Any thoughts on cavitaion on my whaler

[gordwa]

Hello all....I have a 1985 Boston whaler Montauk with a 1990 90hp Johnson that I just did a rebuild on this winter.Its got a ss 13 3/8 x 17 prop.The motor runs great. when I hammer down out of the hole it feels like im doing a burn out in a car and I have to come off the throttle and ease back on to get a good bite.It spins top end around 5500 rpm with no slippage felt.I feel no slippage really any place other that hard hole shots.It was recommended to vent the prop to see if that would solve the issue.Does this sound like maybe a good cure.Or am I needing a different prop....Thank for any input

 

[MikDee]

Re: Any thoughts on cavitaion on my whaler

It sounds like the prop is spinning on it's rubber hub when under most stress (hole shot). Mark the prop with a straight line from a magic marker all across the hub. From the spline to the edge of the hub. Then take it out, & try it to see if any part of the line has moved? If so, you need either a rehub from a propshop, or a new prop.

 

[Texasmark]

Re: Any thoughts on cavitaion on my whaler

Is your prop ported; sounds like just what porting does? If so that very well could be the ports and apparently they are too large for your application. Some props are deliberately ported (a hole drilled under and just back from the leading edge of each blade) to do just what you are experiencing, but the size has to be matched to the load. The larger the hole the larger the gas bypass, and the thrust is decreased a given amount. At higher speeds the holes are sealed off by water pressure and you don't know they are there just as you mention. 5500 rpm at WOT tells me you have the right prop otherwise.

If yours is a factory port job, some prop mfgrs. supply plug in port restrictors to allow you to select the size that fits your application by just changing the ID of the plugs they offer. I know the Laser II does.

HTH,
Mark