Cavitation

[Patricko315]

New owner of a 24 Yamaha Ar250 with 12 hours. Was on plane at 30mph and sucked up a piece of wood. Removed the wood and all was good for the rest of the day. Next outing everything running right for several throttle ups then went to throttle up and cavitation. My thought was wow not again. Checked clean plugs can’t find an obstruction. Throttled up again felt small cavitation then a slip like the obstruction passed through and all good the rest of the day. Got home and inspected from underneath and noticed the silicone is sloppy for a new boat. I’ve owned boats for 30 years but never a jet boat so trying to educate myself. I’ve read posts about intake grates needing a proper and smooth passage by the impeller housing. Attached are pictures of both sides, can somebody tell me if these are sealed properly?

 

[Dixemon]

It is not unusually to have a lot of debris in the water and have to clean it out multiple times during the day. Depending on where you boat. As an example, here on the coast of Georgia. We have a bunch of rivers that feed our tributaries, when the upper part of the state gets copious amounts of rain it washes debris towards the coast. There have been times when I have to clean small bits of Spartina grass out of the impellers all day. 95% of the time I have no issues.
To address your intakes. Yes the gaps you have pictured would do well from having some sealant. In addition to cutting away any protruding sealant that is hanging out in the water stream from the factory installation. I prefer the Sikaflex, or life Caulk, but everyone has there preference. Congrats on your new boat.

Amazon.com

 

[Patricko315]

It is not unusually to have a lot of debris in the water and have to clean it out multiple times during the day. Depending on where you boat. As an example, here on the coast of Georgia. We have a bunch of rivers that feed our tributaries, when the upper part of the state gets copious amounts of rain it washes debris towards the coast. There have been times when I have to clean small bits of Spartina grass out of the impellers all day. 95% of the time I have no issues.
To address your intakes. Yes the gaps you have pictured would do well from having some sealant. In addition to cutting away any protruding sealant that is hanging out in the water stream from the factory installation. I prefer the Sikaflex, or life Caulk, but everyone has there preference. Congrats on your new boat.

Amazon.com

Which areas need some silicone? Any other places to check for silicone?

 

[AZMark]

Anywhere that creates turbulence in the water flowing into your impeller

 

[Patricko315]

Anywhere that creates turbulence in the water flowing into your impeller

Trying to remain positive. When you go to accelerate and it makes that noise, it’s alarming.

 

[Bottom Bracket]

Trying to remain positive. When you go to accelerate and it makes that noise, it’s alarming.

Ya gotta roll into the throttle smooth, kinda like a SS side draft on a shovelhead.

I'm gonna try that sitkaflex291 stuff.

 

[AZMark]

I’m either lucky or ignorant because I’ve never noticed it on mine

 

[Patricko315]

I’m either lucky or ignorant because I’ve never noticed it on mine

When it happens you will notice. It’s an awful sound and shakes your boat.

 

[Patricko315]

Ya gotta roll into the throttle smooth, kinda like a SS side draft on a shovelhead.

I'm gonna try that sitkaflex291 stuff.

Seems like it wouldn’t matter how quickly you accelerate

 

[FSHER]

I have issues with the finish quality of my boat and my intake looks about the same. Its fine if I roll into the throttle but if I get too aggressive it will cavitate and slip without a doubt. I would imagine that this is somewhat normal(ish) being that my boat is not designed as a race boat but its my first jet boat so IDK.

