Question on broken cavitation plate on 4.3 Mercruiser Stern

[dburne]

Hey gang,

I have a question regarding the cavitation plate, or anti cavitation plate - not sure what it is called, on my Mercruiser 4.3 MPI Stern Drive.

Ok so as you know from my other thread, last Saturday was a wild day for us with the motor ending up not starting at the end of day and stereo not working. Got that all squared away at the Dealer this week, snafu on my part hooking up batteries wrong.

Well one more thing happened. We had a lot of rain the week before, and the lake was up like 5 ft. When we put in and started cruising up the lake, I apparently hit a submerged log of sort. Now after heard and felt a large thump, I stopped the boat and checked it out. The prop was ok, everything appeared ok. When we got to the other end of the lake where we anchor in our favorite cove, while I was swimming I checked the boat out as good as I could , everything appeared ok. When the boat was running, it ran great.

So yesterday, after picking it up at the dealer , I noticed the plate on the left side of the stern had a large chunk out of it, kind of a half moon shape. Below is a pic of it. Now, keep in mind also I tried starting the boat in the driveway earlier this week with the muffs on, never noticed this. But after getting it from the dealer, now I see a large chunk missing out of it. I am sure though, it had to be because of whatever I hit, maybe I just did not notice it prior as I was so pre-occupied on the motor not starting..

Anyway I asked the dealer about this, he said they know a welder that can get a piece welded back in there and smoothed out, and will never even notice it. He said would be best to get that done when I bring it in to get it winterized in the off season.

Below is a pic of the issue - should I be overly concerned about this?

Thanks for any suggestions,

 

[bbwhitejr]

I know it can be welded and the repair will look good. However, I would certainly think you would have noticed that hooking up the muffs and after all of the looking over it you did. I have no doubt that I would have noticed it!!!!!!!!!! I would bet it got bumped at your dealer....

Someone else will chime in as to whether you are OK to operate it like it is for a while.

Bennett

 

[dburne]

Yeah I keep scratching my head over that one, I mean I went over that stern really good while it was in the water ( was swimming with life jacket), I know I ran my hand all over both sides of that stern, and I certainly did not notice it with the muffs on when I tried to get it started afterwards in the driveway...

My wife is saying the same thing, she says no way would I not have noticed that...

But, the fact is I did hit a submerged piece of wood , and can see where it struck the front of the stern - there was some wood in the speedo hole. So I guess it is possible it did this, though how I did not notice it is beyond me.

We will be heading back out to the lake early in the am, will be interesting to see how it handles.
Not even a scratch on the prop. Weird.

 

[thegotoguyr]

I do not believe you would have hooked up muffs and not noticed that. Maybe it got cracked in your encounter and rattled off on its way to the dealer? I'm pretty sure it will affect the handling in some way, or at least fuel consumption, that's a pretty big chunk missing. My omc had a piece missing smaller than that and I couldn't tell any issues when running. I fixed it anyway. I would expect a pull on the steering wheel but I think you could still run it.

 

[DiSH]

Hard to believe that hitting something in the water while underway would cause damage in that area that would be significant enough to break it off. Think about the angle of impact as you move forward in the water. Also, I think you would have noticed it while checking. Anyway, no I don't think it will cause any major issues, but yes I would get it fixed.

 

[dburne]

Well we have been out on lake about an hour. I ran it pretty hard for
about half an hour. Seems to run and handle fine.
When I picked boat up at dealer the tech noticed wood in the speedo hole in
the stern. He took a drill to it to clean it out just before I left.
Now the speedo does not work. It is stuck on 20 mph.

Lol I can't win. But it is running good!

 

[blaster]

I busted the anti ventilation plate on my old sting ray. I had similar damage but the prop was also trashed. In my case it couldn't be welded and the housing for the lower unit was replaced. You must have hit it just right to do that, sorry about the bad luck. If the boat runs normal and doesn't blow out in a turn then fix it later, just in case you hit something again.

The speedo pitot probably has debris still in it. Use a drill bit just slightly smaller than the hole and try to clean out the gunk by hand. If its on the drill you may damage it if your not very careful.

 

[dburne]

I will give that a try thanks. The tech used a drill on it.

 

[BillK2632]

Yes use a drill bit or piece of wire to clear the speedo hole - never use a drill, tech should know better. The drive should be useable with the broken cavitation plate. It can be fixed and you will never know it was broken. Cast aluminum is brittle and will usually break before it bends. I know you hate this, I would, but try not to worry, go boating and fix it when you have time. I feel pretty certain this was due to the log strike and didn't happen at the dealer.

 

[dburne]

Thanks for the advice guys. Yes she is running great so I am not going to
worry with it for now. I will get it repaired in the off season.
I will see what I can do with speedo before next outing.

Having great day! Hi is going to be 98 and mostly sunny. My wife is a sun bunny so
she is loving it!

 

[sibnai1]

glad to hear that you are back on the water, I'd say the CP was probably cracked (hair line fracture) by the strike and was on there and finally broke off on your commute to the dealer, I'd also get it repaired, I'm thinking you have a SS prop maybe that is why the prop did not get damaged from the strike??? and you probably have a splinter of wood in the speedo pitot and that is why the gauge reads 20 mph and does not change. As others have said clear out with a small pick tool or drill bit and wet dry vac