Diesel question: keep it topped off or let it go down?

[Dsanduril]

If you don't sail like the Pardeys, and actually have an engine then the math to me works more like this - do you have enough fuel to get back to a nice, snug anchorage from the furthest part of your sail? Crossing oceans in a typical auxiliary sailboat this doesn't mean much, but for a summer coastal sailor I'd base my fuel storage on getting to the furthest point I usually sail, losing the mast, and being able to get back to someplace secure against strong wind and crappy seas (you did just lose the mast after all). Being able to jury-rig/fix things is great, but having the engine option in that moment is also of value (to me anyway).

[Paul L]

Originally Posted by sailorboy1

There are emergency diesel generations in millions of buildings around the world. Most places run the generators once in a while, but I bet it is a very very very rare place that just replaces the diesel due to age.

But I'm not to argue the point beyond this.

Interesting point. A little Google searching brought up this article on fuel for emergency gensets. It notes

Aboveground: The heat from the sun will cause the fuel inside the tank to expand and contract on a daily basis. This daily contraction will also lead to condensation forming on the walls of the tank and settling to the bottom and again providing a growth medium.

And says to test the fuel annually.
http://www.asne.com/the-importance-o...by-generators/

[Jim Cate]

Aboveground: The heat from the sun will cause the fuel inside the tank to expand and contract on a daily basis. This daily contraction will also lead to condensation forming on the walls of the tank and settling to the bottom and again providing a growth medium.

Please note the initial phrase in the quotation: "Above ground".

This is rather different than our tanks which are supported in an infinite heat sink of generally coolish water. The constant temperature bath pretty well eliminates the diurnal temperature variation which is posited as the source of "condensation" in the storage tank.

As others have previously noted, "condensation" has pretty well been ruled out as a significant contributor to tank contamination.

As to diesel just decaying from age... you would think that BP would know best, but there is so much apocryphal evidence of it being useful for many years or even decades that one must wonder. I've certainly used diesel that was several years old with no noticeable issues... filter clogging or stoppage as they suggest will happen. Maybe new diesel has changed in its properties??

Jim

[barnakiel]

We normally try to run the tank almost empty once in a while. Then refill with fresh fuel. Our case is we only either sail or not, so our diesel gets nearly 3 years old in between.

I think any boat used on regular basis just fills up and goes and that's that.

This much said, how often do you completely clean and inspect your tank. We do this every 5 years.

Never found any dirt inside. Hence our method must be OK for how we use our boat.

Cheers,
b.

[Paul L]

Originally Posted by Jim Cate

Please note the initial phrase in the quotation: "Above ground".

This is rather different than our tanks which are supported in an infinite heat sink of generally coolish water. The constant temperature bath pretty well eliminates the diurnal temperature variation which is posited as the source of "condensation" in the storage tank.

......

My boat is currently stored on the hard with tanks full. The tanks go through some thermal cycling daily. So far I've not a problem with diesel up to a year old and probably older.

[Wotname]

Originally Posted by Jim Cate

Please note the initial phrase in the quotation: "Above ground".

This is rather different than our tanks which are supported in an infinite heat sink of generally coolish water. The constant temperature bath pretty well eliminates the diurnal temperature variation which is posited as the source of "condensation" in the storage tank.

As others have previously noted, "condensation" has pretty well been ruled out as a significant contributor to tank contamination.

As to diesel just decaying from age... you would think that BP would know best, but there is so much apocryphal evidence of it being useful for many years or even decades that one must wonder. I've certainly used diesel that was several years old with no noticeable issues... filter clogging or stoppage as they suggest will happen. Maybe new diesel has changed in its properties??

Jim

Yep, you would like to think that BP should know but then again, you gotta remember they do have vested interests (and a poor track record e.g. the Deepwater Horizon).

I can attest to the "zero condensation in boat tanks" line of thought.

As a personal test, I left my 25l boat tank completely full over winter and and collected the free water from the tank in late spring. The next year at the same location and same period of time, I left the tank almost empty. In both cases the amount of water was very small, a few ml, (less than a teaspoon).

For other readers, winters here are cool and damp (Jim knows this which is why he isn't here )

[daletournier]

When I purchased my boat one tank had five year old fuel they picked up in Fiji, the boat had hardly been used since. I had no problem.

[Jim Cate]

For other readers, winters here are cool and damp (Jim knows this which is why he isn't here )

Once again, Wottie shows how astute he is!(LOL).

Jim

[Pelagic]

There was a very good thread around 2 years ago about Diesel Fuel, treatment, polishing and storage.

Two contributors were petrochemical engineers and one specifically was doing studies /tests on storage issues for biofuel.
This apparently has been causing problems at the large storage facilities because biodiesel absorbs moisture in the air....
Recommendation was to close fuel tank air vents when not in use, which is what I do now..

Also if she happened to.sink at the dock, no fuel should leak out!

[Milko Berben]

As far as I know in Holland standby emergency generators have very little fuel in the tank maybe 200 liter or so in case of emergency the truck will come directly and bring the big bulk at least at master card it was like that.

[Pete7]

Originally Posted by Dockhead

There is still controversy on this question, but there is a lot of evidence that condensation inside diesel fuel tanks of boats does not occur in any significant quantities, and that condensation as a major cause of water in fuel tanks is a myth. Our own MaineSail actually did some experiments to back this up.

