Underpowered Islandia....again...

[steenbeen]

A couple of years ago I sucked up some rocks that did a lot of damage to my impeller and wear ring. I replaced both of them and it seemed cured, after I adjusted my trim plate down with about an inch of threads showing. There was (what I thought) minor damage to some stator vanes but I did not replace that.

99% of the time, it is only my wife, me, and our 2 children, so power is never really a problem. Last weekend, we took it out with 4 total adults and 3 little kids (less than 4). It took forever to get on plane and sounded like it was cavitating. Now, I'm thinking that the damage to the stator vanes is causing this, but wanted to pass it by y'all before I send it in to impros (and am out a boat for 3 weeks).

I have the original "weed-free" grate that I need to use around here because of all the curly leaf pond weed. I can hear/feel when it gets clogged and when the weeds get sucked through, so I know that it's not weed buildup. I tried the "rock" grate a while ago, but it clogged too easy and I kept having to go for a dip, so I put the original back on.

Here are some pictures of the stator, impeller, and wear ring. Could this stator vane damage cause a pretty significant lack of power?

 

[Coastiejoe]

Looks to me that the gap is substantial. Can you measure it with a feeler gauge? Basically, if it is thicker than a dime the wear ring and or impeller if it is worn or has been filed needs replaced.

 

[Sportster-2001-951C-Stock]

Yes, the obvious is true. You now are operating with a narrower margin for operator error thus as a result, you have to be more conscious of overspeeding the engine and applying throttle in a manner that avoids cavitation during acceleration. I'm convinced you must be less aggressive during acceleration until the issues are resolved.

I would also reconfirm the impeller is properly matched to the hull and powertrain, there are several impellers available for the sportjet b/c they were installed with various engine and hull combinations. One size never fits all when it comes to marine propulsion, mismatches are a common and expensive mistake.

 

[Dr Honda]

It's hard to tell from the pics.

The wear ring looks nice... but the gap between it and the impeller seems a little large.

The stator veins in the sportjet don't seem to cause a huge issue when they are warn... but they can contribute to loss of acceleration.


With that said... and owning an Islandia... were all the adults trying to sit in the back? (under the Bimini top, out of the sun) If that was the case... then you were just grossly out of balance, and it's hard to get enough thrust to push the nose back down without a trim nozzle.

I throw my boat around like a monster JetSki... and when I have a bunch of people on-board... I just move some to the forward seats, and the boat drives great. If we are all in the back... you have to roll into the throttle to keep the "Traction" going, and eventually the nose drops, and we get up on plane.

 

[steenbeen]

The wear ring and impeller are both pretty much new, with maybe 20 hours on them. The impeller is a solas from impros.

How much play is the impeller shaft supposed to have? After I pulled the stator, the shaft has quite a bit of play, so the picture was showing the top gap when the shaft was at its lowest point, actually touching the bottom. Of course, after the stator is back in, the gap is even all around.

As for weight distribution, it was pretty even with 2 adults & 1 kid up front and 2 adults (including me) and 2 kids in the the back.

The impros guy (David I think) seems to think the stator damage is sufficient enough to cause significant acceleration loss.

 

[Coastiejoe]

I would still measure the gap. New does not mean there is no issue. If the impeller was made 5-thousands of an inch off, that is half the issue... If you can move it to touch one side, then the gap should not exceed 20-thousands. Or, use two 10-thousands gauges and put them on opposite side of the impeller.

 

[Dr Honda]

Run time on the impeller is kind of irrelevant. I've seen pumps with hundreds of hours on them, that look new... and some with a few hours... that got dragged though a gravel field... and are totally beat. BUT... you pump and impeller look great !! Just try to center it, and measure the gap. The tighter the better.


As far as the play in the shaft... it will move a lot on the sport jet. Your stator assembly is the rear bearing that supports the shaft. SO... DO NOT push the pump shaft around too hard. You could damage the seal on the gearbox.


Finally... don't take the opinion of IMPROS as the gospel. Over the years, I've seen WAY too many times where they sold the wrong crap, and then wouldn't take care of the customer. I'm not saying they are a bad shop... but they are in business to make money... and the people here do it for free.

With that said... I'm not saying that the warn stator won't cause SOME issues... but it's not the source of massive cavitation. Cavitation comes from air entering the pump. That air can be a leak around the housing... sucking air around the hull (it can happen with a heavy boat) or you are physically boiling that water via low pressure on the back side of the impeller. (Once again, easy to do with a heavy boat) So... next time you have it out... try pushing it to half throttle... let it build a little speed... and then roll the power on.

