Problems with jet.

[Emiel]

Hello,

Thank you guys for having such a great fourm,

I hope you can help me with the problems with our jet boat,

It is an Ribtec boat with an inboard Mermaid /Ford Diesel engine,
with an for me unknown type of Jet, there is no kind of marking or plate on the jet.

Got the boat from internet, was an service boat for a big yacht, and only used by personel to go for grocceries, it had been out of use for approx. 10 years.
At our first test drive, the boat was not going very well, there was some force when taking off, but at speed there was no power and the engine just would rev but nothing happens besides a lot of shaking and noise.
we where not getting speeds above 10mph.

So we took the jet apart

There was a lot of space between the impeller and the wear ring, the glant seal was leaking and the bearing was gone,
so a new seal and bearing, adjusted the impeller to .30mm, and a new paint job, the inspection cover seal looks okay, but i am thinking to bond it shut, so it is airtight.

So new looking jet, new test, But the problems stays, enough force from standstill, but the top speed stays around 10-15mph, and not getting in to plane. giving more throttle just gives more revs, and noise.

It is just like the jet doesn't get enough water, and starts pumping air.

There is a grate installed, but don't have a picture at hand right now, but no ride plate.
could this be the problem, did a lot of searching but could not find an solution.
if you need specific pictures feel free to ask, and i will do my best to make them.

Thanks
Emiel
The Netherlands.

 

[tdonoughue]

Yes, I think some photos of the intake would be helpful. I suspect that you have some cavitation at or before the intake. That would explain why you get good takeoff, but then at speed you are generating air into the intake stream somehow.

But nice job on the rebuild. Looks like a big job.

 

[Scottintexas]

I think I would first try to positively identify what type of pump it is to confirm you have the correct impeller / impeller pitch, while waiting to do that I would also confirm looking around the grate and intake to make sure you don't have any missing sealant to let air in.

 

[Scottintexas]

is this a clean out hatch to remove debris from the impeller ?

 

[tdonoughue]

I believe that is what he calls the 'inspection port'. Which leads to another two thoughts: 1) I would not seal it. You may need to get in there if you suck up a plastic bag or anything like that. 2) A leaking seal here could let in air as well, which would lead to cavitation. However, I suspect this as less of your problem because then I think you would have more cavitation on startup, too.

 

[bronze_10]

Oooooooo this is just the thing that guys here dream about at night.... an unidentified jet with performance issues!

 

[OperationROL]

You have to find out who makes this assembly so you can figure out the impeller specs. I bet the impeller is way out of spec and causing your cavitation. Modifying the wear ring probably helped but not enough to compensate for an out of spec impeller. There are so many people on this site that have determined that visually their impellers are fine and change the wear ring to find little change. I can confidently say that because it happened to me on my previous SX230. I then changed the impellers and all cavitation went away and the performance was back. I would tend to think that if this boat was just used by staff, they were not very particular and probably abused it over time. They probably stopped using it after they damaged the impellers and just left it.

 

[Julian]

Both points above could be the source of your problem.....I'd start with the inspection port...if that isn't sealed it would be the same result as driving a Yamaha with the port removed (which results in you being able to drive at very slow speeds, but when you throttle up it does nothing as it is just sucking air). Since this would be easy to resolve (seal the port somehow-can be a temporary fix), and see if that resolves your issue. If you are confident the port is sealed, then move onto the impeller tolerances.

 

[Julian]

Probaby a Hamilton Jet Model HSRX drive system solely based on this similar size model using that drive....

http://pacificmarine.org/blog/donat...iviera-500-luxury-class-rib-32500-seattle-wa/

 

[Emiel]

WOW Thank you for all the responses,
I Have some pictures off the intake as well of some taken trough the clean out/inspection hatch

Sorry for all the pictures, but that is the most easy way to communicate.

In the last 2 pictures you can see the jet attached to the boat, there is a gap on both sides between the jet and the boat, needs this gap to be covered?
don't worry the wheel isn't touching the grate.
On the 3rd picture you can see the impeller and the begin of the wear ring, does this look okay?
you can also see a little bit of light trough the gap between the wear ring.

Will use silicone to make sure the inspection hatch is airtight,
as for the make of the jet, there are no markings on, the jet was sandblasted and powder-coated, but even after cleaning there was no make or whatsoever to see.
i will search the interwebs for a similar looking jet, especially hamilton,

Thanks
Emiel

 

[Murf'n'surf]

The gap between the impeller blade and housing is definitely causing cavitation and not allowing you to get on plane.

You need to find out what pump you have and make sure it's the proper impeller and not missing a wear ring that would close that gap.

We love pics!

 

[txav8r]

It doesn't take much to disrupt the smooth flow of water from intake to nozzle. A twig, or any foreign object will definitely cause cavitation. Looks like some pretty offensive crud just forward of the intake grate in your pics. That might be a contributor. When you lose the pumps full capacity of water, you introduce air, and lose the hook up of the pump. It will accelerate quick but lack any thrust. Good luck on the repair and getting it running again!

 

[Julian]

It looks to me like there is evidence of a seal between the grate and the hull that you show in the last photos. This could well be a source of air getting pulled in....but hard to visualize where that space leads to and if air could be pulled from the transom forward. Might be worth stuffing something in there temporarily to see if it has a short term result....even if you just put duct tape on it and it lasted 2 minutes.

 

[Scottintexas]

Here is the Ribtec forum site, they might be able to help you better with the type of pump and impeller pitch,
http://www.rib.net/forum/f8/6-5mtr-ribtec-249-yanmar-hamilton-jet-help-please-22835.html

If they don't help I'd try to google the boat model and year to get the pump info, or call a dealer to confirm,

 

[itsdgm]

Just my opinion, but the gaps around the missing ride plate look like a big contributor to the cavitation. Good luck with the repair. Hope it all works out for you.

 

[Emiel]

The gap between the impeller blade and housing is definitely causing cavitation and not allowing you to get on plane.

You need to find out what pump you have and make sure it's the proper impeller and not missing a wear ring that would close that gap.

We love pics!

The space between the wear ring and the impeller is 0.3mm or 0.12inch, is this to much?

Just my opinion, but the gaps around the missing ride plate look like a big contributor to the cavitation. Good luck with the repair. Hope it all works out for you.

Will Make a ride plate, and try again.

It looks to me like there is evidence of a seal between the grate and the hull that you show in the last photos. This could well be a source of air getting pulled in....but hard to visualize where that space leads to and if air could be pulled from the transom forward. Might be worth stuffing something in there temporarily to see if it has a short term result....even if you just put duct tape on it and it lasted 2 minutes.

You mean the front or the sides of the Grate? the front is tight to the hull, but will clean and seal.

Also have a pretty good idea of the make of the Jet-unit, it is possible it is an Eurojet unit,
but all the info i could find is they discontinued to make jets,
and some sites off the bloodhound ssc, and a aftermarket exhaust maker for VAG,
i did send an email to the guy owning rib-shop.com whose name i found on the site mentioned by Scottintexas

Thanks
Emiel

 

[Julian]

I was referring to this image and the gap you see here. I could see this possibly allowing air to be pull from this gap into the intake. And if you look closely at the fiberglass at the front edge, it looks like there was black stuff attached there...perhaps a seal?

 

[Murf'n'surf]

The gap looks far bigger than 3mm in the pictures. 3mm sounds like it would be ok.

Have you looked over the stern while trying to get it up on plane? Maybe it is rising up out of the water too high and since there is no ride plate, it draws air into the intake?

 

[Gym]

I was referring to this image and the gap you see here. I could see this possibly allowing air to be pull from this gap into the intake. And if you look closely at the fiberglass at the front edge, it looks like there was black stuff attached there...perhaps a seal?

@Julian, the only gap I see is between the trailer rollers and the bottom of the boat Is there a gap on the intake I don't see?

 

[Scottintexas]

I think Julian was referring to this area, it looks like there was something attached or stuck to the hull, perhaps a rubber gasket to keep air out, running along the entire mating surface, not just where I marked,