deisel tanks, fuel supply must be on top? is that right?

[GHA]

So, thinking more about a day tank, how easy would it be to install in, for instance, a cockpit side locker, or under an after deck? Filler, drain off and engine feed tap all to hand, and a good gravity feed, no bleeding of the pumped feed from the main tank needed.

I fitted one when putting in a new engine a couple of years ago - well worth the effort!

Was a bit of work but now can pump from main to day tank or form a canister to day tnk or the other way round.

Filtered clean fuel only goes to the day tank. With the fuel line coming from the bottom of the day tank then running out the top it still needs priming if you run it dry.

 

[rgarside]

Don't forget that the fuel supply line still goes to the bottom of the tank even though it exits through the top ..... so, as PVB says, the gravity head is the same as a bottom exit.

Richard

The difference is that if the connection of the pipe to the tank exit nozzle leaks, in the case of a bottom connection the tank will empty, whereas for a top connection air will be pulled in to the pipework.

 

[LittleSister]

With the fuel line coming from the bottom of the day tank then running out the top it still needs priming if you run it dry.

But with a day tank you could take the fuel line to the engine from the bottom the tank. The only argument put forward for taking it through the top of the tank is that if the tank fuel outlet to hose join fails, it avoids the whole of the content of the tank (1,000 litres in Fisherman's case, rather less for most of us) ending up in the bilge. With a day tank there will be only a relatively small spillage into the bilge, and plenty of fuel left in the main tank to get you home when you've sorted the problem.

I can see some merit in a day tank - including another barrier to crud or water getting to the engine, and easier to arrange a proper water/crud drain sump than in most main tank installations - but given its space and pumping complications, other options may be more attractive:
(a) 'modern' outlet taken through the top of the tank - just provide some means of easily manually priming after draining or leaks;
(b) 'old style' outlet taken from (near) bottom of tank - just make sure the joint is very reliable - double clipped, hose positively supported and protected from being pushed out of place.

 

[ghostlymoron]

I don't know how a top supply would have worked on my Mirror Offshore, their was no fuel lift pump so fuel was supplied to the engine by gravity only. Only about 6" head when the tank was low.

 

[Flica]

It does appear to be normal practice on more modern boats to have all the pipework at the top - in practice the input pipe being a few mm above the bottom of the tank only drags in the bottom nasties in a seaway.
When that happens (Dun Laoghaire 1994, les Sables d'Olonne 1998, Cediera 2001, Brindisi 2005) I know it's time to have the tank out and steam cleaned.
I've found a high-pressure inflation pump ideal for blowing the little bits of tar out of the lift pipe. I fear another tank extraction is currently due, after an incident last September off Kira Panagia.
I've never had anything fill my 4-stage filtration system, which seems to be such a feature of others' experience, so perhaps top-piping is quite a good idea.

The motor only does about 800 - 1400 hours a season, usually at 1800-2400r p m, so it's not terribly highly stressed and does return 1.1-1.9l/hr.

 

[fisherman]

A raised inlet is like a credit card, you pay in the end, unless there is a way of draining the muck as well. In 1988 we made a filter for fuel drawn from the tank base. It was basically a S/S house, about 300mm long and 200mm high, with a first floor and two chimneys. The fuel came in ground floor one end, went to the other end, up through two corners cut off the first floor, back to the first end, high up and so to the engine. Chimneys were bleeders. It was at a slight angle and the drain at the low end never showed any muck. After about sixteen years it was removed in a refit, and found to be jammed full with crud. This is the problem, the stuff becomes immobile, and that is why my primary sedimenter is on flexible pipes and not fixed to anything, I drain it a bit and then sloosh the muck round to mobilise it.

 

[NormanS]

It does appear to be normal practice on more modern boats to have all the pipework at the top - in practice the input pipe being a few mm above the bottom of the tank only drags in the bottom nasties in a seaway.
When that happens (Dun Laoghaire 1994, les Sables d'Olonne 1998, Cediera 2001, Brindisi 2005) I know it's time to have the tank out and steam cleaned.
I've found a high-pressure inflation pump ideal for blowing the little bits of tar out of the lift pipe. I fear another tank extraction is currently due, after an incident last September off Kira Panagia.
I've never had anything fill my 4-stage filtration system, which seems to be such a feature of others' experience, so perhaps top-piping is quite a good idea.

The motor only does about 800 - 1400 hours a season, usually at 1800-2400r p m, so it's not terribly highly stressed and does return 1.1-1.9l/hr.

