Having a ventilation/cavitation problem.

M

mwdgolf

New Member
Sep 30, 2015
20
Boston
Boat Info
1997 Sea Ray 330 Sundancer
Engines
Twin 7.4L Mercruiser w/Bravo III
I have a 1997 330 sundancer w/ twin 7.4L Mercruiser-bravo I/O. My current props are mirage 19. Just bought the boat early September. Not alot of sea time. My question is when I'm trying to get the boat to plane and a bunch of times while trying to maintain a cruise speed at around 3200-3800 rpm, the props breaks loose and over revs. Sounds like a clutch is slipping in a car. Also, the port motor seems do cavitates/ventilates more than the starboard motor. Is this normal for this boat with this engine/outdrive setup. Any input and/or advice on this problem.
 
Bt Doctur said:
B3`s are dual prop, whats the size of the other prop?
Click to expand...
I don't have dual props. Just a single, 3 blade, mirage 19 for each outdrive.

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My 270 single 7.4 came with a bravo 1 when I bought it used. I had a lot of cavitation, in turns, off the line, you name it. From a stop you pin the throttle it would go right to 4000 rpm and stay there until top speed. So I went to a four blade prop to give it more grab. This made the problem go away. Now I can really carve the wheel and not worry about washing out.
 
If they are always trimmed in then I believe KnotEasy hit the mark.

FWIW, trimmed in will cut fuel economy.
 
Sounds like you have Bravo 1's, not 3's.

If you're positive that the running conditions and/or operation of the drive trim is not causing the problem, then... it 'could' be a spun hub with your props. But that's only if you have the older style, rubber hubs. I have yet to hear of the newer style hubs "spinning" like the old ones. I would think if a new style did spin, it would immediately be completely toasted. The next thing in line after the props are your couplers. This becomes a much larger issue as the engines have to be removed to replace the couplers.

EDIT: Forgot to add...

How is your hole shot? Can you smoothly advance the throttle all the way to full without ventilating?

How is the bottom condition and drive condition in terms of growth? That can cause the issue, too. Are the props in good condition, as well?
 
Last edited:
Raytard said:
My 270 single 7.4 came with a bravo 1 when I bought it used. I had a lot of cavitation, in turns, off the line, you name it. From a stop you pin the throttle it would go right to 4000 rpm and stay there until top speed. So I went to a four blade prop to give it more grab. This made the problem go away. Now I can really carve the wheel and not worry about washing out.
Click to expand...
Thanks for the advice. I forgot to mention in my original message was that my boat would almost always cavitate/ventilate in a tight corner. Loose alot of speed.

Sent from my SM-G900P using Tapatalk
 
Lazy Daze said:
Sounds like you have Bravo 1's, not 3's.

If you're positive that the running conditions and/or operation of the drive trim is not causing the problem, then... it 'could' be a spun hub with your props. But that's only if you have the older style, rubber hubs. I have yet to hear of the newer style hubs "spinning" like the old ones. I would think if a new style did spin, it would immediately be completely toasted. The next thing in line after the props are your couplers. This becomes a much larger issue as the engines have to be removed to replace the couplers.

EDIT: Forgot to add...

How is your hole shot? Can you smoothly advance the throttle all the way to full without ventilating?

How is the bottom condition and drive condition in terms of growth? That can cause the issue, too. Are the props in good condition, as well?
Click to expand...
Thanks for the info. ....

Sent from my SM-G900P using Tapatalk
 
wondering if you have thru hull water inlets. put in the wrong place they will cause cavitation
 
330 hp with a single 19 inch pitch prop just dosent sound right.
 
Last edited:
Lazy Daze said:
Sounds like you have Bravo 1's, not 3's.

If you're positive that the running conditions and/or operation of the drive trim is not causing the problem, then... it 'could' be a spun hub with your props. But that's only if you have the older style, rubber hubs. I have yet to hear of the newer style hubs "spinning" like the old ones. I would think if a new style did spin, it would immediately be completely toasted. The next thing in line after the props are your couplers. This becomes a much larger issue as the engines have to be removed to replace the couplers.

EDIT: Forgot to add...

How is your hole shot? Can you smoothly advance the throttle all the way to full without ventilating?

How is the bottom condition and drive condition in terms of growth? That can cause the issue, too. Are the props in good condition, as well?
Click to expand...
Hole shot is not good. If I smoothly apply the throttle or get on it quick, its pretty much the same results. The "props" cavitates/ventilates.

Sent from my SM-G900P using Tapatalk
 
Bt Doctur said:
wondering if you have thru hull water inlets. put in the wrong place they will cause cavitation
Click to expand...
I'm not sure. I'll have to check

Sent from my SM-G900P using Tapatalk
 
Lazy Daze said:
How is the bottom condition and drive condition in terms of growth? That can cause the issue, too. Are the props in good condition, as well?
Click to expand...

Have you been able to check on this?
 
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