Cavitation problem...prop?

[sundog]

Hello everyone! quick questune. have a 1964 16' evinrude tri-hull with 1978 merc 115hp engine. Once on a plane, anything harder than a gentle turn will start the prop cavitating (starboard is worse than port turn). its obviously not the original engine or prop. Engine is mounted correctly and shaft is right length (plate about 1 inch below keel). Trimming dosnt seem to affect it.<br /><br />any ideas? Im thinking prop not cupped correctly, but not really sure. anything else? skeg is also sheared off half way...could this have something to do with it?<br /><br />also, this is my first tri-hull. seems they should 'skid' in a turn anyway (inside hull not allowing heel into turn?). boat is overpowered with 115, maybe Im pushing boat past design charictaristics?<br /><br />thanks!

 

[Solittle]

Re: Cavitation problem...prop?

What is your rpm at WOT? Post back.<br /><br />What prop do you have now?<br /><br />A 115 is not overpowered if the boat is rated for it.<br /><br />I don't think the skeg comes into play on this.

 

[Jack Shellac]

Re: Cavitation problem...prop?

Sounds like your prop is ventilating, which shows up in a turn like you describe. Usual cause is that it's mounted too high on the transom and air gets introduced into the waterstream on turns. About 1" below keel sounds right, but there may be something else about the hull that contributes to this. If you don't find anything else, you may want to try lowering the motor some.

 

[sundog]

Re: Cavitation problem...prop?

Solittle~ dont know...no tach, but RPM seems to be a little high at WOT. dont know the pitch of the prob, either...came with the boat. I may take it up to the local prop shop and see if they have one I can 'rent' for a day (will also be adding a tach). boat is rated up to 90hp.<br /><br />Jack~ I thought that too...will have to cut the transom down a bit to do that. wanted to explore the prop...or anything else first since the lower unit seems to be sitting right. I just replaced the d*mn transom 2 weeks ago and the thought of cutting it up isnt particularly nice...