This was the one article he produced that I have a problem with. He chose to put a sealed tank (I think an outboard 25 litre type) inside an unheated shed over the winter with a tube going outside, the shed representing a boat hull. The sealed tank was empty and he recorded no build up of water during the winter. Now the idea is that temperature and air pressure changes will cause water vapour to be drawn into the tank I think is flaws because a clean sealed tank will quickly change temperature to the prevailing conditions. However, if the tank was half full of diesel then the time it would take to change temperature is much longer. So I personally still think a tank will absorb water over a period of time. That said it will be nothing in comparison to a leaking deck filler with a perished o ring.

Originally Posted by Dockhead

So I don't think it's a good idea to keep a lot of diesel fuel in the tanks getting old while not being used up. I leave my tank mostly empty over the winter. But the OP was not asking about that - - he was asking whether during the course of an active summer's sailing whether he should keep the tank higher rather than lower. That's a rather different question.

I have noticed a lack of petrol stations at sea, so it would be prudent to keep the tank topped up and a spare can with spare piping also available, just in case.

BTW, There might be a a fishing fleet refueling ship somewhere to the East of Greenland. I have been trying to Google it without much luck, but previous explorers have mentioned it. Alan Priddy on his first Atlantic crossing lamented not knowing it was there as he ran out of fuel 350 miles to the West of Iceland in an open rib.

[Dockhead]

Originally Posted by Pete7

This was the one article he produced that I have a problem with. He chose to put a sealed tank (I think an outboard 25 litre type) inside an unheated shed over the winter with a tube going outside, the shed representing a boat hull. The sealed tank was empty and he recorded no build up of water during the winter. Now the idea is that temperature and air pressure changes will cause water vapour to be drawn into the tank I think is flaws because a clean sealed tank will quickly change temperature to the prevailing conditions. However, if the tank was half full of diesel then the time it would take to change temperature is much longer. So I personally still think a tank will absorb water over a period of time. That said it will be nothing in comparison to a leaking deck filler with a perished o ring.. . .

Well, diesel fuel does absorb water to some degree, and will reach saturation eventually if it is in contact with air. If the temperature then goes down water will precipitate out. Maybe it makes sense to block the vent during long storage to reduce this effect. But that's not the mechanism which is the subject of the condensation myth -- that's the idea that empty space in the tank should be avoided because the tank will breath in moist air and water will condense out of it. This is manifestly wrong for several different reasons -- first of all, the temperature outside may change, but the temperature of sailboat tanks is quite constant. Furthermore, any warming of the tank during the day which does occur, if it occurs at all, will cause the tank to breath OUT, not IN. You need to bring WARM moist air in contact with something COLD to cause condensation -- it can't happen with a tank the way people imagine it. Breathing in cold air at night, even saturated cold air, which will then get warmed up in the day time, cannot cause condensation. And that's even if any "breathing" does occur, which will not for most boats, certainly not mine -- I've measured the temperature of my tank, and it does not change between day and night at all, not even a tenth of a degree.

So in my opinion this is a total myth with no substance at all behind it. People get water in the fuel -- mostly from bad o-rings on deck fills (work of the devil -- diesel tank fills should never be at deck level) -- and have to think of SOME explanation for how it got there, and dream up these myths, just like ancient people trying to figure out the cause of lunar eclipses.

Oh, and by the way -- my diesel fill is a meter higher than the deck, protected in the deck house, with a proper spring cap. I inspect my tank every year and have never found a single drop of water in it, over 9 years of keeping her in this extremely wet climate of Southern England. With mostly empty tank in the winter. Coincidence? Well, it's just one data point.

[Pete7]

Ah, but your yacht like mine lives in the water all year round. For the thousands of yachts in the UK which are lifted out each winter then temperature and air pressure changes occur daily. Warm air drawn into a cold tank condensates on the tank walls. However, as you said it's the filler which is the main culprit.

Interestingly the coding for a UK charter boat requires the vent and fill hoses to be fitted with a valves capable of sealing off the tank.

Pete

[Dockhead]

Originally Posted by Pete7

Ah, but your yacht like mine lives in the water all year round. For the thousands of yachts in the UK which are lifted out each winter then temperature and air pressure changes occur daily. Warm air drawn into a cold tank condensates on the tank walls. . .

Sure but how in the world will warm air be drawn into a cold tank?? Think about it! A cold tank in the day time breathes out, not in! Whenever the tank is colder than the outside air, it will be breathing OUT! As it cools off and breathes IN, it will always be warmer, not colder, than the outside air, otherwise how in the world could it breathe IN? Condensation cannot happen in this way.

[rourkeh]

David Pascoe on this issue.
" For one thing, you do not want to keep fuel in the tanks for too long because of bacteria build up, among other problems. You must have water separating filters with sight bowl so that you can monitor water and debris accumulation before fuel system failure occurs due to clogged filters.

It's best to draw down both tanks equally even if you only fill up half-way. Water will accumulate more rapidly when tanks are maintained full or near full. Yes, you read that correctly -- this is due to the lack of agitation that is much more pronounced when fuel levels are lower. This, in turn, results in scavenging water and debris from the bottom which is then removed by the filters. If you’re not using much fuel, it's better to maintain the tanks at half level so that you’ll refuel more often and keep it fresh. Most water comes either from the fuel suppliers tanks or leaking deck fills. Note here that many deck fills are going to leak a little. We’re talking a matter of droplet size amounts here, but they do add up over time. If you are getting water, check the O-ring on the cap, make sure it's there and not damaged. Many caps simply don’t have an O-ring seal and rely entirely on the threads to keep water out."