cavitation.....

[uncwillie]

i get persistent cavitation just before coming onto a plane with my 8 hp Evinrude on a 9 foot Caribe hardbottom (older step type) RIB. The prop seems to be stock, in reasonable shape, and the motor is now tilted toward the transom all the way because nothing else was better. It's just like you threw a plastic bag over it! If i ease vvvvery gradually up on power, i can get it on a plane, and it's fast there.<br /> -Perplexed

 

[fireman57]

Re: cavitation.....

Moderator: There were some cavitation questions on Johnnyrude repair forum. Would he get better results there?<br /><br />uncwillie, welcome to iboats.

 

[JB]

Re: cavitation.....

I think this is a question that fits all outboards and is not a trouble/repair problem.<br /><br />This is the right place for it.

 

[ddaigle]

Re: cavitation.....

Is there any way to lower the motor? If not a prop with more cup will help. I doubt they make many varieties of prop for this motor, but you can try. I have a 6 hp and it will do the same thing if the motor is raised just a little.Is the motor a short shaft on a boat that needs a long shaft?

 

[Ross J]

Re: cavitation.....

You've most likely checked Jim but is it possible the hubs spun? I only say this because you point out that she planes if you button off a bit.<br />Ross

 

[uncwillie]

Re: cavitation.....

The water behind the boat is pretty well churned, Ross, so i think it must be cavitation. Is there a quick check on the prop i can do myself, besides lokking at the general condition, like missing blades? ;-) thanks

 

[TwoBallScrewBall]

Re: cavitation.....

Mark a line on the back of the prop hub, on the parts on both the inside and outside of the rubber bushing. Take a ride and make it cavitate. When you get back look at the line. If it's not lined up anymore, you have a spun hub.

 

[Snowdrggn]

Re: cavitation.....

If I am not mistaken, the 8hp uses a shear pin, not a shock hub. (My 1986 8hp does anyway...)

 

[Scaaty]

Re: cavitation.....

You can take the prop off and take it to a prop shop (through a boat dealer) and see if they can cup it a touch.

 

[uncwillie]

Re: cavitation.....

Robby, can you cup an aluminum prop? It does have a shearpin on this motor.

 

[rodbolt]

Re: cavitation.....

hello<br /> even with a shearpin it has a hub. if the hub is not spun then I am thinking its ventilating not cavitating. most 8hp motors dont have enough power to cause cavitation. look for any obstructions in front of the lower unit that will disturb the water flow.<br /> and make sure the ventilation plate is about 1" below the boat bottom.

 

[rodbolt]

Re: cavitation.....

a PS<br /> I have plans to be in caracas and rio chico and margarita at christmas. we also want to stop in puerto la cruz. my fiancee has a job lead for me at some marina there.<br /> good luck and keep posting

 

[Ross J]

Re: cavitation.....

The water behind the boat will look well churned. Spun hubs often don't "let go" till the pressure builds up to a certain amount so the prop will look and behave like it OK untill it gets to the amount of pressure it takes to spin. Each time you slow down it gets it's grip again and appears OK. <br />I guess the best way for you to check would be to borrow a mates or the shops prop of the same specs and run that. You'll get the answer for sure. If it's cavatation then it'll do exactly the same with the borrowed one. If it's the hub spun then it'll push your boat along well enough.<br />Ross

 

[uncwillie]

Re: cavitation.....

rodbolt; i plan to be outa here by end Nov., otherwise i'd love to meet you. Puerto la Cruz is a nice place to stay, and i'd be glad to give any particulars you like about the marinas here, etc. Margarita is the best shopping; duty free!

 

[BillP]

Re: cavitation.....

Could be your motor is mounted too high. Does it also cavitate when doing sharp turns at high speed? If so, check the cavitation plate and see if it is higher than the boat bottom. Speed comes with the higher prop...and so does air.