Should I plug this limber hole?

[v8George]

I know everyone's first response is "hell no" but hear me out. I have 2001 Monterey 262 Cruiser that had a corroded aluminum fuel tank. A few things contributed to it. The prior owner never used the main switched bilge because it stopped working and relied on the backup bilge. This allowed water to routinely get higher in the bilge than it should, letting water enter the tank coffin. The limber hole in the tank coffin was set higher than the bottom of the enclosure so once water got it, it never got out.
Once water was around the fuel tank, it corroded and the aluminum oxide formed powder which mixed with water and became paste. This paste clogged the limber hold and the tank sat in this nasty stew, corroding it badly.
I was getting a fuel smell so I stuck my finger in the limber hold and a flood of nastiness came out.So, I removed the cabin floor and firewall panels and pulled the tank.
Thank God I did as the tank was just about to let go, I actually poked my finger through it.
This is what the tank looked like.

This mess is what the coffin looked like.

I vacuumed it and you can see the high water line and also see how the limber hole is mounted high.

I scrubbed it out with bleach and water and noticed it wasn't draining even with the boat tilted up.

 

[v8George]

I also noticed the gelcoat and glass was in bad shape around the hole so I ground it out, lowered it, and reglassed everything.

This is where I am now with new glass bedded in, new bilge paint.

The drain is only about 2" above the bilge so it appears that the design exposes the tank to seawater all the time.
Here is my question:

Do I even need this drain if the coffin never sees water? My other thought was a removable plug.
I just don't want to do this again in a few years.

 

[Woodonglass]

I'd prolly enlarge it so it would extend to the two lower channels on either side of where it is now to ensure proper drainage and seal it up well with epoxy and bilgecoat. I'd also highly recommend coating the NEW tank with a product like POR-15 to ensure it never corrodes again.

 

[gm280]

Okay, I know there will be a lot of back and forth comments on this one. I can see both issues myself. On one side I can see a totally sealed tank area to keep water, especially salt water, out and protect the tank. On the other side, is there really a true way to seal such an area completely so if any salt water did penetrate the area it would drain? I don't know which way I would go. If there are any holes in the tank cavity to allow fuel to go in and out and of course wires for the sending unit, I can easily see how water could get in there as well. Because it is not sealed in those areas. And even one time of salt water intrusion will spell the same issues quickly as well... I'm sure others with better knowledge will chime in with their ideas and suggestions. But the ultimate choice is still yours! JMHO!

 

[v8George]

I have actually put myself to sleep several nights reading up on painting versus non-painting. The new tank is in primer. I considered drilling another set of holes where the slots are, but I already ground out and reglassed a slope into the edge, hard to see in the photo. Once the tank is in, there is a small access panel that has an opening for the filler and vent, that is the only way water can get in if the lower hole was blocked. I am almost considering installing a plug in the limber hole but that would require constant monitoring so I don't end up with the same issue of trapped water.

This is the old tank with the access panel removed. There is a wooden panel that has a large notch cut out to clear the filler and vent, that is the only way water could get in. The hatch you are looking through has a perimeter drain and the canvas is always up so it shouldn't see heavy weather.

 

[kcassells]

I would build a subfloor on the bottom even if it meant reducing the size of the new tank. And use that area below the subfloor as a channel for water to escape and not have any business touching the gas tank. I might be wrong but I believe it is code not to have any outlet in coffin {mechanical perhaps} to give fuel a chance to leak into other compartments..A Boom.

 

[v8George]

The new tank is identical to the old one with the exception of being .125 instead of .090 thick. I can't get much higher, it hits the decking. I could possibly double up on the plastic strips.

 

[kcassells]

Oh well.... Water is water. Maybe cut a pc of 3/4" pvc, perforate it and cut in 1/2 and use that as a directional to the bilge with the dbl strips. You need to move the water off and away from the tank. Doesn't matter much what you protect it with IMHO. Use a mechanical plug and let it bleed out daily so you can determine that no fuel is getting into the other compartments.

 

[kcassells]

On another note, completely seal the tank from deck so ther is no intrusions and close the plug. Alot of tanks are done that way. No need for all the related apparatus you mentioned to be there anyway. Just a thought.

 

[bigdirty]

My $.02 is to always have drainage. Its a boat, and water can and WILL find its way in just about anywhere, given the right circumstances. Best to have a way for it to leave.. I also like to have or make easy access to as many areas of the lower hull/keel as possible, just to keep an eye on things ya know?

