Outboard paint damaged from running bilge pump?

All,
I was caught out in a thunderstorm over the weekend. I ended up having to run my bilge pump for probably 20-30 minutes because of the heavy rain. When I got my boat back and was washing it, I noticed that some of the paint seems destroyed (looks like water spots that are eaten down to the metal). I am very sure the paint is actually gone. The paint was in very good shape before and I have had the boat out numerous times before without this happening (but not running the bilge pump for an extended period).

The motor is a 2005 mercury 50HP. The self-sacrificing anodes (under the bracket and trim tab) are in good shape.

Is there any way that stray currents from the bilge pump motor could have caused this? If so, how can I prevent it in the future?

Thanks in advance for any help!

Joseph

Re: Outboard paint damaged from running bilge pump?

I can't see a cause and effect. Exactly what paint was damaged?

Re: Outboard paint damaged from running bilge pump?

Thanks for the reply. It is actually the paint on the metal drive shaft housing right above where the lower unit bolts up to it.

I am sort of having trouble seeing a cause and effect as well. I am not sure whether the bilge pump is grounded to the boat or has a dedicated ground back to the fuse block.

I was just thinking that maybe some return current ended up going through my motor to the lake water instead of back to the battery. I am sort of stumped on this one as well.

Re: Outboard paint damaged from running bilge pump?

The pump should be grounded at the battery.
It should have not caused corrosion in that short of time anyway..I have never heard of that problem myself...

Re: Outboard paint damaged from running bilge pump?

Pictures might help.

Re: Outboard paint damaged from running bilge pump?

Thanks. I will take some pictures tonight and post them. Good suggestion.

Re: Outboard paint damaged from running bilge pump?

just a wild guess... but any chance you forgot a strap/tie down/bungee cord or something like that hanging off one of the eyelets on the transom? Maybe something was hanging off there and banging away at the motor while underway. Or the last time you trailered. (?) Or maybe a transducer broke loose? My dad once caused damage to his brand new truck by having a loose end of rope (which had a metal ring cinched onto it) banging away in the wind. It looked like a bunch of stone chips.

something banging the motor seems much more likely to me than electrolysis of some sort.