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Ventilation

spdrcr03

Member
"Two issues with my 1983 85hp

"Two issues with my 1983 85hp Force outboard. When I turn the boat the motor revs really high and it feels like it isn't getting any bite on the water until I straighten it back out. I read somewhere that that might be ventilation. If that's what it is is there a way to avoid having that happen.

Secondly, when I let go of the steering wheel it turns to the right very quickly. I have my trim tab all the way to the right but it doesn't help. What are other causes for a motor to turn one direction or another? Everything looks fine."
 
"Greg, ventilation is when exh

"Greg, ventilation is when exhaust gasses displace water (in thru-hub exhaust motors - which is the "norm" now).

This displacement allows the prop to spin up quicker, when you first hit the throttle, so that when it does "bite" the water, you get a little better kick than if it tried to move all that water in the first place.

That's designed right into the motor and not much you can do about it.

What you may be experiencing on your turns is possibly cavitation. This is when the water "in front" of the propeller is disturbed etc and leaves nothing for the prop to "bite on".

This could be caused by things such as the shape of your hull or having items mounted too close to the engine (ie. speed pitot, transducer ect). That can be corrected to some extent by moving these "add on's" as far away from the prop as possible.

The pulling to the right can be caused by a number of things including too much weight on one side, a hook or other distortion in hull, a build up of "crud" on the hull and numerous other things - trial and error is usually the only way to solve that issue unless a structural problem is obvious..."
 
"Another cause can be improper

"Another cause can be improper mounting of your engine. The cavitation plate on the motor needs to be even with the bottom of the hull. You don't have a short shaft motor on a long shaft boat do you ??? As far as the pulling to the side, do you have a Doel fin or some other planing aid mounted to the cavitation plate?? I had the same problem with one of my boats. With just me in the boat, the boat would lean to the starboard side. This would call the Doel Fin to dig in and want to pull the boat around. I took the fin off and everything was fine after that."
 
"The cavitation plate is even

"The cavitation plate is even with the bottom of the boat, there was a trolling motor mount device attached to it when I bought it but I took it off when I got the boat home. The holes are still in the cavitation plate but I am not sure if the holes would create any problems.

The motor was trimmed a little high, I moved the trim pin one towards the transom, I haven't tested it yet but I will post here if it helps.

Thanks."
 
"Greg, the holes in the cavita

"Greg, the holes in the cavitation plate shouldn't cause much of an issue.

Lowering the tilt may do wonders - I was out today on Lake Erie and it was a little chopier than I would normally go out in - to the point that because of my tilt angle the prop was almost completely breaking the surface.

This causes it to rev (ok - can deal with that), stop sucking water for a sec (not good at all) and lose forward movement.

Just dropping the tilt by one pin made all the difference..."
 
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