242 limited pump questions.

[swatski]

I actually think your impeller and wear ring is in very good shape. From what I see.

 

[Utley]

Just for my comparison, how much throttle does it take someone with a similar boat to pull a wake boarder out of the water? 140 lb rider with two adults and a child in the boat. It takes me full throttle til it revs out, then I have to back off and get back into the throttle again to keep the speed up enough for them to stay on top of the water and for the boat to eventually plane out. Seems to take along time for the boat to finally plane out.

 

[swatski]

Just for my comparison, how much throttle does it take someone with a similar boat to pull a wake boarder out of the water? 140 lb rider with two adults and a child in the boat. It takes me full throttle til it revs out, then I have to back off and get back into the throttle again to keep the speed up enough for them to stay on top of the water and for the boat to eventually plane out. Seems to take along time for the boat to finally plane out.

Sorry, don't have the same boat, but that is ridiculous - you are certainly sucking air - cavitation can also be caused by air leaks in the pump transom plate.

 

[Bruce]

Just for my comparison, how much throttle does it take someone with a similar boat to pull a wake boarder out of the water? 140 lb rider with two adults and a child in the boat. It takes me full throttle til it revs out

I would not want to go full throttle on my 230, would rip their arms off.

The Boattest page I linked to has a RPM vs speed chart that is very useful for comparison.

 

[Utley]

Ok, so I think I'm gonna replace the worn transom plate in the pump. Also maybe the impeller, and the impeller duct? Not sure if that is the right term or not, the part that holds the shaft bearings with the fins on it. What are your guys' thoughts on that impeller duct? The fins on the housing are all corroded, wondering if that will affect the water flow after the pump, or if it's not a big deal. From the looks of the impeller ring, it looks in good shape, and don't see a reason to replace that. Was only thinking the impeller because it is right at the limit for allowable clearance.

 

[Bruce]

Ducts and bearings are some of the less expensive parts so I would change them.

This post may help https://jetboaters.net/threads/changing-yamaha-jet-boat-pump-duct-housing-bearings-and-switching-to-oil-bath-lubrication.10155/

 

[swatski]

Ok, so I think I'm gonna replace the worn transom plate in the pump. Also maybe the impeller, and the impeller duct? Not sure if that is the right term or not, the part that holds the shaft bearings with the fins on it. What are your guys' thoughts on that impeller duct? The fins on the housing are all corroded, wondering if that will affect the water flow after the pump, or if it's not a big deal. From the looks of the impeller ring, it looks in good shape, and don't see a reason to replace that. Was only thinking the impeller because it is right at the limit for allowable clearance.

That transom plate is the least expensive part at about $100, but quite a bit of work to take it of and clean and seal everything up. The other parts are more expensive but relatively fast to change as there is really no sealant in between, except your impellers may or may not want to come off the shafts...
Not sure what to say, but I think I would start with the transom plate replacement and sealing the tunnel, and then check the performance. I would not be surprised if that alone cured most of your cavitation.
The duct (impeller duct, with the bearings) is in bad shape, no doubt, but it probably does not, per se, cause most of the cavitation, it has just been sitting on the receiving end of it. If the shaft/impeller move freely and smoothly, and do not make any noises, it may not be your biggest worry at this time.

 

[Utley]

I checked my bearings when I had the pumps apart last time, and spun free and clear. Will probably switch over to the oil bath system while I have them apart and try them the way they are. You're right, that would be an easy part to swap over when time came if there was still problems. Transom plate will be the most in depth part to do.

 

[waterboy]

@Utley I would add again, I think you need to focus on the duct part as well. That part is as critical to the rest for producing thrust out of the pump and yours is corroded very badly. It will mess up the flow out of the pump and cause cavitation.

Here is something I found on line that explains it much better than I can... "The stator has a main purpose that most may overlook; probably wondering what it’s doing in there. But the boat can’t run without it. If it were not there, the torque from the impeller(compressor) would cause the boat to twist to the right from centrifugal force. The stator has a very aggressive blade design that almost completely reverses the direction of water flow. By changing the direction of the flow, it stabilizes the water for even output, removing the centrifugal force of the impeller. But more importantly, by changing that direction, it increases the energy of the fluid movement. "

As far as the comments that it is on the downside of the impeller as doesn't matter, how is it that there are aftermarket cones out there that some folks have used on this board to improve performance of the pump??? Well the reason is that the whole flow dynamics throughout the pump matters to get proper performance. Intake grate, impeller, clearances, duct design, cone design through to exit nozzle design all add up to give you proper holeshot and top end speed. Start messing with the design of this and you impact (for better or worse) holeshot and/or top end speed.

Not trying to stir things up but would hate to see you go through a lot of work and not get the desired results.

 

[Utley]

The more I thought about it, I decided to do the impeller duct also. Might as well have everything new. Seeing your post and the explanation behind it affirmed it for me. Is there any aftermarket to look at for these parts, or go with factory Yamaha? Probably going to stick with the stock pitch on the impeller.

 

[swatski]

@Utley I would add again, I think you need to focus on the duct part as well. That part is as critical to the rest for producing thrust out of the pump and yours is corroded very badly. It will mess up the flow out of the pump and cause cavitation.