 

[kcassells]

My $.02 is to always have drainage. Its a boat, and water can and WILL find its way in just about anywhere, given the right circumstances. Best to have a way for it to leave.. I also like to have or make easy access to as many areas of the lower hull/keel as possible, just to keep an eye on things ya know?

I agree with BD...in all areas except a gas tank. Thats why they call it the coffin. But the way the original tank set up is/was...justs sits in water alldatime even with the limber hole. So thats whats the issue. How to move the water so the tank isn't sitting in it again and corroding. Technically the tank should be contained in case of a leak so nothing gets into other compartments and a possible boom. Any advice would be appreciated. Getting old.

 

[bigdirty]

....sitting in it again and corroding. Technically the tank should be contained in case of a leak so nothing gets into other compartments and a possible boom...

So as I see it, the only way that tank would develop a leak is due to corrosion.. which would be caused be water sitting in there, as it did.. so this can just go around and around...and the factory obviously built it like it is/was... To move any water that might get in there, you have to have a drain (the hole) or possibly a bilge pump.. but hey, then IF the tank were to leak, you would be pumping fuel overboard, which would be quite bad as well.. :lol:


I guess its the same sort of issue, that I disagree with, that caused my boat to rot out; No drainage from front/cabin to rear bilge.. also another 'technicality' and supposed code for boat building.. And my current boat had the same issue developing as the fuel tank was sitting in water that could not escape. I have now raised it slightly (from the total rebuild of stringers and bulkheads), and created drainage below it, from the cabin right through. If there is some room to do so, I'd defiantly raise the tank up as much as possible on rubber or plastic supports in this case, and just keep an eye on it from here on out..

 

[v8George]

Oh well.... Water is water. Maybe cut a pc of 3/4" pvc, perforate it and cut in 1/2 and use that as a directional to the bilge with the dbl strips. You need to move the water off and away from the tank. Doesn't matter much what you protect it with IMHO. Use a mechanical plug and let it bleed out daily so you can determine that no fuel is getting into the other compartments.

That gave me a sort of crazy idea. What if I got some 6" PVC, cut it in half and molded it to the contour of the floor and glassed it in place with a drain plug on the aft side? That would protect the tank but still give me an easy visual inspection and a means to drain it if water did get in.

 

[zool]

Mine was built with a removable plug on the cabin wall bulkhead, forward of the coffin, but an open hole aft, to the engine bilge....water never got into the under cabin area, bit engine bilge water would drift forward, under the tank, I had some corrosion to deal with.

I see no problem with a removable plug aft also, you can just pull it at the end of each season. or incase of a catastrophic situation. I do have pumps forward and aft of the coffin box though.

That gravity drain design you have looks reasonable.

 

[gm280]

The real problem I see is everybody wants a fix and forget proposition and that is really hard when you are talking abut a fuel tank and salt water. Unless you have either a plastic fuel tank or one made out of stainless steel, you will have to be constantly keeping a good watch on your tank forever. There is no fix and forget with such a situation. For every option you can think up, there are ways to compromise it too easily. So make whatever you choose to where you can open it up and see what is going on throughout the year... JMHO!

 

[v8George]

I am leaning towards re-purposing the old fuel tank by cutting out a section and using a V-shaped piece to dam off the limber hole with a drain plug on the bottom instead of a half pipe.
I would paint the bilge side with bilge paint and leave the inside aluminum.
This would keep bilge water out, let me monitor any water in the coffin, provide a drain, and give me an idea of the overall health of the tank since its the same material exposed to a similar amount of water.

 

[Mikeopsycho]

I'm with Zool, removable plug gets my vote.

 

[Woodonglass]

HMMM, how are you going to "Re-Purpose" that old corroded fuel tank? Don't you think it's beyond repair???

 

[v8George]

HMMM, how are you going to "Re-Purpose" that old corroded fuel tank? Don't you think it's beyond repair???

I am going to cut a V-shaped piece out and make a dam similar to the drawing above. The bottom material is horribly corroded but the top 85% of the tank is in excellent condition.

 

[Woodonglass]

Well, good luck. Repairs on fuel tanks here on the forum, have not had good results in the past. I hope yours do. If this is the only area of the tank that has corrosion issues then it may be well worth the attempt. I truly do, wish you well:rockon: