Laying up

[chrisclin]

It's getting to that time again. I've just booked a date for my boat lift at the beginning of next month.
I'm wondering what I do about my fuel tank which currently has about 20 litres of red diesel.
In the past I've topped up my tank for the winter to avoid condensation. However, I gather opinions may have changed. What are the views of the panel as to whether I top up or leave the tank as empty as possible?

 

[Tranona]

Never bothered with doing anything. Once laid up a boat for 9 years and although I extracted the diesel and replaced, it was clear with no signs of water or gunge. If you have any doubts, use a Pela to extract some fuel from the lowest part of the tank and if it is clear you should have nothing to worry about.

 

[Stemar]

Yes, but that diesel didn't have fame in it, which has a negative effect on storage life.

All the same, I think I'm probably going to top off my tanks, since they're half full and I've no sensible way of disposing of the fuel, as I understand Ms Truss would take a dim view of me putting it in my car. Keep it with a minimum of air and condensation, and it should survive the winter.

 

[johnalison]

In the past I have topped up my tank, according to custom, but my use has been so little in recent years that I risk having fuel lying around for years. My tank holds 145l, which has been advantageous in the past but is more than I need with local sailing. I had to put some fuel in the other day but limited myself to about half a tank. I always include a bio-additive. So far this seems to have kept me trouble-free but I'm not fully convinced and will continue to be cautious.

 

[Tranona]

Yes, but that diesel didn't have fame in it, which has a negative effect on storage life.

But it is not the storage life that is the concern over a winter, but condensation leading to water in the fuel - which I suspect is overrated. Filling the tank actual increases the time the fuel is in the tank so maybe running close to empty at the end of the season and putting new fuel in at the beginning is a better strategy!

 

[Mudisox]

Top up , good excuse to cross the channel to Guernsey/Jersey.

 

[vyv_cox]

I just returned to my boat after a three year absence. My 100 litre tank was left 3/4 full but I know the filler does not leak and the condensation theory is a myth. I sampled with a Pela and found no.problems, then started the engine, which fired up after about 15 seconds. Seems to be running fine.

This is in Greece, where road fuel is mostly delivered by mini-tankers that have a fairly rapid turnover. I would be a lot more concerned if I was buying from marina bunkers, especially floating ones.

 

[Stemar]

I would be a lot more concerned if I was buying from marina bunkers, especially floating ones.

Certainly in areas where turnover is likely to be low, but I reckon places like Premier in Portsmouth must have a pretty good turnover.

 

[dunedin]

I tend to believe Vyv's view that "the condensation theory is a myth", but it is certainly not a myth that recent diesel tends to have a higher biofuel content. Some marina pumps suggest they have no bio-fuel, but others on here have suggested that may be wishful thinking based upon industry rules.
I have therefore switched from the "fill up at end of season" to the "fill up at starts of season" - with an important caveat. I try to avoid low volume diesel suppliers in early season in case their diesel has lain in their tanks since the previous summer - a busy marina (with lots of large motor yachts !) or a fishing harbour will have faster turnover.

 

[doug748]

It's getting to that time again. I've just booked a date for my boat lift at the beginning of next month.
I'm wondering what I do about my fuel tank which currently has about 20 litres of red diesel.
In the past I've topped up my tank for the winter to avoid condensation. However, I gather opinions may have changed. What are the views of the panel as to whether I top up or leave the tank as empty as possible?

I would top up now, it's always nice to feel one job out is of the way and start the new season ready to go.

Plus, by spring you may not be able to afford it ?


.

 

[Graham376]

We're running on 4-5 years old road diesel at the moment with no problems on 8 hours trip on motor last week. I always dose with Fuel Set when filling - Fuel Set | Liquid Engineering UK Ltd - whether it's better or worse than other products I don't know.

 

[jdc]

I tend to believe Vyv's view that "the condensation theory is a myth", but it is certainly not a myth that recent diesel tends to have a higher biofuel content. ...

But it could be a myth that biofuel is bad.

My one - and so hardly conclusive - data point is that I opened the diesel tanks on two boats of almost identical age (13 years) and size. One, mine, kept in the UK, had been only ever filled with red marine FAME-free diesel and the other one, my brother's, had been kept in Greece and had only ever been filled with road fuel containing 5% FAME. The UK based boat's tank was coated with a black tarry substance whereas the Greek boat has absolutely spotless tanks, really mirror clean.

