Here's the situation. I have a 33' Wellcraft Martinique with twin 454 Horizon inboards. When the boat first goes on plane, the port side wheel cavitates briefly. Then at around 3600 rpm's it'll cavitate again. The props are 4 blade nibal that were just repitched (wot was too low) and polished. Any ideas?
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Cavitation
- Thread starter The_Mayor
- Start date
You wouldn't think a newly repitched prop would have and burrs or other issues. Has anything else been done to your hull? Is it clean? Could be something on the hull introducing air somewhere forward of the porp, ventilating it.
after you go swimming to see for yourself there's no debris of any kind on the wheels,
find out from the prop report what pitch, diameter & cup was on the wheels when it lef the shop and then go back to wellcraft and find out what wheel dimensions & cup the boat was fitted with originally. if they dont match, then the cavitation issue is somewhere else in the drive line.
find out from the prop report what pitch, diameter & cup was on the wheels when it lef the shop and then go back to wellcraft and find out what wheel dimensions & cup the boat was fitted with originally. if they dont match, then the cavitation issue is somewhere else in the drive line.
What is attainable WOT now compared to the spec WOT range? Are you reaching near the high end or just can't get past 3600RPM ? Repitching is usually up to 2" max from the original specs since they can't change the root, so it's possible you really need another set of even lower pitched props. You did have them LOWER the pitch , not raise it , and confirmed results, correct? Just checking....
Is there possibly a T/D sticking out ahead of the cavitating prop?
Are you making good use of tabs to reduce the prop load as well as reduce chance of entrained-air flow past the props?
Hopefully you had the prop work done at a PropScan or MRI shop so, as Vic mentions above, you have a before and after scan printout confirming intial condition, work done and present condition to least ISO 1 spec., and can also see the props were matched ( final average pitch , dia, #cup).
It's always possible the prop was damaged after service/ before it was installed on the boat -happens all to easily. Few yard techs are going to reveal they dropped the prop and the change could be unnoticeable by quick visual check. You never know...
Also, just because they were just serviced doesn't mean they couldn't have grounded or hit flotsam on the maiden run.
Is there possibly a T/D sticking out ahead of the cavitating prop?
Are you making good use of tabs to reduce the prop load as well as reduce chance of entrained-air flow past the props?
Hopefully you had the prop work done at a PropScan or MRI shop so, as Vic mentions above, you have a before and after scan printout confirming intial condition, work done and present condition to least ISO 1 spec., and can also see the props were matched ( final average pitch , dia, #cup).
It's always possible the prop was damaged after service/ before it was installed on the boat -happens all to easily. Few yard techs are going to reveal they dropped the prop and the change could be unnoticeable by quick visual check. You never know...
Also, just because they were just serviced doesn't mean they couldn't have grounded or hit flotsam on the maiden run.
Since you presumable reduced pitch this is a real surprise. how do you know it is cavitating and not the trans slipping??
A cause could be prop improperly seated on the shaft taper because the key was too far forward.
A cause could be prop improperly seated on the shaft taper because the key was too far forward.
Okay, I went out on the boat today and dove down to look at the props. They both are spotless with no marks anywhere.
I was only able to reach 4400 rpms last year. After work was done, i can get up to 4800 rpms which is mfg suggested wot. So i think i'm good there.
I thought about trans slip, but wouldnt that happen under a load? The cavitation happens after the boat is planing.
I think i'm using the tabs correctly. They're down as i come up on plane. As soon as i'm on plane, I put them all the way up.
I was only able to reach 4400 rpms last year. After work was done, i can get up to 4800 rpms which is mfg suggested wot. So i think i'm good there.
I thought about trans slip, but wouldnt that happen under a load? The cavitation happens after the boat is planing.
I think i'm using the tabs correctly. They're down as i come up on plane. As soon as i'm on plane, I put them all the way up.
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Not an expert, but if the props and power train is all okay, is there a rough spot or junk stuck to a thru hull sending air bubbles back to the prop at certain speeds. (?)
- Joined
- Jan 4, 2008
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Could be that the lower pitch props are now biting more
water, hence demanding more torque from the drivetrain
and causing some slippage from that transmission.
H
water, hence demanding more torque from the drivetrain
and causing some slippage from that transmission.
H
Took pitch out of the props. Higher revs at wot. Less torque from the drivetrain. Besides, the cavitation is happening when the boat is just on plane, not while it's on its way up. My thought is that there is steps in the hull just aft of midship. When they break the waters surface could air be forced in front of the blades?
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- Mar 4, 2001
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That would be "ventilation" not "cavitation". The correct name may be important since the corrective measures would be different.
Is the boat's acceleration more lively? You might be correct about grabbing some air off a step.
Is the boat's acceleration more lively? You might be correct about grabbing some air off a step.
"I think i'm using the tabs correctly. They're down as i come up on plane. As soon as i'm on plane, I put them all the way up."
Your statement is incorrect for most boats using trim tabs. Do not put them all the way up when finally on plane. Find a happy medium when the boat is on plane, no plowing or bow up and you can achieve almost maximum speed.
Your statement is incorrect for most boats using trim tabs. Do not put them all the way up when finally on plane. Find a happy medium when the boat is on plane, no plowing or bow up and you can achieve almost maximum speed.
quote:
Originally posted by mabbott
"I think i'm using the tabs correctly. They're down as i come up on plane. As soon as i'm on plane, I put them all the way up."
Your statement is incorrect for most boats using trim tabs. Do not put them all the way up when finally on plane. Find a happy medium when the boat is on plane, no plowing or bow up and you can achieve almost maximum speed.
I put them all the way up when on plane because the boat is going over 35mph. At 30mph I have the starboard tab down slightly to keep the boat level. I'm 280lbs, and when alone the boat leans slightly to starboard. My last boat needed som tabs to keep the bow down. This one really doesn't.
quote:
Originally posted by rbmitchell
That would be "ventilation" not "cavitation". The correct name may be important since the corrective measures would be different.
Is the boat's acceleration more lively? You might be correct about grabbing some air off a step.
Does not seem to lively when it "ventilates or cavitates". The rpm's climb 2 or 300 when it happens, but no burst of speed.
Try ignoring it for the 75 days left of this summer.
My boat needed lots of tabs and maybe at 3600 your boat angle is just so that your catching air, try more tabs and dont stay at 3600, you should cruise at 3300 if your boat will stay up at that RPM
Are you injected of 4bbl carbed? If your carbed it could be secondarys popping open to much on one side.
they get confused when they are at the edge of just opening.
they like to be really open or really shut.
Inbetween is where most people are having problems with one engine compaired to another.
My boat needed lots of tabs and maybe at 3600 your boat angle is just so that your catching air, try more tabs and dont stay at 3600, you should cruise at 3300 if your boat will stay up at that RPM
Are you injected of 4bbl carbed? If your carbed it could be secondarys popping open to much on one side.
they get confused when they are at the edge of just opening.
they like to be really open or really shut.
Inbetween is where most people are having problems with one engine compaired to another.
I'm injected. The boats sweet spot seems to be 3200rpm's at 31.5mph. I hear ya about the 75 days. If i'm paying attention, i can go from idle to wot without it cavitating. But once and a while it sneaks up on me and scares the crap out of me.
That would be "ventilation" not "cavitation". The correct name may be important since the corrective measures would be different.
I aggree,sounds like you are looking in the wrong area. If you do some research on ventalation, I think you will locate your solution. MO
I aggree,sounds like you are looking in the wrong area. If you do some research on ventalation, I think you will locate your solution. MO