Jet jon cavitation issues

[PSG-1]

Not a problem, glad to be of assistance. Keep us posted on what you find out.

 

[willholl79]

I found this grate on ebay that should fit. I wonder if it will be an improvement over stock?

[URL=https://s247.photobucket.com/u...EE-kN7fOBP8Y0VeZyw60_57_zps65b5b3b7.jpg[/img][/url]

 

[PSG-1]

Perhaps so, because it has fewer tines, and the angle of the blade is probably more aggressive than a stock grate. You could also make a piece of plate and put it about halfway, then weld it at a forward-facing angle. Pump components such as grates, etc are cast aluminum, and generally weld without difficulty, so, they're easy to modify.

 

[willholl79]

I'm going to try that grate and may add to it depending on results.

I took the intake grate off to check the impeller and wear ring. It looked suprisingly good. Some very minor pitting on the impeller blades but no nicks or gashes. Wear ring shows no scoring. I didn't have a feeler guage on hand(my tools are still packed up form moving 2 months ago) but it looked tight. I was kind of dissappointed that it wasn't trashed and the main problem.

If it's not sucking air through the intake grate, then it's got to be "pushing out"because of the nozzle being too shallow.

The first and only tme I've had it in the water it ran better with just me in the back as opposed to 2 people in the back. We had it weighted down to the point water was flowing over the transom when decelarating.

Even with just me on the back and on plane, it didn't run level like a jet boat should. The previous owner has it set up to drive from the rear, but to run level on plane the driver needs to set over the motor.

 

[PSG-1]

If it's not sucking air through the intake grate, then it's got to be "pushing out"because of the nozzle being too shallow.

The first and only tme I've had it in the water it ran better with just me in the back as opposed to 2 people in the back. We had it weighted down to the point water was flowing over the transom when decelarating.

Even with just me on the back and on plane, it didn't run level like a jet boat should. The previous owner has it set up to drive from the rear, but to run level on plane the driver needs to set over the motor.

Based on that, it could be that there's actually too much weight on the stern, which could put the forward edge of your intake scoop near the aerated water being created as your boat moves along slowly before you try planing off. Then when you try to plane off, it sucks all that aerated water and causes it to cavitate.

Maybe try shifting some weight forward and see if that changes it. This should put more of the hull in contact with the water, and hopefully give the water running along your keel enough distance to smooth out before hitting the pump intake.

Top loader grate will also help with this, as well.

 

[RivrLivn]

I'm definitely no jet-jon expert, but from the pic the whole bottom of the boat especially the transition from one hull to the other in front of the intake looks extremely rough. I know my boat has a very smooth delta pad that runs 8 feet out to create a smooth feed to the intake. I have heard of people just having a small dent in front of the intake causing performance issues.

Just a thought. Looks like a fun little project when you get it running good.

 

[PSG-1]

You may be right about that, RivrLivn. Good call.

From the photo, it's hard to tell if the strakes are on either side of the intake scoop, or if they're right on the edges. If they're too close to the edges, it would indeed cause a massive air pocket, and cavitation. Hard to tell without being there to see it in person and lay a straight edge on those strakes to see if they miss the intake area.

 

[willholl79]

You are right Rivrlivn, the transition leaves a lot to be desired. It is definitely on the list of things to address.

I'm going to try a few things to try to make it run better, without putting tons of time and money into it, not knowing if it will do what I need; taking 2 people and gear up and down the river.

According to my research, the WR500 Waverunner weighs in the neighborhood of 400Lbs.
A Sylvan 1436 weighs 175Lbs empty. Take the motor/pump at a guesstimated 200Lbs and add it to the the jon you get 375Lbs. I understand you have to account for the more surface area on the flat bottom jon and such, but hillbilly math says the 500cc(with oversized pistons and carb) should haul a couple people up and down the river assuming it's not "sucking air" through the grate or "blowing out" the back.

 

[willholl79]

PSG-1 » 12 Jun 2013, 18:40[/url]"]You may be right about that, RivrLivn. Good call.

From the photo, it's hard to tell if the strakes are on either side of the intake scoop, or if they're right on the edges. If they're too close to the edges, it would indeed cause a massive air pocket, and cavitation. Hard to tell without being there to see it in person and lay a straight edge on those strakes to see if they miss the intake area.

