new diesel fuel tank

[Dave9111]

If a steel tank like that only has rust in the bottom seam, the logical thing to do is cut out the seam and weld another piece across the bottom.

Steel is really easy to weld. Aluminum a little more difficult.
Replacing a tank is not always the right solution. That would be at least $750 for that tank in the US in Aluminum.

I wouldn't try and make that tank out of fiberglass. Too time consuming.

Welded polyethylene is also an option.

I know it turned out to be an inlet leak. But since you have it out, clean it up and put on some good paint!

Dave

[Rotten Ricky]

Hi Bjor,

There seems to be a blind spot in the boating industry with vessel manufacturers even today installing unsuitable aluminum and steel tanks. Crazy! A quick search will show that I have written on this subjects many times in favour of replacing tanks with fibre-glass versions. Patching tanks made of a flawed material is not a smart idea.

In summary:
- non-rusting or other deterioration
- non-sweating which reduces chance of growth in diesel
- non-conductive for spark ignition (with gasoline fumes)
- readily-made and repaired by commercial business or yourself.
- last almost forever. Underground gas/petrol station tanks have a 50 year warranty! It is used for acids and many other nasty industrial purposes.
- cost far less than aluminum - my commercially made gas tank cost only 60% of aluminum version, with far greater tankage for the space.
- easy to make yourself with very little guidance for probably 10-20% of the cost of aluminum. Use polyester resin for diesel, vinylester/epoxy for gasoline/petrol. It is not rocket science - just common sense and care. Same for holding or water tanks.

Good cluck and cheers,
RR.

[CarinaPDX]

@Rotten Ricky: Since fiberglass with polyester resin is somewhat porous what would you use to seal the inside of it? (I once saw an old ChrisCraft hot-vac'ed for blisters, and it drew diesel through the hull from the integral diesel tanks - obviously not well sealed.)

I have been fussing over a new day tank. The space is similar to the OP's so pre-fab tanks are out. In the U.S. custom plastic tanks are out as they don't meet vapor permeability standards (production roto-molded tanks have a sealing layer on the inside). My space is more curved then the OP's, so any welded aluminum or SS tank will either lose a lot of potential capacity or be a complicated curved or piecewise linear design. Any tank will have to fit through an opening that is smaller than the space so will limit the size.

I have an integral tank in the keel beneath the engine, made of bulkheads and top glassed into the hull, and apparently lined with gelcoat. It has never been a problem so perhaps creating a fiberglass tank in place would be the best solution. It would be very difficult to work there though. Any thoughts?

Greg

[greensail]

We had a 40 year old Hallberg Rassy 42 with 2 diesel tanks. The main tank is GRP and is integral with the hull being basically the after part of the bilge with a bulkhead and lid glassed over it.

It was built pre epoxy days with polyester resin and gelcoat and has never been an issue. An advantage is there are no gaps between the tank and hull so the tank is substantially larger.

Also, having a deep narrow bottom, any sludge or water accumulates in a small area and is easy to pump out with a permanently fitted hand pump.

The water tank is built the same way, forward of the bilge well.

Our new boat has a leaky mild steel tank and I am planning to build a new tank in fibreglass in the same way, as an integral part of the hull. It also saves having to remove removing a whole lot of furniture to get a tank in.

[Rotten Ricky]

Originally Posted by CarinaPDX

@Rotten Ricky: Since fiberglass with polyester resin is somewhat porous what would you use to seal the inside of it?

I have been fussing over a new day tank. The space is similar to the OP's so pre-fab tanks are out. In the U.S. custom plastic tanks are out as they don't meet vapor permeability standards (production roto-molded tanks have a sealing layer on the inside). My space is more curved then the OP's, so any welded aluminum or SS tank will either lose a lot of potential capacity or be a complicated curved or piecewise linear design. Any tank will have to fit through an opening that is smaller than the space so will limit the size.

I have an integral tank in the keel beneath the engine, made of bulkheads and top glassed into the hull, and apparently lined with gelcoat. It has never been a problem so perhaps creating a fiberglass tank in place would be the best solution. It would be very difficult to work there though. Any thoughts?