Differences / possible explanations:
1. The UK based boat had been used quite a bit more so its fuel had been standing less long (but you'd think this would make for cleaner tanks)
2. The UK boat had had a lot more fuel throughput.
3. The Greek boat had been kept at a higher ambient temperature, in a less humid atmosphere (Athens vs Cornwall).
4. FAME is a good solvent and had dissolved the tarry (asphaltene I surmise) deposits? Otherwise I'm a a loss to explain it.

I suspect that there are a lot of myths about fuel!

 

[LadyInBed]

As Vyv, my tank sat unused for two years but only a quarter full (50 ltrs), the engine fired up this year no problem and no condensation.

 

[thinwater]

... and the condensation theory is a myth. ...

As a refinery guy and long time tank inspector, this statement always makes me laugh. In fact, one of the significant hazards during the inspection of large tanks is falling rafters, damaged by condensation (so common it is mentioned in the code as a safety hazard). I've found rafters on the floor. The parts of the tank to corrode first are always the inside of the roof and the inside of the bottom, both from condensation. The inside of the roof is commonly dripping with condensation the morning, the drips fall through the diesel to the bottom, and from there they cannot evaporate again.

It is minor. The amount is small and it does not necessarily overrule the consideration of holding fuel for years (for those that do not cruise). If you really want dry fuel, either add a silica gel vent drier, or consider taping a loose sheet of poly over the vent (enough bulge in it so the tank can breath).

The usual source of water is leaks. That is really the concern.

There are those that believe that empty tanks not filling with condensation is proof that it does not happen. Unfortunately, this is a false analogy.

 

[vyv_cox]

Perhaps it's a matter of scale or size of vents. You may like to read this.

Does an Empty Marine Fuel Tank Condensate? - Marine How To

Even if yacht fuel tanks do attract atmospheric condensation, and my calculations say they don't, it is very easy to prevent. Remove the vent tube and tape a plastic bag over the free end. All air is now contained

 

[thinwater]

Perhaps it's a matter of scale or size of vents. You may like to read this.

Does an Empty Marine Fuel Tank Condensate? - Marine How To

Even if yacht fuel tanks do attract atmospheric condensation, and my calculations say they don't, it is very easy to prevent. Remove the vent tube and tape a plastic bag over the free end. All air is now contained

Marine How-To is a very smart boat guy. I am a 40-year refinery chemical engineer and 20 year tank inspector. I am quite sure of what I have seen, over and over, for 20 years. I've seen peoples calculations, and there are always minor but fatal flaws in reasoning. It's tricky to account for all of the factors. The ones they most often miss is that the steel plate roof gets cold at night, and that any condensation that forms falls into the fuel and is trapped under it.

Condensation varies a great deal with weather, the location of the tank, and ventilation of the boat. Less for bilge tanks, more for bridge deck tanks. It can be near zero in some cases and severe in others.

Tank roof underside condensation is in the inspection code. Is there more to say that that?

Yes, taping a loose bag over the vent is a perfect solution. Might as well cover the filler while you are at it... just in case (some are located in bad drainage paths--totally separate problem).

 

[vyv_cox]

Marine How-To is a very smart boat guy. I am a 40-year refinery chemical engineer and 20 year tank inspector. I am quite sure of what I have seen, over and over, for 20 years. I've seen peoples calculations, and there are always minor but fatal flaws in reasoning. It's tricky to account for all of the factors. The ones they most often miss is that the steel plate roof gets cold at night, and that any condensation that forms falls into the fuel and is trapped under it.

Condensation varies a great deal with weather, the location of the tank, and ventilation of the boat. Less for bilge tanks, more for bridge deck tanks. It can be near zero in some cases and severe in others.

Tank roof underside condensation is in the inspection code. Is there more to say that that?

Yes, taping a loose bag over the vent is a perfect solution. Might as well cover the filler while you are at it... just in case (some are located in bad drainage paths--totally separate problem).

But in a boat the tank roof is not exposed to the atmosphere. Even if it was, the condensation forms on the outside and cannot fall into the fuel. In my case it is beneath the coaming with the cockpit cover over that. In some cases it is deep inside the boat. Totally different situation from an outdoor storage tank.

 

[Marceline]

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 ?

 

[Stemar]

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.

 

[thinwater]

And I have seen condensation damamge on the inside of the roof of marine tanks.

Just sayin' there is a spectrum of situations and calling condensation a myth is false. Blaming most water problems on it is equally false--leaks are the common cause and the cause of ALL serious water problems.