Laying up

[jdc]

In the UK, the air is always damp - between 70 and 90% relative humidity, on a boat surrounded by water it's going to be at the high end. That damp air finds its way into your fuel tanks as you burn fuel. Then we have a cold spell, so some of that moisture condenses - a matter of simple physics - and gets into the fuel. It's likely that most of the time, it's so little, it gets through the injectors and out through the exhaust without causing a problem. Larger amounts - you burned the fuel in the summer and left that damp air in the nearly empty tank until winter - should be caught in the filter/water trap so, again, no problem. The only time you'll have a problem from water in the fuel is because you filled up at a dubious source and bought a significant amount of water at the price of diesel.

But - there's always a but - the interface between liquid water and fuel is a place some bugs like to hang out. Get too many of them and they'll build up over time. A bumpy trip and enough space in the tank for the fuel to slosh around can cause those bugs, or their corpses, to block your filter, which can spoil your day. A biocide will prevent that if used regularly. IIRC, Premier's fuel contains a biocide.

All that applies to pre-fame diesel. I don't know enough about it to say what other problems it may cause, but a Google suggests it exacerbates the above.

It's not sure that diesel with FAME exacerbates the problem of free water, it may even help. Water does get dissolved into diesel, albeit a minuscule proportion - around 50ppm. In FAME it is a much higher proportion, around 1500ppm.

So if 7% FAME that's 0.93 * 50 + 0.07 * 1500 = 151.5. So even if only 7% FAME, about 3 x more water (from condensation or elsewhere) will simply be 'mopped up' by the diesel. To put 151.5ppm into perspective, suppose you've 30 litres in the tank: 30 * 1000 * 151.5e-6 = 4.5ml: only about a teaspoon but could be sufficient to absorb condensation. Note that this assumption that the solubility of a mixture can be estimated by linear combination of the proportions of diesel and FAME is dubious, but unlikely to make significant difference for well stored and well blended fuel).

This assumes of course that you have acquired the diesel from a good supplier who has ensured that the fuel isn't already saturated with water (by EN590 it must contain less than 200ppm out of the ~1500 it can absorb ).

A guide to handling FAME can be found here. What it says about regular addition of biocides (it says not to do it) is interesting and is exactly the same advice as IAATA guidelines for aircraft fuel.

 

[Chiara’s slave]

I've a 20litre red plastic petrol tank for our 24' boat's outboard (its just over half full) - would I be ok storing that at home in the concrete garage ? or should I offer it to someone who's needing some car fuel (our car is electric) and buy some more next year just so the fuel isn't sat around for 6months ?

Ethanol mix petrol is quite hygroscopic. Add fuel treatment, close the vent, it will store ok for a winter. But if you can use it in a car, and get fresh in spring, even better.

 

[Marceline]

Thanks ever so much. Will see if there's any local services I can offer/donate it to for one of their vehicles

 

[thinwater]

...A guide to handling FAME can be found here. What it says about regular addition of biocides (it says not to do it) is interesting and is exactly the same advice as IAATA guidelines for aircraft fuel.

This thread is about lay-up, right? Unless you are going to test every 15 days and drain water every 7 days, it seems to recommend treating with Biobor JF. Unless I read your link wrong.

AMM recommended fueling practice for parked aircraft
Aircraft parked for longer than 1 month
• Fill each tank 10% of total volume while injecting
biocide as per OEM AMM
• Test each tank for microbial contamination at
start of parking and after 30 days
• If no biocide is applied testing needs to be done
every 15 day
Drain any free water from tank low points/drains,
every 15 days
• If no biocide was applied, drain any free water
from tank low points/drains, every 7 days

 

[jdc]

This thread is about lay-up, right? Unless you are going to test every 15 days and drain water every 7 days, it seems to recommend treating with Biobor JF. Unless I read your link wrong...

You're quite right this is about laying up, which I had maybe slightly lost touch with.

The reason I put in the link was to let others read what is said on storage of diesel and FAME, and encourage all to read the detail about dosing with biocide. To make a 'shock' dose with biocide may make sense on layup, but those who just put a bit in on every top-up throughout the sailing season are maybe not doing what's for the best.

We should perhaps start a new thread on the subject of when, and when not, to dose with biocide, and what types are acceptable and obtainable - do you want to lead off?

 

[thinwater]

^^ Good points.

The other question, I suppose, is that a great many use so little fuel, filling perhaps once per season, that lay-up and regular fueling aren't much different. The fuel they take on mid-summer will likely be the winter fuel. That is the reason for all the discussion of full vs. half empty and fresh fuel. For a regular cruiser, they will always have fresh fuel and may barely lay up. For an occasional local sailor, although they sail, the tank is basically "laid-up" for the life of the boat, with refueling every year or two. I've always tried to burn through the tank every 3-4 months at most, and far less in the summer.

No single answer.

 

[tillergirl]

There is another side of the coin to look at. Last winter I did not top up the tank because I intended to replace that gauge sender and I thought it might be better than when full. At the start of this season, immediately afloat and went over for fuel. Because of the rise of cost of fuel, it cost me £150 extra! No sign of condensation BUT the vent is inside so might be better than if externally.

 

[Biggles Wader]

I stay in all year round on the offchance of the odd winter sail so no lay up as such but the boat has long periods of non use. I leave as little fuel as possible in the tank always dosed up with marine 16 but I have a sump with a drain which I empty every spring just in case. That drain plug is so useful.