Greg

Hi Greg,


Most hand-laid-up polyester and glass is non-porous IF WELL-SATURATED and using multiple layers of cloth/light roving. I think most issues with porosity are from poor workmanship and the use of chopper-guns in mass production - yielding too much resin and too little glass - hence the woes of blisters etc in hulls. You probably know that gelcoat is porous, having millions of little interconnected bubbles in it.

If you want to be further assured, use vinylester resin (being a blend of polyester and epoxy) or just epoxy resin, or give your polyester tanks a later coat of epoxy inside - pour in a half litre/pint and rotate it until you are sure of good coverage.

Just so everyone knows, diesel will not affect polyester but gasoline/petrol will attack it, allowing tiny glass particles to be freed into the fluid, so it is essential that the inside layer of resin is vinylester or else it is epoxy-coated later. The difference in cost of resin might come into play of you were mass-producing tanks, but for a one-off, really there is not much difference in the overall cost of the job so just go with vinylester or epoxy. Then you will know your tank will handle anything.

My tank was for gasoline and it never showed any deterioration in about 20 years before I sold the boat - or the 12 since that time. I know the present owner.

In water tanks, food grade epoxy is available - leaving no smell or taste.

I would recommend that you make a self-contained tank that does not use the hull etc and is therefore not affected by the hull requirements or movement under way or damage. If a built-in tank springs a leak you might have serious problems. A separate tank unit can be removed, repaired or replaced on a workshop bench - not in the awkward or inaccessible bottom of a hull. And there is the issue of repairing with new resin that is trying to adhere to glass that was covered with by fuel.

For my tank, I spread waxed paper against the compound curve of the hull and then laid up some glass cloth using epoxy resin - as polyester will attack and wrinkle the paper etc. Then I built the rest of a dummy tank pattern that maximized the tankage for the area. This also proved that the resulting tank would actually fit (!!!) and the manufacturer made a tank from that pattern. Perfect fit.

If you have an awkward spot, maybe consider two smaller tanks to maximize the space available and connect with hoses between them. This has the advantage of being easier to handle and maybe easier to make and install. Also you will be able to isolate one in an emergency (depending on your connections and valves) and also you may not need to install baffles to stop fuel sloshing around inside a larger tank. However you need to put some serious thought into the surprising amount of room needed for connections, valves etc.

Sorry but I know nothing about govt regulations in the US, but I do know that my insurance co. is fully aware of glass tanks because they are less-hazardous than steel or aluminum, and if they approve them, then I imagine that they are in compliance with any regulations in Canada.

Lotsa fun on boats!

Cheers, RR.

[CarinaPDX]

@Rotten Ricky: Thanks for the input. I was talking to a boatwright friend last night about doing this in epoxy and glass. He could do one in place but it would be thousands of dollars, because of the labor as much as anything. It would be a better result, with higher capacity and a long life, but I'm not sure it is worth that much. An aluminum tank would likely be less than a thousand. So I will be thinking a bit more about it.

Greg

[Rotten Ricky]

Originally Posted by CarinaPDX

@Rotten Ricky: Thanks for the input. I was talking to a boatwright friend last night about doing this in epoxy and glass. He could do one in place but it would be thousands of dollars, because of the labor as much as anything. It would be a better result, with higher capacity and a long life, but I'm not sure it is worth that much. An aluminum tank would likely be less than a thousand. So I will be thinking a bit more about it.

Greg

You are the one to make the best decision, based on a multitude of factors of which I am not familiar. Whatever you do, try to anticipate and have a procedure for any unintended problems. Inexpensive extra valves etc can pay off in an emergency. These things WILL happen.

I wish I was near you and I we could make your tank for $100, as most of this is common sense, familiarity and a bit of confidence. But I keep forgetting that I have a lot of experience in glass, and I forget the cost of labour, as these small projects are all fun for me. I am building a similar thing for a boat neighbour right now - for a the cost of resin and glass and couple of beers. Incidentally, the 6 cu. ft holding tank I built for my boat will be installed shortly. You can be sure that with the nuclear-like potency of the intended contents, it is VERY robustly built!!!
Cheers and stay safe, R.

