evinrude 50 hp cavitation height?

[phatmanmike]

ok ok ok before i start, ive read some other posts, and i know im gonna get 37 different answers, but here goes anyway...<br />1986 bonito center console, 1980 50hp evinrude 2cyl, 12.5 diamater X 13 pitch prop(brand new prop) cavitates when attempting to plane or when rpms get high near wot. motor spinsbadly when it shouldnt. my plate, whether its called anti cavitation or ventilation, whatever, you know the one, is about .75 inches above the bottom of the "v" in the hull... where should this be and what can i do to stop cavitation.. would a whale tale help, smart tabs? anybody have this same setup?

 

[rickdb1boat]

Re: evinrude 50 hp cavitation height?

I think you should lower the motor, so that it is even with the bottom of the hull(Cavitation Plate). Then see how it acts before you start putting the fin on. Odds are the fin will help now, though. Some consider the fin a "PAtch" fix, but I have seen them work many times to improve handling and hole shot, as well a ventalation problems. Just my thoughts...

 

[Dhadley]

Re: evinrude 50 hp cavitation height?

Agreed. A "fin" will help. The motor is too high for the prop you have now. <br /><br />There is no one "correct" height for all situations. The technology built into your prop is the formost factor. There are many others that will eventually determine where your particular prop will run best.<br /><br />Good luck!

 

[phatmanmike]

Re: evinrude 50 hp cavitation height?

rb, how do i "lower" the motor, its already on the lowest holes in the mount brackets, and as far as being trimmed down all the way, there is a lil rod that goes through the 4 holes at the base of the motor that could be swapped down one hole, but its rusted in there, any ideas on this.. is it needed? can i cut it out? ive read about cutting the transom, and i just wont do that ...

 

[Jdeagro]

Re: evinrude 50 hp cavitation height?

I agree with the others on one point. Drop the motor. It may be difficult because of the rust but some chemicals could help loosen things up. <br /><br />As would be expected, I do not like the hydrofoils as they will likely cause handling problems at higher speeds. They continue to lift more and more the faster the boat is run. This will cause the boat to run bow down.<br /><br />Smart tabs are adjsutable and regulated to a maximum lift in a number of ways especially at top end.<br /><br />I would also look at the boat load and balance, it may be front end heavy.

 

[rickdb1boat]

Re: evinrude 50 hp cavitation height?

Nothing against tabs, but I still think you will Ventilate due to the motor being too high. On a 50 HP, A fin is not going to cause any handling problems at high speed, other than reduce top speed and that's a maybe. Might wind up having to trim it out a bit. A little more cupping on the prop will help, too. Forget about cutting the boat up and look for other means to stop the problem. Personally, I would stick a fin on it and try it. Then I would look at getting some cup added to the prop. A jackplate is also an option.

 

[phatmanmike]

Re: evinrude 50 hp cavitation height?

i added a "sea ray hydrafoil" fin from boaters world and it does as advertised... it stays level( plane) but it still has cavitation/ventilation issues(the prop overspins at higher rpms, .. can you have a prop cupped that is not already.. i bought a HUSTLER brand 12.5 diamater X 13" pitch, and if you read any of my prior posts, it cleared up a lot of problems. this is one of those props where you add the hub kits afterwards, not a built in hub.. are these ok? i have an OMC stock prop but it is to big of a pitch, so motor wouldnt turn rpms. <br /><br />now with new prop, it turns rpms, just to easy... so it wont go fast enough to get on plane...

 

[phatmanmike]

Re: evinrude 50 hp cavitation height?

and one more thing, that "rod " i sopke of abopve in the first post that is all rusted, it stops the motor from being trimmmed down all the way... as for the motor height on the transom, its all the way down already

 

[ob15]

Re: evinrude 50 hp cavitation height?

rb, how do i "lower" the motor, its already on the lowest holes in the mount brackets,

Are you saying the motor is mounted using the lowest holes? If so that means it's as high as it can be mounted. if this is the case, you still need to lower the motor. Getting the AV plate closer the your keel will get rid of the ventilation. If the motor is as low as you can get it, I would suggest a plate to lower it.<br /><br />I have the same motor & it seems to work fine trimmed up one hole from the lowest. Trimming down to the bottom hole will help plane and lower speed.<br /><br />P.S. I'm going through the same thing as you but not quite as extreme. I needed to raise my motor one notch (AV plate is about 1/2" above keel). The AV plate was around 3/8" below. Will know tomorrow how it works when I go fishing.

 

[catfish1]

Re: evinrude 50 hp cavitation height?

phatmanmike, sounds like your either going to have to lower the motor, or get a prop with more bite. i'm going to guess that you didnt start having ventilation issues until after you went to the 13pitch prop(less bite). if you could get that trim stop rod into the lower position i'm sure that would help. <br />nautijohn has a point also. if the boat is bow heavy it would be more likely to ventilate.