The strakes are just to the edge of the intake, maybe an inch or so outside of either side.(the grate is not in)

[URL=https://s247.photobucket.com/u...IMG_20130612_192329_874_zpscbd881d1.jpg[/img][/url]

 

[PSG-1]

That's a better angle on that photo.

Looking at it, I can clearly see the strakes are definitely to the sides. I wouldn't think that would cause problems, but then again, I may be wrong.

 

[willholl79]

Update: The used pro-tech intake grate got here yesterday and I put it on this morning, put the livewell plug in so that nothing was sticking below the hull and put it in the water. Much, much, better! Not perfect, but it's improving. It now planes and runs WOT with 2 people. It likes smooth water, the least little chop and it hesitates a little, but I think I can work that out.

 

[PSG-1]

Glad to hear it's working a little better. As for cavitation in chop, no way to completely get rid of that problem.

I just got back from the Santee Delta today. The tide was falling, and the wind blowing from an easterly direction, so, there were a few places it was choppy and I simply had to back it down and go slow. My boat likes flat water, but if I start getting in chop 1/2-1 ft in height, it starts cavitating like crazy. But even an actual jetboat will have this problem. I know, because I used to own a 14 ft Sea Doo Speedster, it didn't like chop, either.

 

[willholl79]

When I had the boat in the water this morning, it ran decent in smooth water; almost glass. The slightest ripple from the wind would cause some cavitation.

Edit: This was with me, my wife, and 3 year old son in the boat. I didn't get a chance to run solo.

 

[willholl79]

My next question: If I were to upgrade the prop, what pitch would give me a little more low end(plane quicker), and not kill the top speed?

 

[PSG-1]

Now THAT is a difficult question. :? What pitch is the impeller you're using?

In my boat, I'm running a 13/19 pitch. Also had good results with a 14.5/17 pitch

Unlike a boat prop, which is the same pitch, jet boat impellers are progressive pitch, meaning the leading edge has a steeper pitch to pull the water in quickly, this is where the hole shot comes from....and then changing to a higher final pitch at the trailing edge, where the top end is generated.

Lower pitch can handle aeration/cavitation better than higher pitch. In your case, I'm thinking a 13/19, or maybe even a 12/18 would have better hookup in chop, without losing much top end.

Impros can re-pitch your prop to whatever pitch you want. Check out their website, they have a good bit of info about props.

 

[willholl79]

PSG-1 » 17 Jun 2013, 17:28[/url]"]Now THAT is a difficult question. :? What pitch is the impeller you're using?

In my boat, I'm running a 13/19 pitch. Also had good results with a 14.5/17 pitch

Unlike a boat prop, which is the same pitch, jet boat impellers are progressive pitch, meaning the leading edge has a steeper pitch to pull the water in quickly, this is where the hole shot comes from....and then changing to a higher final pitch at the trailing edge, where the top end is generated.

Lower pitch can handle aeration/cavitation better than higher pitch. In your case, I'm thinking a 13/19, or maybe even a 12/18 would have better hookup in chop, without losing much top end.

Impros can re-pitch your prop to whatever pitch you want. Check out their website, they have a good bit of info about props.

The stock impeller for a WR500 is an aluminum 16 pitch(average of 15/17????), according to the interwebs. When I looked at the impeller through the intake grate, it is aluminum, I assume OEM.

 

[PSG-1]

If it's aluminum, it's definitely stock!

And you should definitely replace it with a stainless impeller. A swirl-type, such as a solas concord, or a skat-trak, would probably make a noticeable difference in the overall performance.

If your prop is a 15/17 pitch, you'd probably have the best results by stepping down to a 13/19. It will give a little more top end (maybe .5 - 1MPH) but the lower pitch of the leading edge should give it a better bite in the water, and reduce the cavitation.

Here's some tech info, as well as a link to Impros:

https://impros.com/store/index.php/tech-info/tech-q-a.html

 

[willholl79]

Solas stocks a 13/18 and a 14/18. I'm thinking 13/18 due to weight.

 

[PSG-1]

13/18 would probably be best, due to weight and the existing problems with cavitation.

Reading through the tech info, it says that aluminum impellers use a larger hub, which does not allow as much water to flow through the pump as using a smaller hub, like they do with stainless.

Also, while you have the pump apart, check your stator vanes for chips, nicks, etc. If the vanes are damaged, that can also cause cavitation.

 

[willholl79]

Ordering the 13/18. We'll see what happens!