I guess I should ask... was it sitting nose high when the cavitation was bad... or relatively flat, and just wasn't going?? (you may want to put your trim tab down some.

One thing to keep in mind... the Mercury SportJet isn't a creation of SeaDoo. It's an engine and drive that anyone could buy. So... if you hit sites like "Scream and fly", "Boats.net", "Seadoo sport boats" or "iBoats"... you will see a lot of threads with info on these drives. And generally... we have found that fixing bad spots in the stator doesn't change the output that much. But... it's aluminum, so it can be welded up, and filed clean.

 

[Sportster-2001-951C-Stock]

Cavitation occurs when the water moving through the pump actually boils, due to pressure differential around the edges of the impeller. Too much space between wear ring and impeller can aggravate cavitation as well as stator damage.

Ventilation is air being sucked into an impeller from outside. This can happen if there are air leaks or the boat is incapable of fast acceleration due to being too heavy. A heavily loaded boat will take more time to accelerate thus it's much easier to ventilate AND/OR cavitate the impeller. Too much throttle too quickly can cause either of these two, condition of the pump also plays a big part.

When propping that powerhead in outboard form, we consult the manufacturers recommended WOT RPM at speed to determine if the prop is a good fit and adjust this variable until the engine is operating within the range.

That's the right way to judge if the pump/prop/impeller are reasonably matched to engine power b/c it compensates for the hull and weight of the boat.

So if your pump is a little hurt, WOT RPM may be out of engine operating range and top speed will not be where it should. Put enough weight in the boat and apply too much power too quickly, it will take longer to reach plane than if you ease into the throttle due to speed helps load the pump intake with water and keep intake pressure up to avoid cavitating (boiling of water due to high pressure differential) and ventilation (sucking air from around hull). A pump in excellent condition will not cavitate as easily as one that's not in top shape.

 

[steenbeen]

I'll measure the gap tomorrow. 2 years ago, right after I replaced the wear ring and impeller, I accidentally flattened out the trim plate (prompting my first emergency "HELP ME" post to this site, as I was on vacation 5 hours away from home at the time. Adjusting it down so about an inch of threads showing between the housing and nut helped tremendously.

I may try Aquaman's extended trim plate as well...

 

[steenbeen]

I just measured the gap on either side of the impeller. I measured on the very rear of the blades by setting 1 feeler gauge under (so it was resting on it) and measured the opposite blade. I could fit the 0.018" gauge on both sides at the same time, but not the 0.019". This size of feeler gauge is rigid enough that I cannot accurately measure anywhere but the very rear.

The book I have says that the out of spec number is 0.100", which is huge. It says that the clearance between the impeller and wear ring should be between 0.038" - 0.058". So according to that, I am much tighter than the book specs...

 

[Dr Honda]

Yep... the spec on the Merc engine is bigger than the Rotax boats. Under 20 thou, is good.

If you get the extended ride plate... let us know how it runs on the islandia.

 

[steenbeen]

I attempted to sell my boat and when it went to the local mechanic, it was discovered that the boat is taking on water. I have not talked to the technician that found it, but it is apparently pouring in between the hull and exhaust on the port side. They drained about 30 gallons out of the bilge when they took it out after 15 minutes on the water. The technician thinks that the extra weight in the bilge, along with the damaged stator vanes are causing the power loss and long time to plane. I don't watch the bilge pump outlet, so I don't know if the bilge pump is constantly running or not...

The dealer thinks the engine needs to be removed to repair this leak and estimates between $2,000 and $4,000 to do the work. Has anyone seen this before and knows of a fix that does not involve removing the engine?

 

[Dr Honda]

Selling the boat?

Yep... expensive, but that's what a dealer charges. But then again... I don't listen to mechanics. A lot of them are on the shady side. (That's why I do my own work)

 

[Sportster-2001-951C-Stock]

Sounds like it might need a replacement gasket on the powerhead mounting flange.