[Bill Seal]

I was thinking about replacing my leaking fuel tank with a f/g or plastic one, but my wife mentioned that since the tank sits right beside the engine, it wouldn't be too smart to use a flammable material for the replacement.
I'm going with aluminum.

[sanibel sailor]

Looking at the pics, I would have that bottom corner whacked off and a new plate welded over it. No significant volume loss and the corroded part will remain problematic.
I replaced the 35 gallon steel tank in my Bristol 35.5 about 8-10 years ago. There had been a deck leak at some point. It had rusted on the top surface and allowed water in, but didn't leak diesel out. The new tank is aluminum and sits high and dry above the prop shaft.
As a benchmark, the guy said aluminum tanks were about $8 per gallon at the time.

I took the old tank to show him as well as detailed scale drawing. They still made it upside down on the first try.

[Rotten Ricky]

Greg,

If you go with aluminum, as you know, the biggest problem is corrosion from inside from water accumulation - as happened with my previous tank. The welds are often particularly vulnerable due to the change in metallic composition caused by the welding process. I suggest that the tank be welded so that the top panel is left to last. This will enable you or the welder to scuff up the inside surface and apply one of the protective sealants on the market that others have suggested, especially on the lower part of the tank. I would also try to apply it on the outside to help prevent corrosion from locations where the tank is supported, or possible immersion. Try to keep air circulation around all outside surfaces. You might get small extra tabs or layers of aluminum welded on wherever the tanks will touch anything else. Minimal cost for maximum benefit.

This is a time to think long term, especially as you can use it as a selling feature when the time comes. We know that anyone with this kind of fore-sight will likely treat the rest of the boat in the same meticulous and trustworthy manner, encouraging the sale. The small cost of the treatment will pay off handsomely through trust. Document it with pics.

Cheers, RR.

[sanibel sailor]

Welders that I know would be reluctant to weld on a tank that has had a surface treatment due to possible fumes, weld contamination, etc.

[Rotten Ricky]

Originally Posted by sanibel sailor

Welders that I know would be reluctant to weld on a tank that has had a surface treatment due to possible fumes, weld contamination, etc.

Good point, though I was not actually suggesting welding the applied area in the lower portion of the tank - where most corrosion takes place - and I would protect that scuffed and cleaned area while the top was being welded on. One could even fill it with clean water while welding the top panel was taking place.

The other idea is to scuff and clean and protect the lower area, pre-cut an access hole in the top panel - which should be there anyway for future inspection and maintenance and inspection - and only then pour in and apply the protective sealant. The perimeter of the hole should have at least a double-thickness for fasteners to get a grip.

The same principals apply to repairing a steel or aluminum tank when the bottom is cut off for re-welding. Always prepare the surfaces while you have good access, not after contamination from use and when access is difficult.

That is why built-in tanks that use the hull etc as members of the tank can be such a problem.

After 40 years of sailing and repairing boats, for every job one needs to think three steps ahead for future ease of use and repair. It pays off big time, including positive impressions for a future resale. All of us want a boat that has the indications of being thoughtfully well-cared for - often at a very small extra cost - and we will pay higher prices for that comfort!

Cheers, RR.

[BlueH2Obound]

Originally Posted by Bill Seal

I was thinking about replacing my leaking fuel tank with a f/g or plastic one, but my wife mentioned that since the tank sits right beside the engine, it wouldn't be too smart to use a flammable material for the replacement.
I'm going with aluminum.

The material in a cured fiberglass tank may be COMBUSTIBLE, but is not FLAMMABLE. Big difference.

Also, just curious, isn't you HULL f/g? You know, the hull 6" from the bottom of the engine?

[Bill Seal]

My thought was more like a blown out exhaust elbow melting a hole in a polyethylene tank and catching the spraying liquid fuel on fire. The tank on our boat is BESIDE the engine, not below it.

[Bill Seal]

This thread seems to have gotten becalmed in the Horse Latitudes, but I'll give it another try: The tank I'm having made will be about 20w x 15 long x 20 high. Most aluminum tanks appear to be 0.080" material, does this seem to be too thin, and would 0.125 be recommended?, or am I being OCD.