I would believe that most jet boat intakes are designed best for being on a plane(?) and sort of sacrifice taking off from a dead stop. A jet engine is very similar. The engine is most efficient when air is clean, coming in straight with little to no disturbances. the intake of a jet engine is physically smooth, not a single rivet head or screw sticking out and all the gaps are sealed with a specific sealant. if a rivet or screw is sticking out and a chunk of sealant is missing you will likely create very disturbed air behind it. these will enter the compressors and if bad enough would cause a compressor stall.

below is what happens if the angle of air flow is to great. sort of similar situation where the air gets sloppy and enters the compressors and ultimately stalls the engine. when you take off on the jet boat from a stop the bow jumps up and the intake angle changes drastically and sometimes its to drastic to handle so the impeller cavitates because of a low pressure situation.



so think about all that ugly sealant and what the water is doing as it passes. it gets stuck in the gaps, gets distorted on the chunks and when it gets to the impeller, its all out of shape. rolling into the throttle slower keeps the bow down and the water coming in more clean.

at least this is what I understand

All that being said the intakes are smallish and I do think that sealing up the gaps and cleaning up the intake in general could make a drastic difference in performance. I've read and have been told that my boat should hit 43mph but I have yet to see anything higher than 39. I'm curious if cleaning up the intakes would help.

What concerns me most on my boat is that the intake duct sits about 1/4 in or more in places higher than the impeller housing. this I may have to take off and file it down.

Good Luck,

-Mark

 

[Bottom Bracket]

Seems like it wouldn’t matter how quickly you accelerate

describe noise please, metal on metal?

 

[Patricko315]

I have issues with the finish quality of my boat and my intake looks about the same. Its fine if I roll into the throttle but if I get too aggressive it will cavitate and slip without a doubt. I would imagine that this is somewhat normal(ish) being that my boat is not designed as a race boat but its my first jet boat so IDK.

I would believe that most jet boat intakes are designed best for being on a plane(?) and sort of sacrifice taking off from a dead stop. A jet engine is very similar. The engine is most efficient when air is clean, coming in straight with little to no disturbances. the intake of a jet engine is physically smooth, not a single rivet head or screw sticking out and all the gaps are sealed with a specific sealant. if a rivet or screw is sticking out and a chunk of sealant is missing you will likely create very disturbed air behind it. these will enter the compressors and if bad enough would cause a compressor stall.

below is what happens if the angle of air flow is to great. sort of similar situation where the air gets sloppy and enters the compressors and ultimately stalls the engine. when you take off on the jet boat from a stop the bow jumps up and the intake angle changes drastically and sometimes its to drastic to handle so the impeller cavitates because of a low pressure situation.

View attachment 223599

so think about all that ugly sealant and what the water is doing as it passes. it gets stuck in the gaps, gets distorted on the chunks and when it gets to the impeller, its all out of shape. rolling into the throttle slower keeps the bow down and the water coming in more clean.

at least this is what I understand

All that being said the intakes are smallish and I do think that sealing up the gaps and cleaning up the intake in general could make a drastic difference in performance. I've read and have been told that my boat should hit 43mph but I have yet to see anything higher than 39. I'm curious if cleaning up the intakes would help.

What concerns me most on my boat is that the intake duct sits about 1/4 in or more in places higher than the impeller housing. this I may have to take off and file it down.

Good Luck,

-Mark

Great explanation makes perfect sense. It’s only happened a few times will keep an eye on it. I agree with the sloppy quality sealant looks applied with no care, I expect better from Yamaha. I’ve owned several 4 stroke Yamaha snowmobiles and the fit/finish were perfect, but they were built in Japan. I also owned a Yamaha F-300 that was perfect zero issues. Guess I was expecting the same with this boat. Hopefully some tweaking and it will be good.

 

[Patricko315]

describe noise please, metal on metal?

Not metal just cavitation shaking when throttling up. I will try the gradual acceleration

 

[AZMark]

Not metal just cavitation shaking when throttling up. I will try the gradual acceleration

I honestly think you might still have a piece of garbage in your prop that you can’t see. I’ve had that happen on my boat and jet skis. It doesn’t take much with how fast these spin.

 

[Patricko315]

I honestly think you might still have a piece of garbage in your prop that you can’t see. I’ve had that happen on my boat and jet skis. It doesn’t take much with how fast these spin.

