[CaptainForce]

I replaced my two 55 gal steel tanks with aluminum tanks about 14 years ago. I agree with the comments about not painting and not installing the anti-siphon loop. I would add that it's a good practice to secure the tank with good ventilation outside and beneath the tanks. My tanks are sitting on starboard runners that are fastened with screw heads well reccessed and not other metals fixed to the tanks; however, there are tabs welded to the tanks that are then securely fastened.

 

[CaptainForce]

I did say, "loop". I think I just type this by rote after "anti-siphon"; however, what you present in the photo is the same item that was formerly within my diesel pick up lines from my tank. I drilled out the balls inside these one-way valves. For the first year after the install of my new tanks I was able to run well on one tank, but the other would often cause my engine to stall after about twenty minutes of running at 2500rpm. I've heard of others having problems with these valves sticking and I did not want the insecurity of having my fuel supply blocked at some innappropriate time,- like breaking an inlet at the rocky jetties!

I should add that the one tank pick-up never stuck and many may never experience a problem. I guess there may be different qualities of the production of these valves.

 

[CaptainForce]

On the subject if fuel tanks, we just discovered our catalina 309 (2008 year) tank is corroided on the bottom. We are shocked that a six year old well kept boat would have this problem and we are baffled how moisture may have gotten into the space.

Please clarify for us if this was an aluminum tank and the nature of the bottom surface. Was it flush with wood, fiberglass, on runners or otherwise ventilated.

 

[CaptainForce]

I understnd the risk of the corrosion of aluminum tanks next to a hull that gathers moisture from condensation or at wet bottom surfaces without good ventilation. I would be concerned about corrosion from the bottom inside the tank and wonder about the cause; however, I'm not sure how one determines that the corrosion originates from inside the tank. I'd like to hear the method that would be used to determine wether the corrosion begins on the inside or outside and also, what thoughts knowledgeble people might have about additives in diesel fuel that might corrode aluminum.

 

[CaptainForce]

............. The inside of the tank where the leak was looked like a termite/acid ate away an area approximately 3/8" in diameter from the inside. The outside of the tank looked like a tiny crack. The exterior surface was flush. It was pretty obvious even if my description isn't clear.

No, this is clear and well said. I think the thought that the inside of the tank having a larger surface area of corrosion than the outside would be compelling evidence.