SoCal Jet Boats
Tech Talk => Jet Pumps => Topic started by: RiverRatWife on July 24, 2020, 08:42:53 PM
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Porpoising really bad even trimmed down ride plate is level with the hull
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Check you intake it could be set incorectly
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Is this a new to you boat? If not, is the porpoise new and did you make any changes?
I’m not positive,but I think most boats that have a ride plate, have it up a few degrees from keel. I would make small changes to it and see how it reacts to see if you can find the “sweet spot”.
Another thing to check out is the straightness of the bottom of the hull. Take a 4 foot straightedge to the back of the riding surface of the hull. Any bump (rocker) or gap (hook) can affect the ride. Some hulls were designed to have it. But as we started adding power and speed, it affects the ride.
But I would start with the simple stuff like adjusting the ride plate in small increments.
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This boat has an insert pump, so no intake. The ride plates on insert pumps are really more to prevent sucking air into the intake, from the stern, however it is a lifting surface. As Dave mentioned, it should angle up towards the rear, relative to the keel, about 4-degrees +/-.
You could check the bottom for your own piece of mind, but spending thousands on bottom work on that boat is not economically viable.
As Dave inquired, is this a new boat/new problem? Start with the free stuff first.
Does the issue occur when fully-loaded and a full complement of passengers and gear? Does it happen when it is totally unloaded with only you in the boat?
Have you tried making passes with only one or two passengers? Try having them move around to various seats, fore and aft, to see how changing the center of gravity affects stability.
Another possibility is a pump loading issue. Insert pumps are not known for their loading capabilities. Are you aware of changes in RPM, either by observing the tachometer or by listening to the exhaust tone, while porpoising?
One final thought for now, could you get a ballpark angle of your nozzle, at full up and full down, relative to the keel? Full down would be in the range of 15-degrees and that is huge.
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Does it level out when you increase speed?
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