Re: porpoising

Posted by Jack S (67.242.10.58) on April 09, 2002 at 04:36:57:

In Reply to:Re: porpoising posted by Bill on April 08, 2002 at 17:45:58:

1/2" below the hull is near the surface of the water when the boat is on plane. Big engines on deep vees are normally mounted about 1" below the bottom of the hull. The cavitation plate needs to be underwater to provide the stern lift to get the boat on plane and to keep the prop from sucking air and losing bite. On a performance hull with a big outboard, a hydraulic jack plate is often used to raise the engine once it's on plane and trimmed out. This decreases underwater drag, and with a performance prop, significantly increases speed. Often a lower water pickup needs to be incorporated in the nosecone to maintain sufficient intake water pressure. On any boat however, the cav plate needs to start below the level of the hull to lift the boat on plane. If the cav plate is above the bottom of the hull, the most efficient planing attitude will probably never be reached and the prop will always be running in "dirty" water.

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