Rusted fuel tanks

I had been hoping the fuel tanks were still serviceable, I knew the tops were badly rusted but not no holes appeared when I scraped the loose rust off.

There was a lot of rust on top of the tanks I spent about an hour scraping with a very large crow bar and vacuuming the loose rust.

However when I removed the partition surrounding the starboard tank I found it was leaking at the bottom.Notice the stained black area, it has been leaking for some time. I actually got lucky here, when I started to cut the tank the hole opened up much bigger.
So it was time to cut the tank out. I tried all the various cutting tools, 3" and 4" grinder with carbide cutting wheels, jig saw with metal cutting blade, but the fastest turned out to be the acetylene cutting torch....

I did cut the first section off the front of the tank with the grinders, so I could clean the last of the diesel out.
The white you see in this picture is paper towels buried in the much that was in the tank. Doesn't look like the tank was EVER cleaned. Which is a real shame the sides and most of the bottom of the tank were just fine. It was just in a few spots in the bottom 1/3rd of the bottom panel that had rusted.

I don't know of any way to reliably repair those spots. There was a layer of rust in the muck. The real shame is that there was a drain plug at the lowest corner of the tank. All this could have been prevented by just draining  the water out every 6 months or so.

So we decided that while we had the boat all torn apart we should go ahead and replace the tanks.

I started with the metal cutting angle grinder disks. It was very slow frustrating work, the 3" cut much slower but the disk lasted much longer than the 4" disk. After cutting 1/3rd of the front side off I cleaned that section out and went to it with the torch. Only had to put a few fires out during the process. The worst was when I cut the baffle to the next section out. I tried unsuccessfully to wash the dirt out with the spray nozzle on the hose, but there was still gunk left that caught fire. But the hose was handy and successful at putting the fires out.

It took about  2 days to cut the whole thing up. First the front then the sides and baffles. Then I could bend the top down enough to cut it into section. That left the bottom and back side(up against the hull). I ended up putting pieces of steel I had cut out under the bottom to protect the hull while I cut the bottom up. I had the garden hose right at hand the whole time. I also made sure to keep the areas of the hull near the work wet. It all worked out, no burns to the fiberglass.

Tank removed, pressure washed and ready to start building the new tank. We have decided to put 4 tanks in, 2 to each side. Yes it will cost a little more and be less convenient when filling, but I like splitting the tanks up so each does not carry so much fuel. I estimate that the old tanks held around 400 gallons  each. I am planning to carry about 600 gallons in 4 tanks. That will give me more room for other equipment. At 4 miles per gallon that is a cruising range of 2400 miles. We are not planning on crossing the pacific!!