oregon

    SparkyDog Junior Member

    Update to this post - doesn't look like it is the most popular one of the site;) but in case anyone cares...

    I did make all the changes I described. I cut the skegs off the sides of the pump inlet and I moved the engine forward 20". Yes cutting the skegs off solved my cavitation problem.

    The engine relo was in order to improve the human factors layout of my interior and try to setup the hull to function more like a tournament skiboat.

    Now the motor is at or very near the LCG but as everyone would suspect the hull stays lower in the water than before the relo. Handling has not changed at all other than now that the pump is no longer cavitating in a medium to hard turn, so I can throw high G turns with no problem. :p

    Since I still waterski (I am the only one on the river that still does this) I am happy with my setup. The hull throws a very flat wake. The only other things I may try are adding turning fins ala tournament skiboat and a droop snout to get the jet thrust a little lower and try to raise the ride height out of the water a bit. I will not be setting any new world records for top speed tho.

  4. TollyWally
    Joined: Mar 2005
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    Location: Fox Island

    TollyWally Senior Member

    Thanks for the update. Always good to learn from real world experiences.

    I've noticed around here only old guys waterski anymore. As an old guy it is actually pretty cool. Back in the day you always had to fight other boats for clean water. Now any other towboat you see is throwing a fat wake and moving pretty slow. So you hit one wake and you are past them into clean water. They don't care about your wake, so all is good. Works for me! :)
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