mild steel diesel tanks.

I had to replace the tank on my 20 year old boat this autumn as there was a persistent drip. When I removed the tank I found that the base had become porous in one area.Now replaced with a plastic tank.
 
I replaced mine when I bought the boat, it was 23 years old but had obviously been leaking for a long time before as evidenced when it was cut up for removal - there was a layer of epoxy? In the base. I replaced with a plastic Vetus tank.
 
Too many variables, thickness of steel, quality of welds, enclosed invisible areas. My tank, 5mm steel, 1976, has been a mass of rust since I bought the boat in 1992. One maybe helpful 'fact': 10mm of rust destroys 1mm of steel, but it's the pitting that gets you.
 
How long is a piece of string question. As others have already said it is usually localised pitting that causes problems, often from water creating damp patches in inaccessible places such as bearers that tanks sit on as well as from condensation internally. So not uncommon to go in less than 20 years, nor to last more than 40. Best to replace with plastic in most cases when the old one rots.
 
I have the same problem. I think it's a case of reassuring yourself really.

My boat was in very regular use until I bought it which (hopefully!) means there was very little water in the bottom. But I really need to replace it next Winter. The thought of being at sea with a bilge full of diesel is not appealing.

It's bound to be expensive as it is it will need the yard to lift it. Has anyone costed a mild steel replacement? How does it compare to plastic?
 
Ruffles said:
I have the same problem. I think it's a case of reassuring yourself really.

My boat was in very regular use until I bought it which (hopefully!) means there was very little water in the bottom. But I really need to replace it next Winter. The thought of being at sea with a bilge full of diesel is not appealing.

It's bound to be expensive as it is it will need the yard to lift it. Has anyone costed a mild steel replacement? How does it compare to plastic?
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The mild steel replacement for my Moody 31 - a "like for like" drop-in replacement with all pipe fittings, dip tubes etc. - cost something like £400 (it was 2 years ago, and I don't have the invoice to hand). Perhaps a less complex shape would have been cheaper, but would have meant a lot more fiddle trying to fit it! It was also done as a rush job, so I probably paid a premium for that.
 
laffinskip said:
Are stainless steel much more expensive?.
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Most of the cost will be labour so the additional cost of the material may not be great. However there is no need to have a metal tank as a custom made plastic tank will be a similar price to stainless and if you can fit it a standard size tank much cheaper. Superior to metal in most applications.
 
Tranona said:
Most of the cost will be labour so the additional cost of the material may not be great. However there is no need to have a metal tank as a custom made plastic tank will be a similar price to stainless and if you can fit it a standard size tank much cheaper. Superior to metal in most applications.
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All true, but isn't welding stainless a more skilled operation than welding mild steel? Any engineering shop can do a workmanlike job in mild steel, but a shop that can work in stainless may be harder to find and therefore more expensive.
 
laffinskip said:
Are stainless steel much more expensive?.
Click to expand...

Cannot comment on price of a stainless steel tank as my Westerly had one already fitted by the original owner.
He had no end of trouble with the factory fitted mild steel one, so had the stainless made so it could be removed via the cockpit locker for cleaning if required.
Touch wood, I have had no problems in the last 10 years. But you need to keep it topped up otherwise condensation will collect. Don't know if a plastic tank is any different with this problem.
 
I have two diesel mild steel tanks, both original as old as the boat (1971). Two years ago, one of the tanks started to leak from one of the corners at the bottom of the tank. I repaired it with epoxy and cloth, no problems since; the other tank still goes strong. So the answer to the question is that they last for very long time and they can be repaired.
 
Ruffles said:
No cheaper than a plastic tank. But I suspect there's a longer lead time.
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I did not bother getting quote for a new steel tank as it would have been impossible to fit without removing the engine. I replaced with a 91 litre Vetus plastic tank which gives me over 20 hrs motoring. I removed the old tankby cutting it into three pieces, rotating it as necessary(rope around tank and suspended from boom). I gained a lot of space and fitted the calorfier beside the new tank thereby gaining a locker in the galley. Boat is a Moody 33.
 
to be honest most workshops that can weld mild steel can weld stainless steal, i have a stainless tank in my boat its very little maintenance, made of 316 steel. but i think the way forward is the plastic type tanks. but its all down to how much you have budgeted for a tank. good luck with your choice.
 
Mine were 30 years old when I sold the boat, with not the slightest trace of corrosion. Paint the outside every 10 years or so, and keep the inside full when laying up.
 
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