Seems like it would do it all the time. It’s sporadic since removing the big chunk. I also don’t know if it’s the same side. The last time it did it started cavitating then felt a slip like when a clutch slips, then it hooked up and no issue. Could have spit something out not sure but also felt slipping before the piece of wood.

 

[TeenGee]

I have issues with the finish quality of my boat and my intake looks about the same. Its fine if I roll into the throttle but if I get too aggressive it will cavitate and slip without a doubt. I would imagine that this is somewhat normal(ish) being that my boat is not designed as a race boat but its my first jet boat so IDK.

I would believe that most jet boat intakes are designed best for being on a plane(?) and sort of sacrifice taking off from a dead stop. A jet engine is very similar. The engine is most efficient when air is clean, coming in straight with little to no disturbances. the intake of a jet engine is physically smooth, not a single rivet head or screw sticking out and all the gaps are sealed with a specific sealant. if a rivet or screw is sticking out and a chunk of sealant is missing you will likely create very disturbed air behind it. these will enter the compressors and if bad enough would cause a compressor stall.

below is what happens if the angle of air flow is to great. sort of similar situation where the air gets sloppy and enters the compressors and ultimately stalls the engine. when you take off on the jet boat from a stop the bow jumps up and the intake angle changes drastically and sometimes its to drastic to handle so the impeller cavitates because of a low pressure situation.

View attachment 223599

so think about all that ugly sealant and what the water is doing as it passes. it gets stuck in the gaps, gets distorted on the chunks and when it gets to the impeller, its all out of shape. rolling into the throttle slower keeps the bow down and the water coming in more clean.

at least this is what I understand

All that being said the intakes are smallish and I do think that sealing up the gaps and cleaning up the intake in general could make a drastic difference in performance. I've read and have been told that my boat should hit 43mph but I have yet to see anything higher than 39. I'm curious if cleaning up the intakes would help.

What concerns me most on my boat is that the intake duct sits about 1/4 in or more in places higher than the impeller housing. this I may have to take off and file it down.

Good Luck,

-Mark

I had a 2022 210 FSH sport and never saw any GPS speed greater than 39 mph. I tried everything I could think of. Nothing helped. Got fed up. Bought a 2024 255 FSH. It hit 55mph yesterday. I'm a happy camper.

 

[Bottom Bracket]

put the throttles all the way forward and look in the nozzles.

 

[Patricko315]

put the throttles all the way forward and look in the nozzles.

What would I be looking for? It’s a sporadic thing with the cavitation or slipping? The wood chunk was obvious when traveling 35, shook the whole boat.

 

[sunbyrned]

By reading through all this, it sounds like your initial concern was solved when the piece of wood finally dislodged. It happened twice, not each time you throttled up. It doesn’t seem to me that the intake grate was a factor. It just sounds like you sucked up a stick and it dislodged and everything was good. That’s normal. You’ll get better at recognizing the sound and feel right away when it happens and there are techniques to dislodge it while on the water which you can read about in the forum. I find that I pick up stuff when I’m in wake mode or less because the boat is not pushing debris away. If I ever have to be in neutral, I just turn it off so not to suck something up then. I’m on the river with a lot of junk. When it happens again, to make sure it’s completely out, check out the pissers to see if they are both flowing good. Hope this helps.

 

[FSH 210 Sport]

From idle, just throttle up one engine to see which one has a problem. If it’s the port engine shut it off and put it in neutral, use the starboard engine in reverse to get going a bit, a few mph, then push the port throttle to wide open on the non running port engine. This will back flush the pump and remove debris that can be removed that way. Put the starboard throttle to neutral, place the port engine in neutral and Restart the port engine and test. I do this procedure first before opening the clean outs and it usually clears up what’s in there.

If you slam the throttles to wide open from a stand still you may get some cavitation even on a fully sealed up pump assembly. Not unlike the tires on your car breaking traction if you slam on the gas (got to get away before the jackers Jack) . If you roll into the throttles quickly you probably won’t get cavitation, if you do then think about sealing up all the nooks and crannies in the pump housing.