Diesel tank leaking ( it's not, but what's the chances?)

Thepipdoc

Thepipdoc

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I often read about boats being ruined by leakage of diesel ( there's an active thread on here at the moment), and it concerns me that whilst it might not happen every day it's a fairly common occurrence. The biggest issue seems to be tanks that split at the seams, and as a result have to be removed.
The thought of having to remove a tank of any sort from my boat (Sealine F43, 12 years old.) sends shudders through me. A diesel tank would probably mean huge amounts of the boat would have to be cut out! :(
What's the likelihood of stainless steel diesel tank having to be removed and what's the general cause of tanks splitting
 
poor seam welding

panting of the panels due to lack of internal structure/baffles and fuel movement, leading to work hardening of the weld area

improperly designed support

external impact or overloading from other equipment stored on the tank, and possibly concomitant electrolytic issues

EDIT
internal corrosion from water ingress / contaminated fuel / condensation, and dirty tanks not cleaned out regularly)
 
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I have worried about the same thing but i guess its a bit like worrying about being mugged after watching a crime watch programme.
Thousands out there but you only get to hear of the unfortunate instances.
 
It does happen but not that frequently;

My old boat had steel tanks 16 years old they had rusted through on the top from seawater coming in engine room bvents and sitting on top of tanks.

I saw a Uk production boat with aluminium tanks rot through the bottom due to water in the tank and fuel bug, waste products attack the aluminium.

Stainless steel tanks sometimes split due to being too thin and work hardening.
 
Thepipdoc said:
I often read about boats being ruined by leakage of diesel ( there's an active thread on here at the moment), and it concerns me that whilst it might not happen every day it's a fairly common occurrence. The biggest issue seems to be tanks that split at the seams, and as a result have to be removed.
The thought of having to remove a tank of any sort from my boat (Sealine F43, 12 years old.) sends shudders through me. A diesel tank would probably mean huge amounts of the boat would have to be cut out! :(
What's the likelihood of stainless steel diesel tank having to be removed and what's the general cause of tanks splitting
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Chances of a steel tank needing replacement before 30 years is slim.

Chances of aluminium needing replacement after 5 years is high if the bilge water has been allowed to touch the tank for any length of time (electrolysis causes pitting).

Chances of a stainless tank needing replacement after day 1 is very high if the boat has been transported by road above 1/4 full.
or if a fast boat and used in a heavy sea.

Stainless is too rigid and has no tolerance for any flex endured of either the boat or tank as the contents slosh around, baffles help but do not solve the problem.

Surely your sealine hasn't got stainless tanks ?

I would have thought mild steel but at worst Aluminium.
In a flybridge the chances of bilge water touching the tank are remote, you shouldnt have an issue.

The problem is with sports boats where the tank is in the V and 2to3 gallons of bilge water is enough to cause serious damage.
 
Relatively, the F43 isn't too bad. You do have to remove a fair amount of the internal furniture, but there is ultimately a wooden floor above the tanks that can be removed and the tanks lifted vertically. A forum member around here had them done in his F43 (well, a previous owner did) and on the Sealine it's not the end of the world...

My Princess is not so easy, as the floor above them is part of the superstructure moulding - in the vein of a Haynes manual.. Step one: remove engines. See section 'x'.
 
DAKA said:
Chances of a steel tank needing replacement before 30 years is slim.

Chances of aluminium needing replacement after 5 years is high if the bilge water has been allowed to touch the tank for any length of time (electrolysis causes pitting).

Chances of a stainless tank needing replacement after day 1 is very high if the boat has been transported by road above 1/4 full.
or if a fast boat and used in a heavy sea.

Stainless is too rigid and has no tolerance for any flex endured of either the boat or tank as the contents slosh around, baffles help but do not solve the problem.

Surely your sealine hasn't got stainless tanks ?

I would have thought mild steel but at worst Aluminium.
In a flybridge the chances of bilge water touching the tank are remote, you shouldnt have an issue.

The problem is with sports boats where the tank is in the V and 2to3 gallons of bilge water is enough to cause serious damage.
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Our similar aged Sealine (S23) has got a stainless fuel tank......
 
Our back tank started leaking, it got so bad that we were pumping fresh diesel out the bilges. We bit the bullet and tore up the cockpit deck, and pulled it out, after we had emptied it. On inspection we found 6 stress cracks running across the whole width of it 6'x 4'x 15". all the welds were good, so we had a specialist firm tack the cracks and a whole new bottom skin welded on. The cause we were sure was that the tank had been sitting on top the p bracket studs, no insulation! It went back sitting on a bed of conveyor belt rubber. Should have said they are stainless, and that material work hardens so it's good to insulate them from vibration.
 
An aluminium tank with the fuel bug and water in the bottom will get corrosive due to fuel bug excreta and this will east through the tank from the inside.
 
DJ43 on here has first hand experience of replacing the tanks on an F43.
Major job by all accounts, involving stripping out a lot of the interior.

I know he believes the leaks started by fuel sloshing around in big seas off the east coast.

I'm sure he will be along soon to share the story..
 
SpottyDog5 said:
DJ43 on here has first hand experience of replacing the tanks on an F43.
Major job by all accounts, involving stripping out a lot of the interior.

I know he believes the leaks started by fuel sloshing around in big seas off the east coast.

I'm sure he will be along soon to share the story..
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We had to change our tanks on our F43 as per spottydogs post,yes we had been caught out in some big seas,both tanks went within 7days of each other,when tanks were removed(by me as unable to find anyone who had done a f43 before)they had been made out of aluminium and were larger than the standard size,problem was the baffles were too far apart,had new ones made with extra baffles,all in all not an easy job, one of the hardest jobs is removing the fixed furniture,when thats removed floor comes up and cross bearers removed,tanks can be lifted out,
 
The replies are interseting and I certainly don't ever want to put some of the advice into practice. Like I said, the tanks aren't leaking, they are perfectly sound:):). l was just curious why so many leak, but as someone already pointed out, it's quite rare and we only hear of the ones that do leak, and never the ones that don't.
 
omega2 said:
It went back sitting on a bed of conveyor belt rubber. Should have said they are stainless, and that material work hardens so it's good to insulate them from vibration.
Click to expand...

Not applicable in your case but worth a mention I think, rubber contains carbon which is cathodic to aluminium, sitting an aluminium tank on a sheet of rubber is a recipe for disaster.

Aluminium and stainless both require a supply of oxygen to keep up their corrosion inhibiting properties. Ideally a tank would be designed and built so that it has an air gap all round inc underneath and is supported in such a way as to minimise the surface area that is airless. Mounting on moisture retentive materials eg wood, foam etc doesn't help either.
 
I have had no diesel bug or tank corrosion issues, at least not as far as I am aware.
But I have started using a fuel additive this year. I chose Marine 16 Diesel Fuel Complete as it cleans and lubricates the fuel sytem as well as protecting against the bug.

http://www.marine16.co.uk/acatalog/Fuel_Treatment_Products.html

I have no connection with Marine 16. There are of course several other manufacturers of fuel treatments.

I had not thought of the tank corrosion issue due to diesel bug but it seems another good reason to use a fuel treatment.
 
JSYmartini said:
Not applicable in your case but worth a mention I think, rubber contains carbon which is cathodic to aluminium, sitting an aluminium tank on a sheet of rubber is a recipe for disaster.

Aluminium and stainless both require a supply of oxygen to keep up their corrosion inhibiting properties. Ideally a tank would be designed and built so that it has an air gap all round inc underneath and is supported in such a way as to minimise the surface area that is airless. Mounting on moisture retentive materials eg wood, foam etc doesn't help either.
Click to expand...

We had to replace an aluminium tank in our s240 some years back when it failed due to corrosion, when lifted it had been bedded on strips of foam rubber, at the points where the tank had been in contact their was a lot more corrosion than the parts that were exposed so your sugestion that the air helps maintain the corrosion ressistance is true.

The tank was 12 years old when it sprung a leak, built by the Tank co, who did all the tankage for sealine back in the 90's.
 
Our Princess 41 had a leak in one of the mild steel fuel tanks due to excessive rusting on the top and sides. There were signs of internal rusting as well as the fuel filters kept becoming clogged with similar debris. I had to bite the bullet, remove both engines (through the flybridge floor) followed by the offending fuel tanks. I was advised (and complied) by a tank maker to replace them with stainless steel to prevent a repeat performance. Seeing Daka's post has given me concerns as I usually find him to be incredibly knowledgeable. Having said that I have had no further issues since and I did have the opportunity to clean the entire engine room, repaint it and fit all new fuel pipes, taps and filter units. None of this will make me feel any better if the tanks start to leak again. I would rather sink the boat than go through the same rigmarole again. It was an extremely expensive operation incorporating the use of a crane with all the associated dangers.
 
I would never spec a stainless steel tank and I am totally gob smacked that sealine appear to have fitted some, I assume they are either, after market, special request or perhaps aluminium mistaken for stainless :confused:.

That said I wouldnt worry in your position unless your Princess is over powered and you intend smashing through waves @ 30knots.

I would avoid road transport at all costs.

If you ever do road transport then empty your tank (not that easy).

Never lift out on soft ground .
It will last for years :)
 
There's absolutely nothing wrong with stainless tanks, they just need to be designed, built and installed correctly, as with any other type of tank.

My rib has stainless tanks as spec'd by the MOD. Now 18 years old, when in service she was "air deployable" yet they're still in perfect condition.
 
I have no idea how big your rib tankage is, I suspect smallish in which case agreed a smallish box shouldnt have to endure much flex.

A tank in an F43 will be 100-150 gallon, possibly an odd shape to fit the hull .

If road transported 1/2 full it will rupture the first time the lorry driver bounces a curve.
 
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