Scarab 195 HO Impulse- Cavitation at WOT

[Brink]

I know there are several threads on this, but they all kind of go in several different directions. My brother and I hit the lake yesterday and the boat started the day fine. While going up one of the rivers since the last huricane, some of the sandbars have moved and we hit some shallow water (low speeds). Shortly after, we noticed at a take off, it would start to cavitate. When backed off of the throttle it will get some bite again, and then I can ease it up to top speed. When loading it on the trailer, I was able to give it throttle, but when time to really push it, the power wasn't there due to cavitation.

Today I went out and removed the pump from the boat, and there is not any severe damage to the impeller. The wear ring does have some light grooves around it, but they don't look very severe.

I bought the boat used with 30hrs on it. This was my second time on the water, and didn't experience anything bad the first time, or even at the beginning on this trip. Only started after getting into that shallow water with sandy bottom.

 

[Brink]

I love the boat though! It will be a lot of fun (I HOPE)!

While the pump is off, should I upgrade to a stainless impeller and wear ring? Hoping the wear ring is the problem, but not sure if that can cause enough water bypass for cavitation.

 

[Rick215HO]

I know there are several threads on this, but they all kind of go in several different directions. My brother and I hit the lake yesterday and the boat started the day fine. While going up one of the rivers since the last huricane, some of the sandbars have moved and we hit some shallow water (low speeds). Shortly after, we noticed at a take off, it would start to cavitate. When backed off of the throttle it will get some bite again, and then I can ease it up to top speed. When loading it on the trailer, I was able to give it throttle, but when time to really push it, the power wasn't there due to cavitation.

Today I went out and removed the pump from the boat, and there is not any severe damage to the impeller. The wear ring does have some light grooves around it, but they don't look very severe.

I bought the boat used with 30hrs on it. This was my second time on the water, and didn't experience anything bad the first time, or even at the beginning on this trip. Only started after getting into that shallow water with sandy bottom.

The wear limit on the impeller/ring is 0.35mm of clearance if you want to check that (new is 0 to 23mm). Use a feeler gauge between the ring and the impeller.
I have had similar issues happen before, usually something stuck on an intake grate, may have come off when you loaded onto trailer.Perhaps others can comment on condition of impeller but does not look too bad to me.

 

[swatski]

I know there are several threads on this, but they all kind of go in several different directions. My brother and I hit the lake yesterday and the boat started the day fine. While going up one of the rivers since the last huricane, some of the sandbars have moved and we hit some shallow water (low speeds). Shortly after, we noticed at a take off, it would start to cavitate. When backed off of the throttle it will get some bite again, and then I can ease it up to top speed. When loading it on the trailer, I was able to give it throttle, but when time to really push it, the power wasn't there due to cavitation.

Today I went out and removed the pump from the boat, and there is not any severe damage to the impeller. The wear ring does have some light grooves around it, but they don't look very severe.

I bought the boat used with 30hrs on it. This was my second time on the water, and didn't experience anything bad the first time, or even at the beginning on this trip. Only started after getting into that shallow water with sandy bottom.

I'm not familiar with BRP pumps and impellers, but that to me looks like classic cavitation/ventilation burns:


I would think that your wear ring and impeller is okay, might be missing sealant or an obstruction, or both, somewhere in the intake tunnel or at the transom plate? Basically - air getting into the tunnel on the intake side. Or the intake is not letting enough water in creating too much negative pressure on that side of the tunnel - and cavitation burns.

--

 

[superboop]

Did you ever fix this issue? I have the exact problem and I would say my impeller is similar condition cavitates at about 6500 and above

 

[tdonoughue]

I didn't have the burns on mine (but @swatski is right--those are classic cavitation burns), but my leading edges looked similar when I pulled my pumps. I just took a file and cleaned them up so they were smooth. Tried to remove material equally so it didn't throw off any balance. Made an unexpectedly huge difference.

I also then went and took some silicone caulk to the intake, where some had fallen out. Another huge difference...

 

[superboop]

Where did you apply the caulk in front of wear ring where the pump meets the fiberglass? What caulk should be used?

 

[tdonoughue]

I used plain (white) silicone caulk. Nothing fancy.

I started outside the intakes. Filled all the areas where bolts were recessed, so the surface was smooth. Then all the seams between the grate and the fiberglass. Then worked my way up to the impellers. Basically, everything that was not smooth, I make smooth with caulk.