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I replaced the aluminum fuel tank in my 1973 Outrage a couple of years ago. At that time, I added a small , 1", hole for access of a small pump and for inspection. Most of the times I checked there was a small amount of water in the bottom of the cavity. Assuming I had a leak in the deck, I pressure tested the cavity, no leaks. Well this summer I left the boat covered, still water in the cavity, more than ever. Too make a long story short, the water comes from condensation. Every tank in a sealed cavity is getting wet from this source, not leaks. The solution is to leave the covers off of the deck to let air circulate, this helps greatly, but what a pain. The temperature difference between the inside of the cavity and the exterior air going across the deck can be huge. So for me, the mystery is solved.

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Actually, most fail from the inside out, usually from water/ethanol sitting in the bottom of the tank. I've seen 2 pristine-looking tanks now with tiny pinholes at the lowest point in the bottom rear of the tank. The only evidence of a hole was a wet area on the outside of the epoxy or whatever coating was on the tank.

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I've only seen a few tanks myself, not counting those posted here, and all have failed from the outside, none, from the inside.

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I am curious how you seal the tank cavity? I don't see how that is possible unless your caulk around the fuel lines. Does anyone do that?

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Is climate a factor in tank failure. For example, is a tank far less prone to failure installed in a boat in New Mexico where the relative humidity is far less than in Florida? Or is the day/night temperature delta a more significant factor.

Is venting a fuel tank cavity a more effective preventive measure than draining a cavity? Many outdoor stored boats are covered for the off season. When I stored my boats with covers I provided plenty of ventilation to avoid condensation under the cover. My goal was to prevent mold forming on the boat and it was effective. Would that also help prevent fuel tank failure?

Walter has an interesting perspective and he is an experienced owner. I would like to hear other opinions on the subject.

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The tank setup on the early boats is such that the two points where the fuel fill and delivery pipes enter and exit are sealed tight with caulking, making the tank cavity waterproof, as long as the the tank access cover and the tank cover are sealed properly.

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I'm not sure how the routing is under your console on the Outrage but by design any water that runs behind the fuel/vent hose cover on the port side is directed under the deck. The tank is foamed in so the water is supposed to run across the tank and supposed to exit through a hole in the tank cavity into the Starboard side rigging tunnel. Water on the deck that runs behind the Starboard side cover also drains into the same rigging tunnel. The design was to have the tank cavity drain into the rigging tunnel, then drain out the starboard side sump while underway if the plug in the drain sump is removed. This also works backwards flooding the tank cavity if you have the drain sump plug removed and the boat is not on plane.

This all sounds good if you believe the foam in the tank area does not absorb water...But we all know now that is fantasy the designers led us to believe.

It is very important to remember when the the drain sump has water, the rigging tunnel has water which will run backwards into the tank cavity.

I was successful in sealing my tank area on my 1980 22 foot Revenge. I did this by running all of my control cables and wiring along the gunnels instead of the Starboard side rigging tunnel and sealed the floor under the helm console.

To change and seal the Gas fill/vent hose design, I made a manifold out of aluminum tubes shaped in elbows. Both the fill and vent tubes are welded through 1/4" aluminum plate for the base which is shaped to fill the gap of the floor where the original fuel/vent tubes passed through the floor. This plate made it easy to seal and impossible for water to pass through and get under the floor.

This way, I could stop both the fill and vent hoses above the floor attached to the top of the manifold, and under the floor run the fill/vent hoses from the tank to the underside of my manifold....Works perfect, the tank fills/vents as normal.

But, you also have to block off the other side behind the starboard side cover as well. I made another manifold for that side, but that side doesn't need the strength so used two pieces of 1/4" ply and fiberglass/epoxy for the base instead of aluminum. I then ran/sealed a 1" aluminum tube through that base as well. Through that tube I ran the tank sending unit wires and grounding wire up through that manifold and through a bilge hose on top of the deck/manifold. I then looped the bilge tubing with the wires inside up to gunnel height so water cannot get down in the tank area but the tank area will still vent. This will all fit behind the starboard side cover.

I actually brought an additional tube up through that Starboard side manifold (so there was two tubes) for my raw water wash down supply input but that is a different subject.....

To prevent rigging tunnel water to work backwards I sealed the hole where the tank was originally designed to drain into the rigging tunnel.
I then went one step further and made a wall in the tunnel under the deck (with a plug for inspection) blocking off the rigging tunnel from the starboard drain sump. It is/was no longer needed..... No water can now get to the rigging tunnel and the drain sump can work as designed to drain the deck.

To inspect the tank cavity for any leaking I installed a 1/" drain tube between the tank cavity and the stern fish box.

I replaced the fuel tank without foam and increased the strapping system to hold the tank in place using 1X2" aluminum square tubing along with 1/4 aluminum angle to make it impossible to move. To test it this summer and make it available for inspection without sealing the floor down, I used duct tape to seal the decks and fished it throughout this summer....Kind of a mickey mouse way to seal/test it but everything worked as designed. This next spring I will pull the decks, do a final cleaning, and seal them down.

If you pull the deck to replace the tank on the older single deck Revenge models....I highly recommend that you cut the deck just behind the console's so you do not have to pull the consoles to access the tank in the future.

This system worked great for a Revenge, but I don't know where the rigging on the Outrages runs under the deck. I would assume there is a hole in the floor directly into the rigging tunnel from the console. If this is true, you could use a similar design as mine, seal the floor around the tank cavity and fill the drain hole between the tank and the rigging tunnel. In that situation, and if you use an in tank fuel gauge, it would be way more simple. You would only have to make the manifold for the fill vent hoses and Seal the floor around the tank cavity.

I believe the manifold cost me roughly $150.00 to have made. You will have to add a small vent tube to the manifold though; so pressure in the tank cavity can expand/contract/breathe....As I said above, mine breathes on the starboard side.

With the Revenge, I had the option and went the route I did sealing the rigging tunnel off because I didn't want to seal the floor around the tank cavity. That seal will be a major pain to break loose the next time you need to remove the deck.

Vance