Cavitation Problem

[ACCEPTENCE]

New to the outboard thing here.
Hopefully someone can shed some light.
If the propeller is catching air and trying to cavitate, would a larger pitch prop reduce this???
With the motor in a vertical posistion and the prop shaft parallel to the bottom of the boat the prop seems to have a bad cavitation problem.
Now if I tuck the motor up tight in a negitive trim posistion the cavitation problem goes away but after coming on plane the front of the boat drives over and plows at the bow. It's even a handful to steer, serious bow steering thing going on.
So the question is: Would a larger pitch propeller grab more water and minimize the cavitation problem even with the motor trimmed and the prop shaft parallel to the bottom???????
Any help and/or thoughts would be great, Thanks Greg.

[Rexone]

Being a whacker owner (don't tell anyone).. possible problems.
Motor height too high causing cavitation.
Prop ventilated too much (some props have vent holes in them or possibly a hub od that is too small compared to the case diameter allowing too much ventilation)
Or just the wrong size prop (too small a diameter and/or pitch)
Or a combo of any or all of the above contributing.
Big help huh. :rolleyes:

[sam pioske]

Originally posted by Rexone
Being a whacker owner (don't tell anyone).. possible problems.
Motor height too high causing cavitation.
Prop ventilated too much (some props have vent holes in them or possibly a hub od that is too small compared to the case diameter allowing too much ventilation)
Or just the wrong size prop (too small a diameter and/or pitch)
Or a combo of any or all of the above contributing.
Big help huh. :rolleyes:
Tell us what kind of boat? engine? Prop.? You must not have power trim or you could just trim in to start - then trim out on plane .02 cents worth

[ACCEPTENCE]

Rex, I'm hoping it's just a prop thing. the water is hitting the lower unit just below the upper plate and above the lower plate, so I'm thinkin the height is on the money. It's a brand new prop that I'm using now and The Anchor siad it was a good place to start, as well it's the same D/P as the one that came with the boat. Lets hope a larger pitch helps it out.
Sam, On the head Sam, The trim/tilt assembly was stolen from the boat at the river so yes, I do not have power trim at this time.
Which by the way would probably solve or at the least help the problem, I think, I hope???
At this point the cost for replacing the entire missing trim/tilt pump assembly is about $600.00, so that's not going to happen right away.
(1980, 85hp, Johnson) Model J85TLCSA.
So do we think with a new 15 pitch on it now and it's working with some cavitation that a new 17 pitch would reduce some cavitation????:confused:
Bigger ears = more water = less air ??? maybe ???
Thanks for your insight, Greg

[V-DRIVE VIDEO]

Acceptance, your running what we call a shortshaft lower end :eek!: You need a jack plate to lower the engine down below the hull line. LOL :D :D

[Lookin for Liquid]

Acceptance......You might want to check the kill switch as those short out and give the feeling of cavatation problems

[ACCEPTENCE]

I should be so lucky for it to be a kill switch. I mean to tell ya when this thing reaches a certian point and starts to cavitate the prop the motor rpm's to the moon if your not on it. I will check it anyhow:D .
Hey there Jer,
The motor was way to low as it was. The water is now breaking right in the place it should as I understand it. But I could be wrong at that.
Someone out ther has had the same problem just hasen't read this thread yet. Watch and see, he'll have the $7.56 answer and I'll be all good then.
HELLO MR. SOMEONE ARE YOU THERE!!!???:confused:

[DUCKY]

Your talking 15 and 17p props on an 85hp motor, your probably talking about a non surface piercing propeller. If the prop is not designed to have a little air around it, then it will slip like a bitch if it does. Unless your running an over-hub racing style propeller, your motor is wayyyyyy too high right now. Most stock style propellers are designed to run with the cavitiation plate (the plate on the lower unit, above the prop) even with the bottom of the boat, but often you can get away with running it slightly higher than that. You also need to think about water pressure to the motor. If you don't have an aftermarket nosecose with a low water pickup, and a water pressure gauge, you shouldn't even think about running your motor that high. I would start out with the center of the top water inlet hole on your lower unit even with the keel (about 5-6" lower than where your are now) and make small adjustments from there to reach maximum overall perfomance. The "water spray hitting the lower unit" means nothing. Water spray doesn't keep your engine cool. Those little holes in the side of your lower unit must be no more than slightly above the bottom of the boat, unless modifications are made. If they are, the engine will overheat, and you'll be spending alot more than $600. Post back, or email me if you have any other questions.

[DUCKY]

And by the way, no a larger pitch propeller won't do you any good.

[sorry dog]

Aluminum prop?
Stainless prop with a bit of cup in it would probably help but sounds like you got other contributing factors as well.
Post a picture of your setup and that well help us see what the deal is.

[ACCEPTENCE]

and it's all good...I put a brand new 17 pitched prop on it and it helped out alot. I can run full throtle with minimal cavitation now.
The motor may still be just a tad high. Maybe 3/4 inch???
Realize this is on a twenty six foot pontoon boat.
When the boat goes over large wakes and swells the motor tries to cavitate a little which leads me to believe the motor is raising up with the boat and introducing air. Any thoughts???
I did get it to run 26mph g.p.s. fully loaded with pumps, air bags, scuba tanks, co2 tanks, generator, rigging chains, come alongs, dive equipment and all that racket. We're talking about a heavy load here!!!
I did add two 1/2 inch wedges under the motor mount tucking the motor further under the boat as well. I think because the motor is acutally at to much of a reverse angle to the pontoons, it's driving the front over and trying to bow steer. Any thoughts???
Thanks, Greg
In the mean time I'll keep tinkering and changing the set up untill I get it right:D :D :D

[CALIFORNIA PERFORMANCE]

Sorry for the off topic Greg but did you sell your V-DRIVE??:(

[ACCEPTENCE]

Hey Marty,
Nah...I still got it, I didn't try very had to push it either. As a matter of fact it's apart right now.
New motor parts, pistons, rings, bearings, blower and some other cool stuff. I am having the entire inside floors and glass done while it's apart too.
It'll be ready for the April/May event.
Take care, Greg

[CALIFORNIA PERFORMANCE]

Cool we will see you there. WE WILL MAKE IT THIS TIME..:D :wink:

[DUCKY]

Well geez, you never mentioned it was on a pontoon. Your probably OK. A pontoon doesn't lift and set on it's running surface, so your prop is buried deeper than you think.