Thanks for the picture. I do not want that to start happening anytime soon!

Is there a speed that this becomes more prevalent or can it happen anytime?

What grit sandpaper did you use?

Does blueprinting the lower get rid of the potential of cavitation burn?

Thank you for the help!

That pic is what usually happens when you run positive trim with an Imco shorty. I've looked at a lot of them and most had the burn there to some degree. Wilson says that they can get you 2-3 mph with their blueprinting. I tried to copy their work but it is not truly blueprinted so speed gain was minimal. I was more out to fix the cav burn issue so I had the burn welded up and the rear of the water inlet welded up. I streamlined the angle of the bullet quite a bit too. The scotchbrite pads will clean up the entire surface pretty nicely. I followed up with 320 grit wet sandpaper. IDK what is going on with yours but it doesn't look like cav burn to me and your drive doesn't look too low to me. A close up high resolution pic of your problem spot might tell more.

As far as the speed, IDK. I do know that the damage in my picture happens when I trim up to get maximum speed which on my boat is 83-85 mph.

I wonder if you are trimmed in such a way, at a certain speed (not necessarily top speed) that water is hitting the top of the lower and running over it... that would cause the low pressure area.

Is there anything in the way to cause a strange water disturbance going to the drive? water pickup, tranducer, etc.

Thanks for the additional information. I will try to get a high res close up and post it.

In the meantime I will look into the Wilson blue printing, maybe this will be a good, do I dare say, winter project.



I was told to install a flush drain plug in the box. The person who suggested this is on a race team. I wonder if that is causing a slight disturbance? Other than that there is nothing else down there.

I talked to a guy at Wilson and they are the real deal. They are set up to give a quick turnaround and won't take your drive unless they are ready to do the work immediately. A single is $2,000 I believe. I wanted to do it but with business down this summer I decided to give mine a go myself. http://www.wilsoncustommarine.com/Page_2_6OGO.html

Thanks for the link.

Update....

I unplugged the Mercathode and it stopped. The boat hasn't been in the water for more than 3 days straight for a long weekend. Still kind of confused but at least I isolated the cause for now.

Interesting, mine looks the same, as I've stated no extension box and don't have to run excessive trim, I might try unplugging mine as well

Good to hear! Have you any ideas on how to squeeze a few more MPH out of it?

Short of putting a Whipple on her, no. :angry-smiley-038::lolhit: