Best material for fuel tank

[Wansworth]

We've gone in little more than a couple of generations from having a motor being considered a luxury, to fully accessible fuel tanks with drain sumps being considered highly desirable.

I can definitely see the advantage, but seriously there are zillions of boats out there without, mostly having no serious problems. It ain't a reason not to buy a second-hand boat.

For manufacturers (except at the money-no-object end of the market) providing such tanks as standard is one of very many 'nice-to-haves' that taken together would significantly increase the cost of the boat, which in turn would reduce sales, and hence viability and profits.

Not being a boat engine whizz I sort of fixate on what could go wrong if the engine stops so anyway I can improve the chances of it not stopping are a bonus!In my quest as a oap fora sailing boat with an engine of the half dozen I have seen only one had provision and that had narrow side decks

 

[LittleSister]

Nice to see that clever design on your boat.
I suspect it is not more common to have built in tanks due to cost. It's labour intensive, but done well, it makes a fantastic tank with little to go wrong. The access lids on our tanks are huge. They are secured on cork/rubber gaskets. The lids themselves are moulded such that they are raised in centre giving them lots of strength and rigidity. They are 10mm thick solid grp and fixed down with a ring of 10mm bolts glassed in on the underside of the tank.

Sadly, the fuel tank does not have great accessibility for inspection and cleaning. There is a small plate in the top of the tank with the pipes for fuel supply for motor and heater, return from the motor, plus fuel gauge, but it remains to be seen whether I can get my arm through the opening under that plate, and even if I can, I doubt I will be able to reach the whole length and depth of the rather big tank, but the deepest part (the forward inner 'corner'), where any water and most of the debris will collect, should be reachable with tubing at least.

The 'matching' water tank on the other side of the boat has a larger inspection plate, maybe about 8" x 10" - a rather quaint white enamelled lipped plate, sitting on a rubber seal on the also lipped opening - but it is still quite hard to reach the whole of the whole of the long tank from that to scrub it out. On that tank the outlet, and openings for the water level sight-gauge, are in the vertical inner wall (engine compartment bulkhead).

 

[LittleSister]

Not being a boat engine whizz I sort of fixate on what could go wrong if the engine stops so anyway I can improve the chances of it not stopping are a bonus!In my quest as a oap fora sailing boat with an engine of the half dozen I have seen only one had provision and that had narrow side decks

There is no perfect boat (and if there were you couldn't afford it!).

If only one had an alternative system available to propel the boat should the engine fail.

 

[Wansworth]

There is no perfect boat (and if there were you couldn't afford it!).

If only one had an alternative system available to propel the boat should the engine fail.

That’s an idea

 

[LittleSister]

Not being a boat engine whizz I sort of fixate on what could go wrong if the engine stops so anyway I can improve the chances of it not stopping are a bonus!In my quest as a oap fora sailing boat with an engine of the half dozen I have seen only one had provision and that had narrow side decks

It should be fairly easy to permanently rig up a small 'emergency' fuel tank with its own fuel filter, and a simple 2-way tap to switch to this from main tank and filter so in the event that -
- your engine stopped due to muck from your less than ideal main tank, and
- you were about to be swept onto the adjacent rocks by the tide/current and dashed to pieces, and
- you'd lost your anchor, and
- it was a flat calm so sails were no help or you'd put yourself too close to a lee shore and the wind had then piped up to prevent you clawing off it.

This small 'emergency' tank could be filled separately, or for the ultimate in sophistication it could be filled and permanently replenished by the return from the engine, and therefore always be full of only freshly polished fuel.

 

[Wansworth]

It should be fairly easy to permanently rig up a small 'emergency' fuel tank with its own fuel filter, and a simple 2-way tap to switch to this from main tank and filter so in the event that -
- your engine stopped due to muck from your less than ideal main tank, and
- you were about to be swept onto the adjacent rocks by the tide/current and dashed to pieces, and
- you'd lost your anchor, and
- it was a flat calm so sails were no help or you'd put yourself too close to a lee shore and the wind had then piped up to prevent you clawing off it.

