Doug,

I get some corrosion in the bilge where it never gets dry but it looks like mini popcorn stuck to the hull.
Perhaps the black crunchy stuff is over spray from the "pitch" that was sprayed at the factory as a noise/moisture barrier. The engine room most likely is coated with that stuff and then sprayed silver.
Another thing could be that the shower sump has been leaking over the years and Lord knows what has been growing as a result of that nasty water leaking in the bilge.

As for the forward bilge pump running at such a frequency I'd check all through hull fittings like you already did and then inspect the fresh water supply. I'm assuming you have a 41' by your handle. I don't know the routing of pluming on the 41' but I know there is a head and shower up front. Perhaps a fitting is leaking. Do you use the shore water hookup? If so you can turn that off and drain the system and see if the bilge pump still cycles. If your using the water tank you should hear the fresh water pump cycle if there is a leak in the system.

I would have to guess if you had a corrosion problem bad enough to rot through the hull and cause that much water to flow in, you would be seeing sever bubbling/blistering etc all around the boat.

What does your CAPAC meter show??
I'd inspect both ends of shore cord to make sure there is no damage to the plugs and then start inspecting your immediate dock neighbors.
Check for reverse polarity in shore power.
Check for voltage on the earth ground. If there is enough voltage on the earth ground your galvanic isolator will begin to buzz/hum.

I guess ultimately could have the boat pulled and inspect the underside.

-Karl

Couple of thoughts on this.. Some may seem pretty simple and no brainers but here goes.. Check your drain plug in the bow? Maybe it's loose or? The fridge drain line? Maybe it's draining into the bilge or your AC drain line? And just thought of this.. Are there any instances of condensation being an issue, with it being hot out side and our aluminum hulls being cool from the AC? Just crossed my mind.. Has anyone actually ever seen a Marinette where the hull was corroded through? I think it would take a very long time or an enormous blunder for that to happen..
Sean

Again, thanks to everyone for the ideas. This forum is by far the most helpful and responsive of the several that I belong to.

I talked to my storage guy and he said he checks the hull for corrosion every year when he puts it away and has seen none on the outside, so he doesn't think it's corrosion.

I wondered what the bolt I noticed in the bow was all about. I didn't realize there was a drain plug up there. I will give that a closer inspection today. Is there also a drain plug in the rear of the boat?

I store inside unheated, so there may be some damage from freezing. Should I pour a couple of gallons of antifreeze in the bilge when I put it away?

I'm a little concerned about the comment that the front and rear bilges are separate. I have two bilge pumps in the rear and only one up front. I was taking some comfort in the knowledge that if things went bad, I had 3 bilge pumps on board. It appears, in case of the worst, I am depending on that one 23 yr old pump up front, is that right?

I believe the front and rear bilge were designed to be separate, but one never knows. If you store inside why should there be a water issue? I'd replace ANY bilge pump that old!

Does your shower sump pump work properly? If not, alkaline water from the shower will gather in the bilge, corroding it from the inside. I know of at least one Marinette that was badly damaged in this fashion.

Jeff

Norm
One thing it is not, is my holding tank. Courtesy of a bunch of good guidance from the forum last fall, I replaced my old one with a new plastic one that is working great.

Jeff
We never use the on-board showers, so that shouldn't be a problem, but I am going to go out and buy a new bilge pump. I'll save the old one, which is working perfectly, for a back up.

I talked to John Althouse today, and he, too, thinks it's something other than through hull corrosion. He was very helpful and I appreciated him returning my call so promptly. It might be interesting to take a road trip to the UP sometime to see the plant. Has anyone ever been there?

Doug

Sure glad U got that $$hitty job outta the way. That’s one U can scratch off the list of possibilities. Don’t use the shower Huuummm

Norm,

Big s Live On

Check out the "General Category" and go back 10 or 11 pages to Oct 21 of last fall and look for the posting called "Leak in Holding Tank". There are 35 posts there that I exchanged with various folks who helped me through the process of replacing my holding tank.

I had to remove some of my floor boards in order to get to the holding tanks because they have to be slid a few inches in order to get the tank out. I had to remove my hot water heater and a strut in the floor in the cellar space. I was able to slip my new tank in through the cellar door.

I ordered the hold tank from Plastic-Mart.
http://plastic-mart.com/...lipWsnqMCFRMeDQodGxeykQ
I used a 52 gallon tank model number 48W. It was a bit bigger than my old one. Even though it worked for me, I would recommend you measure your openings to be certain it works for your boat. It just barely slipped in through my cellar door with some twisting and turning. The tank was around $300 but there were some extra costs for the threaded holes.

I did it alone. The toughest part to do alone was removing the old tank as it was much heavier than the new plastic one. There were some posters who did not recommend plastic, the best part of plastic from my perspective is that I can now open the cellar door, shine a flashlight on the top of the tank and I know exactly how much room is left in my tank before I need a pump out.

Good luck
Doug

Not a minor difference there!

Jeff