Cavitation Talk

« **Reply #25 on:** March 02, 2016, 09:34:21 AM »

The more i think about this the more things i start to remember

When i first built the jet/boat and would launch it it would pull past the max rpm but not by much. Maybe 4-500 rpm then load up and come down. I did blend the intake in when i first put the boat together but only used regular body filler.

Then one trip out to the avi, i took a rather spirited turn and the boat caivtated really badly. The only thing i noticed different per say after this spirited turn, was my filler was gone and the bad entry is back. The cavitation issue started shortly after, probably at the same time. I cant be sure because it went on the trailer immediately afterwards.

Couple of trains of though here...

1. The entry to the intake being blended was helping, and that's why it wasn't so bad
2. Now that the engine is making good power and running correctly i'm just blowing through it and cavitating from the other reasons mentioned in this thread.

Just a little more information to share.

« **Reply #26 on:** March 02, 2016, 09:35:10 AM »

Quote from: GT Jets on March 02, 2016, 09:19:37 AM

Ride plate should be a negative. (Up from keel line) in other words it would read -3.75°. It should not be down from the keel line, especially with a back cut shoe.

Do you have a bowl blead?

GT

Yes thats what i mean, it would be a negative angle.

And no bowl blead

« **Reply #27 on:** March 02, 2016, 10:54:02 AM »

The more I think about this, the more I feel you have a funky intake install.

Do you have any pictures of the intake from the bottom?

« **Reply #28 on:** March 02, 2016, 11:05:31 AM »

Quote from: GT Jets on March 02, 2016, 10:54:02 AM

The more I think about this, the more I feel you have a funky intake install.

Do you have any pictures of the intake from the bottom?

Thats what im thinking too. Unfortunately i dont have any pictures.

i can try to explain it

Flat intake in a rounded keel.

The intkae is approx 1/2-3/4" above the keel, and then needs to be blended in.

« **Reply #29 on:** March 02, 2016, 11:23:34 AM »

Quote from: steves86ta on March 02, 2016, 11:05:31 AM

Thats what im thinking too. Unfortunately i dont have any pictures.

i can try to explain it

Flat intake in a rounded keel.

The intkae is approx 1/2-3/4" above the keel, and then needs to be blended in.

This would put the intake too high in the hull.

Without a spoon before the opening it will never really work right. IMO anyway.

Has it been set back? I thought I read it was.

GT

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« **Reply #30 on:** March 02, 2016, 12:06:43 PM »

Quote from: GT Jets on March 02, 2016, 11:23:34 AM

This would put the intake too high in the hull.

Without a spoon before the opening it will never really work right. IMO anyway.

Has it been set back? I thought I read it was.

GT

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I might be over estimating that, it may only be that 1/2"-3/4" because they took a flat intake and ground it round kinda? Its hard to explain. But the shop that did this work IMO did a pretty shotty job.

MY pump is in the stock location for the Roger's. Its what some call a half set back. The hand hole is about halfway out.

« **Reply #31 on:** March 04, 2016, 09:47:13 AM »

Thoughts on adding a Stuffer?

« **Reply #32 on:** March 04, 2016, 09:54:02 AM »

Quote from: steves86ta on March 04, 2016, 09:47:13 AM

Thoughts on adding a Stuffer?

Yes...

Dan'l

« **Reply #33 on:** March 04, 2016, 12:26:13 PM »

Are all stuffers the same? Special order?

« **Reply #34 on:** March 04, 2016, 01:03:12 PM »

Mine is custom built, but its a WJ.
with your fab skills, should be easy to build one, I'm planning on building one for my Dom bowl, but has an AT impeller in it...I think thats a mis-match, IDK

Dan'l

« **Reply #35 on:** March 10, 2016, 02:44:47 PM »

So, since i dont have it here, and its bugging me not knowing what may be going on with it. I keep reading to learn as much as possible

I stumbled across a "spoon" thread on another site. Simple theory that makes sense to me, but ive never dug into it

One of the replies was this video called the Coanda effect.

Knowing how the bottom of my boat looked before i re-blended everything in. And after watching this video a couple of times. I think that the bottom may have been creating this effect but with the spoon turned around opposite of waht you want. Example Starting at 2:12 in the video.

I can totally see this happening in my case, because of how the intake/keel was not blended. Obivously its just a theory, but good information to have anyway. Though, i do think this would be a bigger problem at speed.

But my shoe/loader could be grabbing the water at speed

Anyways, heres the video

« **Reply #36 on:** March 13, 2016, 07:59:45 AM »

I went and picked the boat up Friday night. Brought it home and pulled it apart. Just to double check everything. My clearances are not the greatest

Impeller to suction housing is .175

Impeller wear ring shoulder to wear ring is .145

impeller to bowl is .170

axial clearance is .024

I also finished blending the intake in and now it looks great. After watching the coanda theory video I think that wad playing a huge part. think in going to tighten the pump up a bit and bring the clearances closer as well as build a stuffer for it.

I was thinking cutting the impeller about .110.

That would give me

.065 impeller to suction housing
.035 wear ring shoulder
and making a .230 stuffer

sounds okay to me what do you think?

« **Reply #37 on:** March 13, 2016, 09:33:09 AM »

Quote from: steves86ta on March 13, 2016, 07:59:45 AM

I was thinking cutting the impeller about .110.

That would give me

.065 impeller to suction housing
.035 wear ring shoulder
and making a .230 stuffer

sounds okay to me what do you think?

Don't cut the impeller, then you will end up with some random bastard shtuff.

The shoulder on the impeller and the installed height of the wear ring should be 1.063. That way, the clearance between the impeller and suction housing will be the same as the impeller to were ring rear surface, front and back. Cut/shim the face of the shaft to achieve .035 front/rear clearance to the wear ring/suction housing and impeller. If you are concerned about sucking up sand, you can open that clearance to .055.

The tighter everything is, the harder it will hit.

« **Reply #38 on:** March 13, 2016, 09:36:40 AM »

Steve-

If I remember right, when I put my pump together,

Impeller skirt to wear ring shoulder- .017"
Impeller axial radius- .011" (per side, .022" total)

This was an American Turbine AA, aluminum impeller, with the stainless shouldered wear ring, in a Berkeley JC pump.

When I pulled it apart, wear ring to impeller skirt was at .047" (feeler gauge)
and axial radius was at .090"/side, .180" total. (Berk A2 impeller)

Hope this helps

Dan'l

« **Reply #39 on:** March 13, 2016, 08:06:54 PM »

Thank you very much Joe.

I understand what you are saying about cutting the shaft and not the impeller so that everything will interchange if needed.

But at this current time I don't have the time, resources, or place to pull my engine out to get the shaft out.

Since the plan is to save up and buy a stainless impeller than having the pump built and detailed I'll have everything set then.

I decided to cut the impeller this time and bring my clearances as close to. 035 as possible.

Big thank you to Lee (69kona) for helping me turn the impeller.

I'll get her installed tomorrow to check everything one last time

Daniel,
Thank you for the info. That helps out. Those clearances sound very tight to me. You didn't have issues with sand?

« **Reply #40 on:** March 13, 2016, 08:24:11 PM »

No issues with sand.

If I remember right, Berk specs were .012"/side or .024" total and .020" front to rear.
Without shims, I was at .017", smallest shim I had was .010", and .027" seemed counter-intuitive (frt to rear).

Dan'l

« **Reply #41 on:** March 14, 2016, 06:33:17 AM »

Anytime 👍

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« **Reply #42 on:** March 14, 2016, 09:42:06 AM »

Quote from: mash on it on March 13, 2016, 08:24:11 PM

No issues with sand.

If I remember right, Berk specs were .012"/side or .024" total and .020" front to rear.
Without shims, I was at .017", smallest shim I had was .010", and .027" seemed counter-intuitive (frt to rear).

Dan'l

I read (cant find it now, go figure) but i read that the factory berk specs were closer to the .125 range than smaller. the only thing realitively tight was the Axial and that was .030 if i remember correctly

Ill try to find the link again.

But regardless. I should now be set right at .030 front/rear. And will be making the stuffer this weekend

« **Reply #43 on:** March 14, 2016, 12:48:12 PM »

Found the specs too, From A/T:

The clearance between the impeller
and wear ring is .012 per
side, .024 total. As the impeller
and wear ring wear this clearance
increases. Measure the Impeller
to fit with an undersized wear
ring. By doing this you can
bring the clearance back to the
original setting. Stock measurement
is 7.220 to 7.225

American Turbine spec is .030", f to r, Never could find Berk specs, I thought it was .025" GT would know

from AT, On Berk pumps-

Looking in the inspection hole check the axial clearance between
the impeller and the wear ring shoulder. Clearance should be between
.025 and .035.

I guess I built my pump in march of 13, not march of 14, and was .023"/side or .056 total, not .180" total...CRS

http://www.socaljetboats.com/jet-pumps/berk-pump-specs/msg193851/#msg193851

Dan'l

« **Reply #44 on:** March 14, 2016, 12:53:04 PM »

Quote from: mash on it on March 14, 2016, 12:48:12 PM

Found the specs too, From A/T:

The clearance between the impeller
and wear ring is .012 per
side, .024 total. As the impeller
and wear ring wear this clearance
increases. Measure the Impeller
to fit with an undersized wear
ring. By doing this you can
bring the clearance back to the
original setting. Stock measurement
is 7.220 to 7.225

American Turbine spec is .030", f to r, Never could find Berk specs, I thought it was .025" GT would know

from AT, On Berk pumps-

Looking in the inspection hole check the axial clearance between
the impeller and the wear ring shoulder. Clearance should be between
.025 and .035.

I guess I built my pump in march of 13, not march of 14, and was .023"/side or .056 total, not .180" total...CRS

http://www.socaljetboats.com/jet-pumps/berk-pump-specs/msg193851/#msg193851

Dan'l

Ah i see now, Yes thats what i mean by Axial. The Axial clearance ( i could easily be using the wrong term) is between 25-35. Thats total between the wear ring and the impeller.

The front/Back clearance is in these pictures below. Keep in mind, i am not running a shouldered wear ring anymore. So the suction housing is basically the shoulder

Front of impeller to suction housing comes from this edge (where the playdoh is)

Wear ring shoulder to wear ring comes from here (again, playdoh)

And then impeller to bowl

« **Reply #45 on:** March 14, 2016, 12:56:23 PM »

Axial=parallel with shaft
Radial =outward from shaft rotation.

GT

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« **Reply #46 on:** March 14, 2016, 12:57:21 PM »

Quote from: GT Jets on March 14, 2016, 12:56:23 PM

Axial=parallel with shaft
Radial =outward from shaft rotation.

GT

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So see... i am a retard using the wrong term lol

« **Reply #47 on:** March 14, 2016, 12:57:56 PM »

Quote from: steves86ta on March 14, 2016, 12:57:21 PM

So see... i am a retard using the wrong term lol

Not any more. ...

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« **Reply #48 on:** March 14, 2016, 01:02:50 PM »

Quote from: GT Jets on March 14, 2016, 12:57:56 PM

Not any more. ...

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This is kind of why i made this thread. I know i cant be the only person that has ever come across an issue similar to this. I'd rather share my information and what may improve/does not improve in the hopes that it'll help others later.

Same thing when it comes to the terms...

I have a pretty good feeling about the improvements i have made. Ill know in 2 weeks if they worked.

But im betting going from the massive amount of clearance i had to a .030 or so. Along with blending the intake in and cleaning the entire entry way up into the intake. Im expecting some decent improvements.

One question for you all...

I took a file, and knife edged my loader. Bad idea, good idea, doesnt matter?

I also went ahead and cleaned up my impeller and sharpened them too.

« **Reply #49 on:** March 14, 2016, 01:07:19 PM »

Nothing you will be able to notice, most folks feather the wrong side though. Which ultimately can hurt performance.

GT

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