motor seems to be cavitating af wot ?????

[tommytoon]

i have a crest 21' pontoon with a 1986 75hp outboard mercury on it. the boat holeshots

great but at wot it revs. adjusting trim is out of the question motor has to be all the

way down. i read on this forum the rubber behind the prop goes bad and could cause

this,marked it with nailpolish and it is not slipping.i have a 3 blade prop that was brand

new when i bought the boat and it is marked 2832 13 im guessing that is the pitch.

motor seems to be in water correctly but i can not lower it anymore. SOMEONE PLEASE

HELP THE NEWBIE THANK YOU IN ADVANCE

 

[quackaddict1]

Re: motor seems to be cavitating af wot ?????

Define the problem better please, is it cavitating or loosing bite?

 

[tommytoon]

Re: motor seems to be cavitating af wot ?????

Boat at wot revs high and i shut it down with throttle,but it does not do it constantly but almost all the time. I guess it may be loosing bite that sounds possible but being a newbie im not sure sorry.i even had all the people sit in back for weight and it still does it if that helps thanks again for any feedback

 

[reddogg]

Re: motor seems to be cavitating af wot ?????

Could be a spun prop. Is the motor mounted to high causing the prop to breack the surface at wot? Does this prop have any cup? A prop with no cup is more likely to slip from what I've been told. Does it only slip in a turn? If so that takes you back to the cup.

Red

 

[quackaddict1]

Re: motor seems to be cavitating af wot ?????

So when it revs high does it loose bite and start to slow down or does it just push past the max rpm while still going fast?

 

[tommytoon]

Re: motor seems to be cavitating af wot ?????

Motor is mounted as low as it can be because motor is resting on the transom but a friend pointed out the plate above the prop is not to deep in the water almost even with the water when boat is at rest just floating

 

[steelespike]

Re: motor seems to be cavitating af wot ?????

You may be looking at the wrong place. Your checking the plate just above the prop.
Ventilation is when the prop losses bite, motor revs and you lose speed.Venting used to be called cavitation.If the antivent plate is near the surface at rest you would likely have venting issues almost as soon as you started to gain speed.
You don't feel cavitation and it doesn't affect bite.
Most motors have holes that you can adjust height with.The main bracket remains against the top of the transom while the motor is raised or lowered.
I don't know if a Short shaft 75 was available in 86 But you might want to confirm it is a 20"(long shaft) motor.
Is it a 3 blade prop? Details would help; max rpm and speed at wot(wide open throttle)
when not venting.