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Re: [PSUBS-MAILIST] Coating for ballast tanks



Fiberglass tanks do away with the corrosion problem and were used for years by Hyco. Aquarius and Curasub are both equipped with them (and all the Pisces boats). There is just no telling how many dives the little A-boat has done over the decades, and it's still diving with the original three mains. That said, it is a structural issue that I know very little about.

Perry, on the other hand, used 316L for MBTs and painted them on the outside only. Internally, they never showed the first vestige of rust. Those babies were heavy, though, like Frank's. You have to budget for them, weight wise.

The Nektons use(d) mild steel tanks with some overlap against the hull, and I'm paying the freight for that with repairs.

If you are, in fact, figuring on mild steel, or a combination of SS welded to the pressure hull, then take a lot of time to work it out so the acute corners are minimized. Make your access ports large enough to get in there with strong light to look for pinholes and paint blowout over the welds. And do a thorough inspection and repair every year!!!!! More often if needed. Honestly, I wouldn't do it that way in the first place. Welding a back sheet on and bolting the tanks to the pressure hull isn't much more weight and allows both for easy removal and protection of the hull itself.

As a for-instance example, my K-350 had pits half the depth of its hull material thickness! Not good. I did a thorough mapping of the hull and sonic thickness testing to verify. It wasn't pretty. Including the bilge repairs, we burned 50# of 7018 doing overlays on all that. And then had to grind more than half of it off to get back down to an approximation of the original shell thicknesses. I wouldn't wish that job on ANYBODY.

Vance



-----Original Message-----
From: ShellyDalg@aol.com
To: personal_submersibles@psubs.org
Sent: Wed, Aug 25, 2010 11:13 am
Subject: Re: [PSUBS-MAILIST] Coating for ballast tanks

An interesting idea was offered some time back on using "Rhino Coat" like is used for pickup truck beds.
The company has several products available for different applications. One of their products is specifically designed for boat hulls. There was information on their site about this coating being used on salmon trawlers and other large commercial fishing boats with good success.
As I recall, the life expectancy was over ten years with proper maintenance and doing minor repairs to the coating was straightforward if the instructions were followed.
 Now, a boat hull is a lot easier to access than a closed ballast tank and Vance's suggestion for making access hatches large enough to get tools and materials inside the tank is a good one. I have often thought about putting a "window" of 1 inch thick plexi on each of my ballast tanks for inspection.
As you know, my ballast tanks are 12 gage 304 stainless but rust is still a problem. It just takes longer.
The tanks and mounting system are configured for easy removal. It takes about an hour or less to remove a ballast tank or re-mount it on the sub. Still, it would be handy to have an inspection window so watching for early signs of corrosion, checking for mussels, or maybe a little kelp gets sucked in there.
The cost of stainless sheet versus the work involved in repairing/replacing a corroded tank is something that needs to be addressed at the "design stage" of a sub project.
Anyway, the Rhino stuff sounded interesting to me.
Frank D.