Fiberglass tanks - There was good discussion on SSCA forum:
https://www.ssca.org/forum/viewtopic.php?f=4&t=13824
" selected special vinylester resins that are designed for chemical tanks, and the
interior layer was resin-rich (resin plus cabosil). .... best material for resisting whatever they might decide to add to diesel in the future adoption of additives in diesel, such as in gasoline." (Epoxy does not hold up to these additives)
S.
Steel - under impression
stainless steel does not do well when deprived of oxygen.
Black Iron is fine as long as it is maintained well, i.e,
water kept out, and inspection/clean-out
ports installed, and used. Unfortunately, some boats had the fuel vent on the side of the
hull, which allowed
salt water to siphon, and led to
corrosion. Many are coating the inside of black iron tanks with epoxies or urethane paints. It was recently explained to me by a knowledgeable welder that there is sulfur in diesel, and since tanks are vented there is moisture present (even without a siphoning problem), in combination a dilute sulfuric acid is formed, which degrades the metal over time. Nonetheless, 20 years is decent expected life.
Black iron with
epoxy over the outside worked well for more than 20 years, and would still be viable at 30 if not for the vent issue. (So, with Black Iron, I'd coat inside & outside. A
Trawler skipper in
Santa Cruz is very happy with Master Series Silver
paint as a coating and I'm told by distributor the
fishing boats back east are also using it successfully in this application.)
Aluminum tanks are being used, however they cause pause for some given the corrosive
marine environment.
Some "synthetic" tanks can still have a slight diesel smell penetrate. Moeller has many off-the-shelf shapes, however if they do not have exactly what you need, custom is expensive. Tek-Tanks is a manufacturer in UK, however they are no longer selling into US.
In theory bladders can be fitted, however for large tanks on a
sail boat, there still seems to be unanswered questions, at least in my mind, about how that works out with a large heel undersail. If installing inside an existing metal tank, need to cut out baffles & grind everything smooth. Foam or other strips need to be installed about every 6" inches, and accommodation made for evacuating moisture from the bottom of the tank a bladder is inserted in (like a
bilge pump). Bladder manufacturers usually want you to tell them exactly what to build. Found they were not able to advise a solution based on sketches of an existing tank. Maybe there are manufacturers that are better at that. A newer bladder solution sells the bladder, and
parts, and leaves it to you to install connectors, hoses, etc. Not quite as turnkey as desired in a solution. Only a few years longevity.
May need to think about how a tank change will change weight distribution, and affect overall balance for sailing.
You've probably already found it, but there's a Union 36 and Union Polaris thread in here somewhere talking about tanks.
Please keep us posted as to your findings and determination, as equally interested.
Good Luck.
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