Doel-Finn question

[moxieman]

How well does the Doel-Finn help cavitation on a 25 Mercury?

 

[Chris1956]

Re: Doel-Finn question

Moxie, Assisting with Cavitation (actually ventilation) is not a function of a Doel-Fin. Doel-Fins are supposed to help you get on plane faster. If the motor is installed correctly, they should have very little effect at high speed. If you are ventilating, they either your motor is installed too high on the transom, or the trim angel is too great.

 

[Silvertip]

Re: Doel-Finn question

Or you have a short shaft engine on a boat that requires a long shaft engine. Check the position of the antiventilation plate (the plate just above the prop) in relation to the bottom of the boat. It should be flush or an inch or so above the bottom of the boat. Lower is fine but you get optimum performance if flush or just a bit higher. If the AV plate is higher than that, the engine is mounted too high or its the wrong motor for the boat.

 

[Silvertip]

Re: Doel-Finn question

Or are you confusing cavitation with porpoising (nose of the boat bounces at high speed). Ventilation (confused with cavitation) is when the prop loses its bit and seems to slip. This can also be caused by a spun prop hub.

 

[moxieman]

Re: Doel-Finn question

how much can the motor be for it to be optimum before it gets to high, 2 inches?

 

[Silvertip]

Re: Doel-Finn question

The answer is "the setup is optimum when you have maximum speed, the engine rpm is at the manufacturers wide open throttle rpm and the prop does not blow out (ventilate) and you don't lose water pressure". It depends on the engine, boat, the prop type, the load, and engine mounting height. If you have a short shaft engine on a boat that requires a long shaft motor, it doesn't matter, its already too high. Another factor in having an engine too high is that the water inlets cannot get any water so the engine runs hot. If you have the proper shaft length, two inches may or may not be a problem. It's a trial and error situation.

 

[moxieman]

Re: Doel-Finn question

thanks for all the help!! I will have to try what you guys have said!!