This small 'emergency' tank could be filled separately, or for the ultimate in sophistication it could be filled and permanently replenished by the return from the engine, and therefore always be full of only freshly polished fuel.

Yet even more horrific scenarios

 

[Refueler]

Simples, it went off at a tangent. The OP was talking about condensation in metal tanks not the fuel bug.

As you well know - this aspect always comes up in Bug threads .. so a little pre-empting ...

 

[[70521]]

As you well know - this aspect always comes up in Bug threads .. so a little pre-empting ...

Ha ha...

Still interesting to read that there is little evidence for large lungfulls of air going in an out of any fuel tanks, just poor caps and crappy fuel.

I must look at moving the filler cap to somewhere more protected than the transom end of the deck with all that fresh and salt water wooshing past it.

 

[Refueler]

Yes, in addition to the one mentioned in another post, a US tester known as Maine Sail has had a metal tank set up ashore in very changeable weather, well below zero in winter, hot in summer, for 13 years (last time I looked). Not a single drop of water has been collected in all that time.

Fine - but if the tank is clean - totally empty with nothing in it ... with only venting. Its unlikely to have water stay ... with such changes - the water as probably moist vapour would return to the air ....

But throw a few grains of dust in there and you will get similar to what happens in the air above the earth - rain drops coalesce onto specks of dust ... and they stay as water drops.
Fuel in the tank - even just a small amount would have similar effect.

 

[geem]

Yes, in addition to the one mentioned in another post, a US tester known as Maine Sail has had a metal tank set up ashore in very changeable weather, well below zero in winter, hot in summer, for 13 years (last time I looked). Not a single drop of water has been collected in all that time.

I just look up that test. He had an empty tank! Why would he expect it to absorb water? Add in the mass of fuel to a half empty tank and it changes everything. Once water gets into the tank it drops to the bottom and is stopped from evaporating by the oil above.

 

[vyv_cox]

Was the tank full of fuel, half full or empty? It would be good to know more detail. Once water enters a tank with diesel in it. It will sink below the diesel so it can't evaporate. Its a trick used in commercial feed and expansion tanks where it is not possible to have a constant supply of make up water available to maintain the level. You add oil to the water and it sits on top of the water stopping evaporation.

The tank is ashore but set up exactly as if it was in a boat. It is empty and has been bone dry throughout. Link here Does an Empty Marine Fuel Tank Condensate? - Marine How To

 

[vyv_cox]

I just look up that test. He had an empty tank! Why would he expect it to absorb water? Add in the mass of fuel to a half empty tank and it changes everything. Once water gets into the tank it drops to the bottom and is stopped from evaporating by the oil above.

Why would water that condenses on the walls of the tank be re-absorbed into the air at typical winter temperatures? The theory as I understand it is that the tank and air warm in the day, expelling some air. At night it all cools, some air containing water vapour is drawn back into the tank, the water condenses and runs to the bottom. Next day same again. What is the mechanism for water to be re-absorbed into the air? I could leave a bucket with an inch of water in it outside all winter and it would remain exactly as I left it.

I have been leaving my tank as it finished the season for very many years.
Empty, full, half full and everywhere in between. I did drain the tank at about 30 years old and found a tiny amount of water there. It might have been there when I bought the boat, at 10 years!

If people are really concerned that condensation is an issue the remedy is simple. At the end of the season disconnect the vent hose from the external fitting and tape a partially inflated plastic bag over the end. No air or moisture can then enter and the bag takes care of expansion and contractions.

 

[geem]

Why would water that condenses on the walls of the tank be re-absorbed into the air at typical winter temperatures? The theory as I understand it is that the tank and air warm in the day, expelling some air. At night it all cools, some air containing water vapour is drawn back into the tank, the water condenses and runs to the bottom. Next day same again. What is the mechanism for water to be re-absorbed into the air? I could leave a bucket with an inch of water in it outside all winter and it would remain exactly as I left it.

I have been leaving my tank as it finished the season for very many years.
Empty, full, half full and everywhere in between. I did drain the tank at about 30 years old and found a tiny amount of water there. It might have been there when I bought the boat, at 10 years!

