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.