Tanks for your ideas

[S/V Alchemy]

In my steel pilothouse cutter refit, I have an unused, approximately 40 U.S. gallon capacity keel tank directly under the engine. Formerly the original holding tank, I had no idea until last week (because access requires that I fly the engine out of the engine bay) if it had been "put away cleanly", only that the people I bought the boat from had a new, HDPE tank next to the head.

I have been considering repurposing this tank as a post-Racor daytank, which would give me a sort of insurance against contamination from bad fuel going into the main tanks, and would extend our motoring range to 140 U.S gallons, or 40% more than now.

Upon finally taking off the inspection plate, I found a few gallons of water...no smell, thank goodness, of either chemicals or of its former usage. I also found significant rust:






I didn't think to throw a magnet down to my wife, who was taking the shots, to determine if the tank was mild or SS. SS would be logical and would match the water tanks I've already pulled out in favour of HDPE water tanks. SS would also (perhaps) suggest that the rust is superficial and could be powerwashed off...not sure if that's the best course.

The other diesel keel tanks forward in the keel are black iron and are full of diesel.

I consider my options as follows:

A) If the tank is indeed SS, I would consider sand blasting the interior and applying a coating (if even needed). To judge by inspection of the lid and the tank top, it is pretty heavy gauge metal.

B) I would consider cutting off the top of the tank, cleaning and coating the interior with something like truck bed liner, and dropping in a HDPE diesel fuel tank with fittings forward (where there is access at the front of the new engine),

C) The same as B), only with a 35-40 gallon fuel bladder. The advantage of this would be the ability to pump out the bladder of fuel and then pull it from under the engine for cleaning or service. It would be secured with bolted-down battens. A clear disadvantage could be the danger from having a working engine directly above this fuel.

Any suggestions, horrible warnings or sage advice would be most welcome.

[GordMay]

Why would you "expect" this tank to be other than mild steel, as are all other tanks aboard?

[hpeer]

Out of curiosity, if it is in the keel, what is around it? Between it and the keel?

Our Brewer has SS water tanks that I removed because I could not keep the compartments sufficiently dry with them in. I now use the keel for dry storage and have a flex vetus water tank.

[Charlie]

I don't have a good idea of what to do with the tank but assuming that you want to have more diesel capacity I would suggest you look at this product. Evapo-Rust Super Safe Rust Remover I have used it and it works great. All you need to do is put immerse the item that you want free of rust and it removes the rust. It used to be sold in powder form to be mixed with water but I don't know if that is still true. The liquid form can be diluted.

[sailvayu]

Steel boat? you sure this is not an integral tank? Just have to ask.

[S/V Alchemy]

Originally Posted by GordMay

Why would you "expect" this tank to be other than mild steel, as are all other tanks aboard?

Because the two 100 gallon water tanks I removed were stainless steel. I still have one unsold. They were great tanks in the wrong place, so I'm going to 4 x 50 gallon HDPEs.

This pictured keel tank was a holding tank originally. Stainless would be a logical choice.

[S/V Alchemy]

Originally Posted by hpeer

Out of curiosity, if it is in the keel, what is around it? Between it and the keel?

Our Brewer has SS water tanks that I removed because I could not keep the compartments sufficiently dry with them in. I now use the keel for dry storage and have a flex vetus water tank.

Honestly, I don't know the answer. The hull itself is mild steel.

I may have to answer that question sooner than later, however.

[S/V Alchemy]

Originally Posted by Charlie

I don't have a good idea of what to do with the tank but assuming that you want to have more diesel capacity I would suggest you look at this product. Evapo-Rust Super Safe Rust Remover I have used it and it works great. All you need to do is put immerse the item that you want free of rust and it removes the rust. It used to be sold in powder form to be mixed with water but I don't know if that is still true. The liquid form can be diluted.

Good advice...thanks for this.

[S/V Alchemy]

Originally Posted by sailvayu

Steel boat? you sure this is not an integral tank? Just have to ask.

Although I have the original drawings commissioned from the designer for the original owner, they do not entirely agree with how the boat is built.

Where the "holding tank" is (and it is plumbed as such) is supposed to be a ton of ballast. It's clearly not there....

[JPA Cate]

Hi, Alchemy,

This may strike you as strange, but I'd lean towards replacing the ballast. I think your boat is likely to sail better with it, it was designed to have it, and maybe you won't need the 40 extra gallons. If you're seeking an emergency "reserve," then a five gallon jerry jug will hold enough to get you into a marina after you've sailed her close to it.

[S/V Alchemy]

Thanks for that thought. It is the path of least resistance, to be sure. I have room to put a more manageable 10 gallon daytank in the engine bay, and that may suffice to have the reserve of "known clean". I could siphon from that to fill jerry jugs as needed.

I even have lead pigs for trim ballast forward. I could put those down the hole and pour cement over them...boom, there it is.