Cavitation Help Needed

[Steve73]

2018 AR190 has issues getting through 7mph-17mph range. It will go through but I have to be gentle on the throttle otherwise it gives a sound pitch change that sounds like air in the jet and feels like I’m spinning my wheels. I believe this is the symptoms of cavitation right? More weight on board slower I have to go. Had 6 adults on board and I could barely get through it to get on plane. Took a good full minute or two of ever so slowly increasing the throttle through 7mph to 17mph. Eventually got on plane. Here’s a bunch of pictures. Anyone see anything that needs caulked or any issues with my impeller? I also find water has been getting in the bilge area when I spend time at speed on plane. Not sure if related. I think it’s water getting past the clean out plug but going to use a go pro next time out to figure that out.
Thanks in advance.

 

[sunbyrned]

Have you pulled the impeller out completely? Sometimes that helps to make sure everything is cleared out. I had exactly what you’re experiencing. I couldn’t see anything but pulled the impellers anyway. Still didn’t see anything but put her back together and it ran great. Maybe something fell out and I didn’t notice. Worth a try. It’s easy to do if you haven’t done it before.

 

[tdonoughue]

Doesn't look like you have any sealant left between the black intake parts and the white hull... That could do it. Impellers don't look too bad from here, but @sunbyrned is exactly right. Pull those pumps to get a good look at the impellers, the water path and all. Fill and smooth all gaps along the intake. In fact, from the factory mine had silicone in all of those bolt recesses outside the intake, as well (which shouldn't affect cavitation, but will decrease drag). Basically you need to make that path as smooth as possible. Any gap will increase cavitation. Then on the impellers, file down any small gashes in the impellers. Don't go overboard--you don't want to change the balance, just take out the burrs and nicks.

Then put it all back together and see if it sings.

 

[Steve73]

I haven’t pulled the impeller. Was hoping not necessary. I did notice the lack of caulk between the black intake grate and the white fiberglass. What kind of sealant do you suggest I apply here?

Also - are you saying the factory caulked over the screw bolts? That is an interesting idea to prevent drag.

 

[sunbyrned]

I would encourage you giving it a try. Once you learn how do it, it’s about a 15 minute procedure.

 

[2kwik4u]

Impeller looks good.
I don't see big gaps on the wear ring to the impeller. I think you're good there.

Definitely need to seal up that tunnel. This spot in particular looks bad. I bet you're pulling air through there and it's destroying the flow over the impeller.


Here's where I sealed mine: https://jetboaters.net/threads/hero-or-zero-resealed-my-jet-pump.17845/ <--others have done much cleaner jobs. There was a thread just a day or two ago where the owner had done a REALLY nice and smooth job sealing up the tunnel. Flow smoothness isn't as important as air tightness. You don't want the low pressure side of the pump to be able to "suck air" into the water stream into the impeller.

For reference, with the L13 cone, and sealed tunnel I can hammer down in my '17 AR190 with 8 adults and get zero cavitation. It might take a bit to plane at that load, but it hooks up and moves forward. Zero regard for cavitation. With just 2 adults and 2 kids in the boat, it'll pull the rope from a skiers hands if I'm not gentle with it. I boat 99% in fresh relatively clean water, and haven't had the pump apart on mine since I bought it new.

 

[Steve73]

Impeller looks good.
I don't see big gaps on the wear ring to the impeller. I think you're good there.

Definitely need to seal up that tunnel. This spot in particular looks bad. I bet you're pulling air through there and it's destroying the flow over the impeller.
View attachment 182515

Here's where I sealed mine: https://jetboaters.net/threads/hero-or-zero-resealed-my-jet-pump.17845/ <--others have done much cleaner jobs. There was a thread just a day or two ago where the owner had done a REALLY nice and smooth job sealing up the tunnel. Flow smoothness isn't as important as air tightness. You don't want the low pressure side of the pump to be able to "suck air" into the water stream into the impeller.

For reference, with the L13 cone, and sealed tunnel I can hammer down in my '17 AR190 with 8 adults and get zero cavitation. It might take a bit to plane at that load, but it hooks up and moves forward. Zero regard for cavitation. With just 2 adults and 2 kids in the boat, it'll pull the rope from a skiers hands if I'm not gentle with it. I boat 99% in fresh relatively clean water, and haven't had the pump apart on mine since I bought it new.

Thanks, This is really helpful. What do you suggest I use for sealing it up? 3M 4200? I will start with sealing it up and see if I get better performance, then maybe I will look into that L13 cone.

 

[2kwik4u]

Thanks, This is really helpful. What do you suggest I use for sealing it up? 3M 4200? I will start with sealing it up and see if I get better performance, then maybe I will look into that L13 cone.

Definitely seal it up first. It made as much or more difference than the L13 did, nad it's relatively easy and inexpensive.

I used that Loctite Marine Sealant stuff. it's held up well since '18. Was under there the other day and it's mostly still there. I think 4200 would be a good choice as well.

 

[tdonoughue]

Yes, 4200 or similar (which would be the Loctite). I would avoid just simple silicone caulk--that is what the factory uses (and that has been proven to fall out).