Cavitation Problems

[D river]

I have a 3.9m quintrex sportsman with a 25hp mercury 2stroke on it and it cavitates way more than it should. It does it every time I give it a gutfull or turn a sharp corner up the creeks, it has its original prop on it. Any thoughts on what could be causing this or how to fix it.

[snodger 08]

Lower the motor a notch????

[D river]

Lower the motor a notch????

Do you mean lower it a notch on the trim or on the transom

[Marlin_Mike]

Is it cavitation or aeration round the prop?

Mike

[D river]

Is it cavitation or aeration round the prop?

Mike

Not sure mate it just revs n loses its traction so to speak

[Goochi]

Is it fwd control or tiller steer. Get it up on the plane and look at the leg in the water and see where the cavitation plate is sitting, you may need two people to do this. My guess is that the cav plate will be too high in the water so when you turn air gets sucked under it and your prop loses it's grip. This is the best starting point before you worry about your prop size. You should be able to see the cav plate - and this is a point of dispute depending on who you talk to - either well in the white water behind the boat or just in the clean water under it.
Also if you have your leg trimmed too far out it will generally cavitate easier in turns.

Cheers

[marto78]

Bent or damaged prop or stuffed bush??

[wiz]

How long have you owned the boat?
Has it always done this?
Are the turns at speed?
How many holes out is the motor trimmed out to?
Can you post pics of cav plate level in relationship to hull?

[D river]

How long have you owned the boat?
Has it always done this?
Are the turns at speed?
How many holes out is the motor trimmed out to?
Can you post pics of cav plate level in relationship to hull?

Had the boat 5 months. Motor is on 2nd hole out. Has done it since I put it on there. Turns dont have to be at great speed even moderate pace on sharp turn will do it. Boat came with and old johno so I sold that cause my mate had this motor sittin round his shed for ages its a 2001 model but had less than 6 hours on it n I got it for a steal. I'll get some pics up in the morning

[D river]

And here they are

[wiz]

Motor looks to be correct height. Turns do tend to cause the prop to slip especially if you can't trim in. Had a look on boat sales those tinny's are only small, it must fly with 25hp. what is the hull rated to? When you look over the back when the motor loses grip how far out of the water is the cav plate?

[D river]

Not sure mate I've not looked but I will b next time I'm in it. N yaeh she goes alright nothin scary but gets along ey. I'll try trimmin it on the last hole I gues. Am sarting to think it might need a taller prop to make it a bit slower out of the hole n give it more legs cause yes the boat is only small n very light and wonder if this might cause it to free spin the prop too easy. That or is there anyway the prop can slip on its spline or what ever its attached to. I cant get it to slip though when motor is off, in gear n turning it over by the prop by hand it just winds the motor over. I actually expected it to get up n go alot more than it does n that tends to make me think its under propped. Thoughts?

[STUIE63]

have a talk to solas they might have recomendations on props to suit your hull and motor my guess would be more cup for better grip in the water .whatever you do please make sure your motor can reach max revs at WOT
Stuie

[D river]

have a talk to solas they might have recomendations on props to suit your hull and motor my guess would be more cup for better grip in the water .whatever you do please make sure your motor can reach max revs at WOT
Stuie

Sorry mate never heard of solas where abouts are they?

[Willo]

Hi D river
Around the mid to late 90's I had a 25HP Mariner and also had the same cavitation problems you speak about
Ended up discussing it with a Propeller guy at one of the Boat shows (think it might of been Solas) and was told that Mariner uses the Mercury gear box lower leg and it was a Known design fault in the leg that cause the cavitation.and notthing much could be done about it . He suggested that I get the Propeller cupped ,which I did and it did help a little .
Anyway sold the motor , put a yammie 25 on and no cavitation problem on the same boat.???
Willo