fuel tank and coffin question

[Ebwalk]

I just purchased a 1989 Mako 231. After a big rain, the space in the fuel tank inspection cover aft of the seats was full of water. Maybe I overreacted, but I propped up the console and pulled the cover (deck) off of the tank exposing the top of the tank. It's gross and clearly been wet a long time. Does it matter that the foam on the sides had been wet? How can I tell if the tank is in good shape? I now understand there is a drain for the top of the tank (guess my was clogged), but that still means the foam would get wet. that seems like a bad design. I don't want to put it all together again just to have the tank fail next season!

Thanks for your comments.

[wolfie]

I agree, it's a bad design. Unless the coffin cover is perfectly sealed (almost impossible) water gets in and can't get out. Any space not filled with foam holds water against the foam, which eventually absorbs some amount. The wet foam then accelerates corrosion of the tank.

I don't know if you could pressure test the tank in place, would be a careful operation for sure. As far as I know that's the only way to tell if you have any holes now. (Other than smell test for gas) Doesn't tell you how much life might be left though.

If you're planning on keeping the boat for long, I'd say replace it. Especially if you've already got access to the tank. Just doing a tank on this model should be pretty easy, plenty of similar threads here. The problem is once you start digging in there is always more to do...

[gmcauliffe]

If your tank is not leaking into the bilge, then a pressure test is not going to tell you much more.

Meanwhile, a 30 year old tank is nearing borrowed time, and could still be one corrosion pinprick away from failure, and no test would tell you that.

So if you've already got it open, put any test money towards just replacing the tank. And absolutely replace the fill and vent lines at the same time because those also have known corrosion and failure issues.

A note on the design--these coffins vented top and bottom, so at least the only water remaining is what's next to or in the foam. Sure you could /try/ and completely seal the coffin, but that never works perfectly, and then the water can't get out. IMHO, better to have a top air vent inspection hole, a bottom drain, a good coating of coal tar epoxy, and denser closed-cell foam to block it in.

You'll sleep easier this way, rather than trying to delay the inevitable.

[gmcauliffe]

If your tank is not leaking into the bilge, then a pressure test is not going to tell you much more.

Meanwhile, a 30 year old tank is nearing borrowed time, and could still be one corrosion pinprick away from failure, and no test would tell you that.

So if you've already got it open, put any test money towards just replacing the tank. And absolutely replace the fill and vent lines at the same time because those also have known corrosion and failure issues.

A note on the design--these coffins vented top and bottom, so at least the only water remaining is what's next to or in the foam. Sure you could /try/ and completely seal the coffin, but that never works perfectly, and then the water can't get out. IMHO, better to have a top air vent inspection hole, a bottom drain, a good coating of coal tar epoxy, and denser closed-cell foam to block it in.

You'll sleep easier this way, rather than trying to delay the inevitable.

[Triplecrownnc]

Agree its time to replace the tank, its past its usable life. Most people do not routinly inspect the tank or the sealant around the tank lid, that sealing will leak over time and will allow water on the tank. Remember a bottom drain in the coffin to let water out is also a way for water to get in from the bilge.

[Triplecrownnc]

Agree its time to replace the tank, its past its usable life. Most people do not routinly inspect the tank or the sealant around the tank lid, that sealing will leak over time and will allow water on the tank. Remember a bottom drain in the coffin to let water out is also a way for water to get in from the bilge.

[Ebwalk]

thanks for the replies! I found a tank manufacturer speedytanks.com

who gave me a great idea to cut the foam out: pressure washer!

And here's a good article on aluminum tank corrosion:

http://marinesurvey.com/yacht/fueltank.htm