If people are really concerned that condensation is an issue the remedy is simple. At the end of the season disconnect the vent hose from the external fitting and tape a partially inflated plastic bag over the end. No air or moisture can then enter and the bag takes care of expansion and contractions.

If the tank cools and sucks in air then at some point it expells air. The tank needs to be colder than the air to create condensation. If the tank is the same temperature as the air, it won't condense. Leaving a dry tank in a barn at the same temperature as the air in the barn won't cause condensation. The tank will also have little mass so it will change temperature with the air. If the tank was a solid lump of metal, there are time when it would be far cooler than the surrounding air and condensation would occur. If you leave a ta k half full of fuel then the combined mass of the fuel and the tank could allow the tank to be cooler than the air. This would create a surface for condensation. You see this on uninsulated water tanks in buildings.

 

[[70521]]

If people are really concerned that condensation is an issue the remedy is simple. At the end of the season disconnect the vent hose from the external fitting and tape a partially inflated plastic bag over the end. No air or moisture can then enter and the bag takes care of expansion and contractions.

Perhaps a vacuum in the tank for those living in high latitudes.

 

[Refueler]

Oh Vyv .... You surprise me with this :

"Why would water that condenses on the walls of the tank be re-absorbed into the air at typical winter temperatures? The theory as I understand it is that the tank and air warm in the day, expelling some air. At night it all cools, some air containing water vapour is drawn back into the tank, the water condenses and runs to the bottom. Next day same again. What is the mechanism for water to be re-absorbed into the air? I could leave a bucket with an inch of water in it outside all winter and it would remain exactly as I left it."

An empty tank that can vent freely will stay near dry, as long as venting is sufficient to allow large volume change quickly ... .
But restrict that venting as most tanks are by design ... have changes of temperature of the air surrounding allied to the cooling / warming of the tank itself ... then you have a working condensing / vapourising machine.
The tank will because of its material will warm slower than the air surrounding it ... similarly in cooling.

The intake and extake of air from the tank will be experiencing different temps inside tank / tank walls and outside. As long as tank is able to vent easily - this can be controlled - same as you opening hatches and venting your cabin. But restrict it and you get condensation.

Introduce a medium such as fuel - that water as another says will make its way under the fuel and then be basically trapped. If the fuel is ultra dry - unlikely as fuel stations are free air vented .. then the fuel would actually absorb a tiny % of the moisture as I explained earlier.

 

[B27]

If condensation is indeed a problem, are we correcting assuming that plastic will perform better in this regard?

 

[B27]

......

Introduce a medium such as fuel - that water as another says will make its way under the fuel and then be basically trapped. If the fuel is ultra dry - unlikely as fuel stations are free air vented .. then the fuel would actually absorb a tiny % of the moisture as I explained earlier.

Fuel stations in the UK probably are not free air vented.

AIUI, the requirement for something slightly more intelligent was part of the reason for the reduction in the number of small fuel stations in the UK.

 

[Refueler]

If condensation is indeed a problem, are we correcting assuming that plastic will perform better in this regard?

Why ?

Unless temp coefficient is an issue.

 

[Refueler]

Fuel stations in the UK probably are not free air vented.

AIUI, the requirement for something slightly more intelligent was part of the reason for the reduction in the number of small fuel stations in the UK.

TBH - I cannot answer that one as I do not follow UK Petrol Station Regs ... but last visit - I only saw the same flame resistant vents ...

Usual alternative to air blanket is Nitrogen ..... I don't recall seeing any Nitrogen generators or tanks .................

The supply road tankers are air blanket ... storage tanks are air blanket ..... ????

 

[bluerm166]

Recently looked at a replacement diesel tank after contamination in present s/s tank.
Tek Tanks stress the need for a fire wall between their tanks and the engine compartment for all their plastic ranges .
This certainly could not be achieved on our boat and probably not on your typical older sailing yacht without extreme upheaval and probably only sensibly achievable if the original design covers the requirement .