Adjusting hieght of outboard?? How do I know

[parrisw]

Ok, I got a 16' Johnson Trihull, with a 1984 115Johnson, and in turns at speed, I get allot of prop slip? Cavatation? I can hear the prop speed up, then straighten out it catches and then no more slip, its better if I slow down turn in then back on the throttle. Could it be that my motor is too high?? Would a hydrofoil help?

Thanks!!

 

[soundman2424]

Re: Adjusting hieght of outboard?? How do I know

Sounds exactly like your engine is mounted too high. No, a hydrofoil would not help. Do you have space to lower your engine?

 

[parrisw]

Re: Adjusting hieght of outboard?? How do I know

Sounds exactly like your engine is mounted too high. No, a hydrofoil would not help. Do you have space to lower your engine?

I think I maybe have another 1" I can lower it, maybe a little more.

 

[allpoints360]

Re: Adjusting hieght of outboard?? How do I know

Check the cavitation plate's parallel with the bottom of the boat. Depending on the top speed of the boat, you should be parallel or slightly lower.

Lowering just a little can make a big difference.

 

[tashasdaddy]

Re: Adjusting hieght of outboard?? How do I know

when you go into a turn it increases the load on the motor, and attitude of the hull, slow down, then enjoy your speed, or do not make the turns as sharp.

 

[parrisw]

Re: Adjusting hieght of outboard?? How do I know

Thanks guys, I'll take a pic then post it up, you can judge. I'm guessing the top speed is an easy 45mph, maybe a little more if trimmed right.

 

[parrisw]

Re: Adjusting hieght of outboard?? How do I know

Well it looks like its slightly below to me.

 

[afr]

Re: Adjusting hieght of outboard?? How do I know

Well it looks like its slightly below to me.

hi guys scott here the proper hight is 1 1/2 inches above the bottom of the boat
go up one hole cavatation is more than likley from an obstruction throwing air into the prop have the prop checked by a prop shop to make sure its ok

 

[BLU LUNCH]

Re: Adjusting hieght of outboard?? How do I know

That motor needs to be dropped your cavitation plate need to level or just under the lowest part of the stern.

Ventilation

Ventilation is a phenomenon that occurs when surface air or exhaust gas (in the case of motors equipped with through-hub exhaust) is drawn into the spinning propeller blades. With the propeller pushing mostly air instead of water, the load on the engine is greatly reduced, causing the engine to race and the prop to spin fast enough to result in cavitation, at which point no thrust is generated at all. The condition continues until the prop slows enough for the air bubbles to rise to the surface.[4] The primary causes of ventilation are: motor mounted too high, motor trimmed out excessively, damage to the antiventilation plate, damage to propeller, foreign object lodged in the diffuser ring.
[edit] Cavitation

Cavitation as it relates to outboard motors is often the result of a foreign object such as marine vegetation caught on the lower unit interrupting the flow of water into the propeller blades.

 

[parrisw]

Re: Adjusting hieght of outboard?? How do I know

Ok, I think I'm confused now. Which is the cavatation plate? I always thought it was the lower one? So my motor is too high?

 

[parrisw]

Re: Adjusting hieght of outboard?? How do I know

Ok in this pic which one is the cavitation plate? If its the lower one then yes its slightly below the keel. So what do I need to do here if anything??

 

[parrisw]

Re: Adjusting hieght of outboard?? How do I know

bump

 

[a70eliminator]

Re: Adjusting hieght of outboard?? How do I know

The lower one is the cav. plate upper one is just to deflect the water from spraying up, I played with engine height on my MFG and if the cav. plate was even 1" higher than the keel my prop would slip like crazy, so it all depends on the hull design and prop performance, the best results for me was the cav. plate about an inch below the keel, just about like your maybe a little lower.

 

[parrisw]

Re: Adjusting hieght of outboard?? How do I know

The lower one is the cav. plate upper one is just to deflect the water from spraying up, I played with engine height on my MFG and if the cav. plate was even 1" higher than the keel my prop would slip like crazy, so it all depends on the hull design and prop performance, the best results for me was the cav. plate about an inch below the keel, just about like your maybe a little lower.

Ok, thank you, mine is slightly below, don't think its an inch bleow though, there is one hole of adjustment left, maybe I'll drop it and see what happens.