cavitation/ventilation problem

[npd4432]

I have a 1983 Sportcraft Sportsman boat with a 1983 Evinrude 75 HP motor model # E75TRLCTE. The prop is a 13 3/4 x 13 Solas aluminum prop. The motor does have power tilt and trim. When turning at WOT the prop ventilates until you straighten it out again. This only occurres when turning at a moderate to hard turn. The trim is full down and the motor is in its lowest position on the transom. The boat also has smart tabs. Any help to alleviate this problem would be appricated.

 

[WillyBWright]

Re: cavitation problem

Re: cavitation problem

13 sounds too small. If that boat is rated for around 75Hp, I'd expect to run a 17 or 19. If it's rated for a V-6, then I suppose 13 would be appropriate. Make sure the tabs aren't too radically positioned down, but the inside one in a turn is going to lift the back of the boat regardless. That's going to swing the motor further out of the water. Chances are good that your prop isn't cupped. That would help if it were. Plus the diameter is larger and more likely to grab air than the steeper props with a smaller diameter. Frankly I'd expect to see a 13 on a pontoon. I think you need a different prop.

 

[npd4432]

Re: cavitation/ventilation problem

The engine runs perfect within the rpm range with this prop, I also have the 15 pitch factory prop which cannot pull me out of the water when skiing, The 15 pitch also experiences ventilation. The smart tabs helped a little bit with the problem. Are you suggesting I change the diameter of the prop or the pitch? I also do not know how to determine which gearcase I have. When doing a search for my engine a 3 cyl 13 spline is listed and a 3 cyl. "pleasure" is also listed. Which do I have? The model number to the motor is E75TRLCTE.

 

[Almeja]

Re: cavitation/ventilation problem

IMHO:

Outboard plus sharp turn at WOT = risk of ventilation.

Further IMHO: I think ventilation issues are inherent to particular boat/engine combinations. On one of my outboards putting a whale tail on helped a bit, but didn't completely solve the issue.

I simply adopted a driving technique of backing off the throttle a bit in sharp turns. After awhile it became second nature and no more ventilation.

You might look to trying a prop with more 'bite' or cupping but dunno if it will help or not. What are you trying to accomplish with WOT in sharp turns? Are you trying to sling tubers around?

Now I have an inboard/outdrive. No more problems with ventilation.

 

[walleyehed]

Re: cavitation/ventilation problem

It IS normal, to some extent, to get some venting in hard turns, and is magnafied by props with less cup.
There are likely some props out there that will have better technology behind them that will hold better in turns. The design of the hull changes this as well some lift more in turns, some will drop slightly.

 

[npd4432]

Re: cavitation/ventilation problem

I live on a small lake with a "ski zone" which is a part of the lake in a circular bouyed off area so the reason WOT turns are somewhat necessary when pulling a skier because the lake is so short, especially when there are more than two boats on the water to avoid a collision. I have had other boats which never experienced this, just want to know what I can do to lessen the problem. By the way the prop I have on the boat is a 1 year old Solas Amita, purchased here on iboats, with the cupping you describe.

 

[Jdeagro]

Re: cavitation/ventilation problem

npd4432;

You may need to adjsut the smart tabs. If you wish, call me. 800-233-0194

 

[Crownie2]

Re: cavitation/ventilation problem

I am on my third boat and when doing what you describe, they have reacted the same way to one degree or another.

Perhaps the smart tab adjustment will help somewhat - short of trying a new prop, you may have to live with it.