cavitation

badams270

Seaman Apprentice
Joined
May 9, 2007
Messages
41
I am having a problem with the boat I have. Its a '82 Avenger 17' w/ a 1968 mercury 1250. The problem I am having is that it feels as though the motor is spinning freely until and takes a longer than normal time to plane. I can give it 1/4 throttle and we start moving, 3/4 throttle it acts as though its cavitating. I am not sure the engine is in the right spot, the tilt (I don't have power tilt). Basically the engine is straight up and down, and not sure how far from the bottom of the boat the prop is. Any ideas?
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: cavitation

The bottom of the cavitation plate should be level with the bottom of the boat and on a deep V not more than 1" above it. You also might have a prop hub slipping mark the prop and the hub test run and ck to see if it's moved first thing.
 

badams270

Seaman Apprentice
Joined
May 9, 2007
Messages
41
Re: cavitation

I thought about the spun prop, and i will check that the next time we are up at the lake. But, once i get it to plane out it runs like hell. Its just out of the hole it feels like its free wheeling. I also have a stupid question, but where is the cavitation plate? Thanks for the help.
 

jebeebe

Petty Officer 1st Class
Joined
Nov 26, 2006
Messages
322
Re: cavitation

The cavitation plate is the plate above the prop. Once the boat is on plane you would have less pull on the prop and it would quit slipping. Comming out of the hole there would be maximum load on the prop..........Jerry
 

badams270

Seaman Apprentice
Joined
May 9, 2007
Messages
41
Re: cavitation

Ok, it appears that the cavitation plates is more than 1 inch above the bottom of the hull. And it doesn't look as though I can lower the motor any. The transom is 20" and the motor appears to be a 20 also. How can I get the motor lower in the water. Maybe 2'' lower, to be even.
 

old-gubbins

Petty Officer 3rd Class
Joined
Jul 3, 2006
Messages
81
Re: cavitation

Hi

There is a vast amount of information on this forum, from very knowledgeable folk, just like Laddies. If the cavitation problem is not new, which might rule out the spun prop, search the forums for choice of prop, because some are far less prone to cavitation than others, and jack plates, which hang the engine off the back of the transom.

I don't know anything on these subjects, but they might be worth investigating.

Hth
 

scrobo

Petty Officer 1st Class
Joined
Jul 5, 2007
Messages
277
Re: cavitation

What about notching your transom an inch or 2 down? just an area for te motor...
 

badams270

Seaman Apprentice
Joined
May 9, 2007
Messages
41
Re: cavitation

Would rough edges of the prop cause cavitation? There is a dent on 1 blade, not a big one but it is there. And the other 2 aren't smooth. I'm think I might need a new prop. I know this is an old motor, so where can I find one to buy?
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: cavitation

I would take it to a Mercury dealer, they either need to see the prop or you need the numbers off it so they can tell the pitch, ck on a used one first most dealers have a assortment of used props in the backroom price it and compare the price to new
 

badams270

Seaman Apprentice
Joined
May 9, 2007
Messages
41
Re: cavitation

Yeah, I have tried to find numbers on it. There are none anywhere. I am probably going to winterize it and pull the prop off and see if I can find a good used one this winter. Prices seem to fall drastically in the winter. Our trees up here have already started to change color.
 
Top