 

[Tomfrmnh]

30 gallons in 15 minutes is a lot of water. Pulling the engine isn't as bad as it seems. I just did this on my Challenger to replace the gasket between the engine and drive housing. It was leaking but not at 30 gallons in 15 minute rate. You may have a damaged housing or bad seal between housing and the hull. Back the boat in the water on the trailer and try and get video of where the water is coming in. If it's coming in at that rate it should be pretty evident. If it is the gasket between the engine and housing the gasket is $26. Buy yourself an engine hoist on Craigslist. It shouldn't take you too long. If the housing is damaged or the leak is between the hull and the housing the repair may be a little more complicated. But you need to find out where the water is coming in.

 

[steenbeen]

Well,

I finally got the boat back in the water today, albeit still hooked to the trailer but floating.

There is indeed water coming into the bilge. I couldn't get a video since it was quite dark and I didn't want to clog up the ramp. It is coming in fairly fast directly underneath the expansion chamber while the engine was not running. The battery died on me, so I couldn't start it to see if it got worse while it was running.

From the manual that I've been looking at, there are 2 different bolted connections below the expansion chamber, both presumably with a gasket. Is this where you are talking about Tom?

 

[Tomfrmnh]

Yes. However, there are actually three places it could be coming from. The expansion chamber itself is bolted to the motor flange (engine adapter) which is bolted to the pump housing. Mine was leaking right where the motor flange is mounted to the pump housing (right under the expansion chamber). I would try it again with just the fresh water flush hooked up. Again try and get a video if you can. I will pm you my video so you can see.

 

[Dr Honda]

If the engine wasn't running... I'd have a hard time thinking is was actually coming from the expansion chamber. But as you said... there's a couple "Layers" there.

Unfortunately... since the engine wasn't running... I would be pointing at the hull seal, or even a small crack in the hull where the engine/drive mounts.

Just an FYI... on my personal boat... I had a leak around the exhaust, hull fittings, and I original thought it was engine issue. (it was hard to see) Then, I finally got a nice sunny day, and spent some time looking. At that point... I found it was an easy fix. (but a shop won't do that)

 

[Tomfrmnh]

Here is a link to the video I took in the bilge. What you are looking at is the starboard, aft side of the engine. The boat was on the trailer with the fresh water flush hooked up. This was very helpful to me as I was able to study it by slowing and replaying several times in the comfort of the couch and not curled up in impossible positions in the bilge. You can see at about the 2 sec mark at the bottom left of the screen and again at the 9 sec point exactly where it was leaking. This was the gasket between the engine adaptor and the pump housing (engine adapter needed some JB Weld to fix a gouge right where it was leaking) It was a $25 part and the o-rings were another $5. I bought a used engine hoist on CL for $125 and needed the lifting eye for $35. So for under $200 and about 5 hours of labor I was fixed.

http://youtu.be/epwCeUpQRDY

 

[steenbeen]

I think I found the problem with the water ingress into the bilge. It appears that the jet drive cover is cracked on the very aft section, just below the expansion chamber. I will have a video soon to show you what I think I found.


https://www.youtube.com/watch?v=vK6_2lGvCKI

 

[Dr Honda]

Yep... I agree. That's very strange. I don't think I've ever seen a mount crack like that.

I would yank the engine, and get a better look. If that is the problem... it can be welded.

 

[steenbeen]

I'm going to be pulling the engine this weekend. Anyone have any pointers on pulling the engine?

 

[Dr Honda]

Nothing in particular. It's really an easy engine to get out. I pulled my engine faster than I can get a little Rotax out of a ski.

One thing that comes to mind..... If you are using an engine hoist, you need about 6" more length than the standard puller has. SO... you will need to extend the boom. But be careful with that. If you go more than needed... you will also need to extend the legs so it doesn't fall over forward.

Also... the deck lid doesn't have to be removed. Just pop the gas struts, and it will go vertical.

 

[steenbeen]

Well, I finally got around to pulling the engine and removed the jet pump cover.

Here are a couple photos of the crack that goes around the entire aft portion of the jet pump cover, directly below the expansion tank. Hopefully I can find someone that can weld this thin aluminum. I'm not really sure what could have caused this other than sucking up some rocks a couple of years ago. The crack appears to be at a weak casting point maybe, but not too sure...

 

[steenbeen]

Well, I finally got around to pulling the engine and removed the jet pump cover.

Here are a couple photos of the crack that goes around the entire aft portion of the jet pump cover, directly below the expansion tank. Hopefully I can find someone that can weld this thin aluminum. I'm not really sure what could have caused this other than sucking up some rocks a couple of years ago. The crack appears to be at a weak casting point maybe, but not too sure...

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