I think if it had happened to me on four separate occasions, I would be doing something to stop it happening. Says he smugly with a dirt sump with drain, and a (near) bottom outlet to the various water trap/filters/engine.

 

[Flica]

I think if it had happened to me on four separate occasions, I would be doing something to stop it happening. Says he smugly with a dirt sump with drain, and a (near) bottom outlet to the various water trap/filters/engine.

I do - I take the tank out and clean it!"!

If you can think of a system to avoid it I suggest you patent it - usually such attempts are so failure prone that it's better to "bite the bullet".
You can reduce its occurence by never using a waterside filling station - or red diesel. Note that I've had no recurrence in 12 years - and my boat probably motors in one season as much as yours does in 5 years

 

[lw395]

Many yachts seem to have the pick-up a long way off the bottom of the tank, which means it takes a lot of water/heavy crud to stop the engine, but after a season or three there can be a lot in there, waiting to overcome the filter in rough conditions.
One boat I had, the pickup was so high, the engine would draw air if motorsailing in chop with less than half a tank.

 

[fisherman]

You can reduce its occurence by never using a waterside filling station - or red diesel. Note that I've had no recurrence in 12 years - and my boat probably motors in one season as much as yours does in 5 years

I get through several thousand litres of red pa: apart from using fuel set no real trouble taken. I will also leave a half tank from october to march and expect no problems. It may be down to having a dinosaur of an engine, Ford dover.

 

[NormanS]

I do - I take the tank out and clean it!"!

If you can think of a system to avoid it I suggest you patent it - usually such attempts are so failure prone that it's better to "bite the bullet".
You can reduce its occurence by never using a waterside filling station - or red diesel. Note that I've had no recurrence in 12 years - and my boat probably motors in one season as much as yours does in 5 years

If the fuel that you are in the habit of buying is so bad that you have to take your tank(s) out every three years to clean it(them), it would be well worth your while to install a day tank with an adequate dirt/water trap. You are however, correct in your assumption, as I have a sailing boat.

 

[Flica]

If the fuel that you are in the habit of buying is so bad that you have to take your tank(s) out every three years to clean it(them), it would be well worth your while to install a day tank with an adequate dirt/water trap. You are however, correct in your assumption, as I have a sailing boat.

You seem not to have grasped the fact that it's not dirt/water blocking the system in my boat, but little pellets of "tar" which are the product of bacterial action on the water-diesel interface. Having sailed about 26,000 nm on this particular boat I have a sound knowledge of the boat - probably greater than yours.
Mine too is a sailboat - but it does far more sailing than most - and even some motoring - I believe you are unaware of the full facts of the case - once emptied it takes about 20' to remove my diesel tank completely and about 15' to replace it - rather than revert to the 19th century practice of day-tanks (which still have to be emptied, and probably take all of 25' to do).
I now buy all my fuel from road stations - that is far cleaner than that supplied by waterside pumps and has a far faster turnover, avoiding the polymerisation prevalent with the increasing proportion of vegetable oils from the introduction of 2009/EC/1.
In France it is now <8% and the rest of the EC <7%.
So shall we agree to disagree on any benefit in your proposed "solution".

 

[NormanS]

You seem not to have grasped the fact that it's not dirt/water blocking the system in my boat, but little pellets of "tar" which are the product of bacterial action on the water-diesel interface. Having sailed about 26,000 nm on this particular boat I have a sound knowledge of the boat - probably greater than yours.
Mine too is a sailboat - but it does far more sailing than most - and even some motoring - I believe you are unaware of the full facts of the case - once emptied it takes about 20' to remove my diesel tank completely and about 15' to replace it - rather than revert to the 19th century practice of day-tanks (which still have to be emptied, and probably take all of 25' to do).
I now buy all my fuel from road stations - that is far cleaner than that supplied by waterside pumps and has a far faster turnover, avoiding the polymerisation prevalent with the increasing proportion of vegetable oils from the introduction of 2009/EC/1.
In France it is now <8% and the rest of the EC <7%.
So shall we agree to disagree on any benefit in your proposed "solution".

I have no desire to feed your personal animosity on this subject. If you are happy to have the risk of sudden engine failure, so be it. But sufficient to say that my tanks have NO fuel/water interface, because they have dirt/water sumps. The fuel that I use is good old fashioned high sulfur red diesel, with no vegetable/ bio content. It comes from a supplier who supplies several large car ferries, so has a very large turnover. I have no problems with my fuel - ever. I am not going to enter a childish willy waving contest re how much you motor with your sailing boat.