How to replace fuel tank?

[massnspace]

Hello

I am considering making an offer on a sailboat that has a large aluminum diesel tank fitted under the settee. The make is not relevant to my question.

Here is the situation. The boat is 40 years old, and the tank does NOT leak. But. I have owned 2 other sailboats with aluminum tanks that either leaked when purchased or developed a leak. On those boats the tank was very easy to pull out and repair/replace.

But the boat in question has EXTENSIVE, high-end woodwork everywhere. As a professional woodworker I can see this.

In order to remove the tank, one would have to:

-remove massive amounts of custom woodwork all around the settee and built in cabinetry above the tank. There are hundreds of carefully bunged screws that would all have to be drilled out.

-remove the teak and holly sole (it is solid teak and holly, not plywood with a teak veneer).

-remove the 3/4”plywood subfloor.

-cut out several large stringers that are glassed onto the hull sides and run on top of the tank.

-reverse these steps after fixing/replacing the tank.

I am not even sure it would be possible to remove all the woodwork without damaging a lot of it. So buying more wood and trying to machine it and color match it to the existing wood might be necessary. I think this project would take months and be very very expensive, if it could even be done.

There is no other area of the boat that could easily accept a new tank. At least without, again, major reconstructive surgery.

So. Any ideas?

As crazy as this sounds, I was thinking of the following….cut the entire bottom of the hull out directly under the tank. Lower the hull piece and tank out. Replace tank. Raise and carefully align the cut out hull piece back into place, taper edges, epoxy/glass in and fair. On the inside of the boat, there is access enough to get some tabbing in here and there, but NOT possible to add glass tape around the entire perimeter of the seam. So of course it would be weaker than original structure.

Again. The woodwork in this boat is absolutely amazing. It’s one of the reasons I am considering buying it. I would not want to have to destroy it for the sake of the one tank.

Ideas?

David
Seattle

[deblen]

You can cut aluminum with woodworking power tools easily-eg: jigsaw,skilsaw,etc.
Can you cut a big enough alum. tank "panel" out to allow installing a "bladder fuel tank" inside the old alum. one?

[SV Confianza]

We will have the same problem on our boat if our tank goes. It’s behind a custom made closet and various glasses in parts all around.

I have read articles of people cutting the top of the tank, removing the baffles and de-burring, then putting in a bladder type file tank. I’m not sure that will even be possible on ours, but that was my only lead.

[mvweebles]

Originally Posted by massnspace

...... As crazy as this sounds, I was thinking of the following….cut the entire bottom of the hull out directly under the tank. Lower the hull piece and tank out. Replace tank. Raise and carefully align the cut out hull piece back into place, taper edges, epoxy/glass in and fair. On the inside of the boat, there is access enough to get some tabbing in here and there, but NOT possible to add glass tape around the entire perimeter of the seam. So of course it would be weaker than original structure.

Unless the boat is metal, that's a really, really bad idea. If it's metal, it's only a bad idea. There is simply no way to get the hull adequately reinforced.

Common way is to cut out old tank as previous poster said. Replace with multiple smaller tanks and/or live with reduced tankage.

A well installed and maintained tank will not leak for a very long time. Typical death is from deck leaks, either teak decks or from around fill neck. If neither of those are present, you may be okay.

[massnspace]

I thought about a bladder, but I don’t think I can even get into the top of it. Also, if the tank has baffles, the bladder won’t go in….

[massnspace]

Originally Posted by mvweebles

Unless the boat is metal, that's a really, really bad idea. If it's metal, it's only a bad idea. There is simply no way to get the hull adequately reinforced.

Common way is to cut out old tank as previous poster said. Replace with multiple smaller tanks and/or live with reduced tankage.

A well installed and maintained tank will not leak for a very long time. Typical death is from deck leaks, either teak decks or from around fill neck. If neither of those are present, you may be okay.

Why such a bad idea?

If the new glass is scarfed in properly with a 12:1 feather (or more), and epoxy is used, I am thinking it will be very strong. Especially if one could also add some heavy biaxial tabbing (as much as possible) to the inside. And of course add thickened epoxy to fill the gap between the cut core when rebuilding….