Here is something I found on line that explains it much better than I can... "The stator has a main purpose that most may overlook; probably wondering what it’s doing in there. But the boat can’t run without it. If it were not there, the torque from the impeller(compressor) would cause the boat to twist to the right from centrifugal force. The stator has a very aggressive blade design that almost completely reverses the direction of water flow. By changing the direction of the flow, it stabilizes the water for even output, removing the centrifugal force of the impeller. But more importantly, by changing that direction, it increases the energy of the fluid movement. "

As far as the comments that it is on the downside of the impeller as doesn't matter, how is it that there are aftermarket cones out there that some folks have used on this board to improve performance of the pump??? Well the reason is that the whole flow dynamics throughout the pump matters to get proper performance. Intake grate, impeller, clearances, duct design, cone design through to exit nozzle design all add up to give you proper holeshot and top end speed. Start messing with the design of this and you impact (for better or worse) holeshot and/or top end speed.

Not trying to stir things up but would hate to see you go through a lot of work and not get the desired results.

Look, no one is trying to steer the OP the wrong way, I certainly am sharing my experience and a little bit of knowledge to help. That's what we do here.
That said, not sure what makes you think the stator/duct here wouldn't do its job? And the cone issue is quite different, yet - the aftermarket varieties (such as Lucky 13) permit adjusting the volume inside the venturi. Please do now confuse these issues. And yes, you WILL benefit from blueprinting each and every part of a pump. But how much - that is a different story.

With a situation like this, I would suggest a triage method for fixing the issues. Fixing some will have a bigger effect than other.

 

[swatski]

@Utley As far as the comments that it is on the downside of the impeller as doesn't matter, how is it that there are aftermarket cones out there that some folks have used on this board to improve performance of the pump???

Incidentally, here is a thread on an aftermarket pump cone in our boats. And a pretty good read, too, if you ask me .
https://jetboaters.net/threads/anyone-tried-the-lucky-13-perfomance-adjustable-pump-cone-in-a-boat.7967/

--

 

[waterboy]

I am not suggesting anyone is trying to steer anyone wrong, please don't take it that way. We are all here to help. I am mentioning these other parts because they all have some impact on the performance of the pump. The cone discussion was a very interesting read too.

I only bring up the stator since the impeller was reported to be in decent shape and the clearance of the impeller is good. With my background dealing with pumps in the industrial world (not jet ski pumps), I know that the stator is probably the next most critical element in the a pump, assuming everything is sealed up real well to prevent cavitation. I am just not wanting the OP to overlook this part. The pictures were hard to see exactly but heck it looks like there is 1/4" of metal missing.

 

[Bruce]

@waterboy, do you think that polishing the stator or coating it with something slick would improve efficiency?

 

[swatski]

I think the general view is - adding vanes is beneficial (they go up to 12 in some of the racing pumps) but polishing the them up, or sharpening them - not so much.
Missing chunks - that would be different - and I agree with @waterboy it is hard to tell from that pic.

 

[Bruce]

I found this article interesting http://www.belzona.com/pumps/assets/pdf/en/articles/ARTICLE-WaterWorldReprint.pdf

It suggests a possible gain of 3% efficiency in a new pump and up to 8% in a rebuilt pump from using slick coatings.

This perhaps newer product suggests a potential gain of 7% for new pumps and 20% on rebuilt pumps. http://www.belzona.com/en/products/1000/1341.aspx

I have considered sand blasting the metal parts of my pump, smoothing all metal surfaces (removing high points) resealing then coating with this or a similar product.

Here is a video about the products

 

[waterboy]

I know the limits of my knowledge on pumps is more practical and in the industrial world. Relating to what we have in our pumps, and I think all would agree, the intake tunnel, impeller, stator, and exit venturi are all designed to boost pressure and velocity of the water out the exit and give us our thrust. Coatings, and other tweaks, or probably more for the person who wants to measure gains in fractions of a mph gain or holeshot, when taken all together, can add up to big gains. All that being said, I have to tap out on knowing much more than that.

 

[waterboy]

@Bruce Loved that video. The pumps they were showng me reminded me of some of the power plants I used to wander through. We dealt with pumps that were moving right at 400,000 gallons per minute or more. A lot of plants also used the Belzona products for various applications too. Very good products.

The coating stuff is cool but when they say 7% gain in efficiency. Is that in water flow, electricity usage for the pumps or what? Not sure how that would relate to mph gains in our boats???? It may not even be perceptible gains. Trying to put an industrial plant look at this when they talk about gains. I 'm not sure...

 

[swatski]

Good info @Bruce.
If you must do it... to smooth out the flow, DO not sharpen the leading edge of the veins, sharpen the trailing edge (think aeroplane wing).
LOL. It may or may not make real life difference in top speed or anything, but it will look good!

Here is where I'm coming from, not making this $hit up!
http://www.greenhulk.net/forums/showthread.php?t=92353

 

[Bruce]

Is that in water flow, electricity usage for the pumps or what?

I believe it is a decrease in electricity consumption but they also mention that the pumps now have a greater capacity.

A 10% increase in efficiency is not going to cause a 10% increase in speed. But it should provide some increase in speed and a greater increase in fuel efficiency. Assuming that I can get my hands on the stuff it seems like a reasonable alternative to powder coating my jets.