Of course it would be weaker, but that area of the hull is not subject to high loads. Of course a whale of something could directly hit it, but the chance of that is so minimal….and if that happened I would argue a normal hull would break anyway….

[massnspace]

Originally Posted by SV Confianza

We will have the same problem on our boat if our tank goes. It’s behind a custom made closet and various glasses in parts all around.

I have read articles of people cutting the top of the tank, removing the baffles and de-burring, then putting in a bladder type file tank. I’m not sure that will even be possible on ours, but that was my only lead.

If one has to cut off the top of the tank, then that means one would have to remove everything to get access….and at that point why not just replace the whole tank?

Again. I don’t think it would be possible to easily remove enough cabinetry to even add a bladder.

[Bowdrie]

There are multiple thousands of older boats with remarkably high-quality woodwork in them.
Can't save them all, find one that won't drive you to ruin.
Designers who fit tanks such as you've described need to be beaten with a rubber hose.

[massnspace]

Originally Posted by Bowdrie

There are multiple thousands of older boats with remarkably high-quality woodwork in them.
Can't save them all, find one that won't drive you to ruin.
Designers who fit tanks such as you've described need to be beaten with a rubber hose.

Not correct.

Many boats have plasticy or plywoody interiors. It is the rare one that has properly built, high end joinery that looks great after 40 years.

[boatpoker]

If ... IF ! ... an aluminum tank is properly installed, there is no reason for it to suffer from very much corrosion damage at all. I've surveyed lots of boats with 40 year old aluminum fuel tanks in excellent condition. I've also seen under 10yr old aluminum tanks corroded right through due to poor design and/or installation.

[massnspace]

Originally Posted by boatpoker

If ... IF ! ... an aluminum tank is properly installed, there is no reason for it to suffer from very much corrosion damage at all. I've surveyed lots of boats with 40 year old aluminum fuel tanks in excellent condition. I've also seen under 10yr old aluminum tanks corroded right through due to poor design and/or installation.

Since 2 of my previous boats had leaking tanks I assumed that it was somewhat of a common problem.

Does the moist environment of the bilge affect them? (Most boats have some water in the bilge and most tanks are mounted low down.) I have also heard that any water particles in the diesel would attack the aluminum…..?

Is there any way, apart from a visual inspection, to check if a tank is good or not?

By the way, both of my failed tanks failed at the corner welds….

[Jammer]

The usual solution is to cut the tank apart in place and remove it in pieces, and then replace it with multiple, smaller tanks. You don't necessarily have to get at it from the top, maybe the sides or the ends. There may still have to be some removal of cabinetry. Sometimes it makes more sense to cut access holes where they are needed and then patch them (elegantly), rather than disassembling everything.

[boatpoker]

Originally Posted by massnspace

Since 2 of my previous boats had leaking tanks I assumed that it was somewhat of a common problem. Does the moist environment of the bilge affect them? (Most boats have some water in the bilge and most tanks are mounted low down.)

Is there any way, apart from a visual inspection, to check if a tank is good or not?

If the aluminum is in contact with salt water that becomes stagnant, it will corrode.

If the fuel pick up is not very close to the bottom and water sits in the bottom of the tank, the tank will corrode.

If the tank is in contact with wood, it will corrode.

If any tank fittings are of a different metal, it will corrode.

If dirt and dust sitting on top of the tank gets wet and is left to sit, the tank will corrode.

Hopefully the tank has inspection ports where you can see the lowest point of the interior where corrosion is most likely. If not buy a decent borescope/endoscope ($40 - $60) that you can insert it into the tank and can also reach it all around.

You are looking for white aluminum oxide like this ....

[SV Confianza]

Originally Posted by massnspace

If one has to cut off the top of the tank, then that means one would have to remove everything to get access….and at that point why not just replace the whole tank?

Again. I don’t think it would be possible to easily remove enough cabinetry to even add a bladder.

Ah yes, we are a bit different. I *might* have access to cut the top off. There's some room over part of the tank that's accessible behind an inner door inside the closet.

[gonesail]

i have turned down boats because of embedded and inaccessible fuel tanks. and water tanks. it's not if they fail .. it's when.