Bad fuel tank installation design - solutions?

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Plevier

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My boat has a standard Vetus fuel tank which is 800mm long x 400mm wide x 330mm high, capacity 88L like this http://www.vetus-shop.com/vetus-fuel-tank-diesel-88-litre-p-1794.html
The pickup is 200mm from one end. It's a vertical dip tube going down to 1cm above the flat bottom.
Unfortunately the tank is fitted lengthways across the beam - a serious design error in my view.
The result is that even with 20L of fuel in, a heel angle of 20 degrees will cause it to suck air and stop the engine. It's happened and caused an anxious few minutes.
So the effective fuel capacity is reduced to about 60L.
It's simply not practical to remount the tank lengthways as it should have been designed to start with. I can think of 2 makeshift remedies which could reduce the problem somewhat:
1 Make a diptube with a bend or crank in it so it picks up halfway along the tank.
2 Use an overlength very flexible dip tube with a weighted end so it can follow the fuel around the tank bottom. This approach is common on model aircraft and hand held equipment like chain saws and seems to work well on this small scale, and I think is also used on some full sized aerobatic aircraft. Anyone tried it on a boat?

Any comments and other ideas appreciated.
 
The flop tube idea sounds good, but may be difficult to implement successfully on a boat's diesel tank. Initially you need to work out the geometry to avoid baffles or any fittings it could get hung up on, but unfortunately our tanks are famous for accumulating crud and this would be stirred up by the tube swinging around on the bottom - you wouldn't be able to arrange the pick up to be above the bottom unless you still accept a percentage of unobtainable fuel with the tube never reaching the bottom.

It's likely that the best results would come from putting in a new dip tube at the centre of the tank.

Rob.
 
Well if nothing esle you have answered the riddle of why my hedge clipper has been playing up since I replaced the fuel tube.
 
Rob you are right the baffle would defeat the flop tube. It's moulded in and is like a tube from top to bottom with just a bit of space each side. See the dwg in the link above.
I can't put a new dip tube in at centre but could make a cranked one to reach there. I'll have to do some more trig and calculate the improvement.
Thanks.
 
birdseye said:
Well if nothing esle you have answered the riddle of why my hedge clipper has been playing up since I replaced the fuel tube.
Click to expand...

Your mower shop will have special very flexible tube probably silicone. The end weight is normally a gauze or sintered filter and they block easily. Wasted hours sussing out that on a strimmer!
 
Thanks for correction, yes Tygon F4040A is the stuff. Clear yellow. The data sheet doesn't say what it's made of. It's not cheap but it's b good, doesn't harden.
 
My tank is tall, 600 x 450 in horizontal area, but 1500 deep. I have to steam-clean it every 10-12 years.
I can't see a viable solution to your problem short of a new, remounted tank. A possible solution is a "floating" pick-up, OK except in short, sharp seas when it tends to pick up more air than fuel.
There is really, IMHO, no solution but replacing the tank with on which is deep and small X-section area.
 
Have you enough room to fit a 1 litre tank below the level of the existing tank? You position this small tank so it is fed with two pick up pipes, one from either end of your existing tank. you have a new pick up pipe from the 1 litre tank an inch from the bottom. Your one litre tank needs to be something like a fire extinguisher shape installed standing up. This set up will ensure that the small tank always has fuel flow to it from either end of the main tank.
We used to do this set up to ensure fuel injection pumps got a good supply of petrol when racing cars offroad 15 years ago.
 
Plevier said:
Thanks for correction, yes Tygon F4040A is the stuff. Clear yellow. The data sheet doesn't say what it's made of. It's not cheap but it's b good, doesn't harden.
Click to expand...

A new tank for my Ryobi strimmer, complete with tubes and pickup was only around £9. The original (black) tubes in the tank had broken up into little pieces, the replacement tank had this clear yellow tubing
 
geem said:
Have you enough room to fit a 1 litre tank below the level of the existing tank? You position this small tank so it is fed with two pick up pipes, one from either end of your existing tank. you have a new pick up pipe from the 1 litre tank an inch from the bottom. Your one litre tank needs to be something like a fire extinguisher shape installed standing up. This set up will ensure that the small tank always has fuel flow to it from either end of the main tank.
We used to do this set up to ensure fuel injection pumps got a good supply of petrol when racing cars offroad 15 years ago.
Click to expand...

Nice idea, unfortunately no, little room below it.
 
charles_reed said:
Outside the square - why not replace both, side by side?
Unless the boat is used on inland waterways, the black water tank is, surely, unnecessary.
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Possible at high cost and loads of plumbing work, yes.
Having just returned from a trip with several nights anchored in little bays and in the Morbihan, yes I think it's necessary. Compulsory in some countries aren't they?
 
geem said:
Have you enough room to fit a 1 litre tank below the level of the existing tank? You position this small tank so it is fed with two pick up pipes, one from either end of your existing tank. you have a new pick up pipe from the 1 litre tank an inch from the bottom. Your one litre tank needs to be something like a fire extinguisher shape installed standing up. This set up will ensure that the small tank always has fuel flow to it from either end of the main tank.
We used to do this set up to ensure fuel injection pumps got a good supply of petrol when racing cars offroad 15 years ago.
Click to expand...

That's something like a solution.

I have two fuel tanks, one either side, connecting by a low-going hose/pipe and the fuel is taken from the centre.
 
Some sort of swirl-pot or small 'day tank'?
I modified my first boat so that the fuel pick-up was in a small sump at the bottom of the tank.
The sump was a brass skin fitting blanked off. The tank sat on a shelf, with a gap under it at one end, so a hole in the shelf for the sump to go through did the job.
It did mean that any water (etc) went straight to the filter but I was happy with that.
Another thing that can help significantly is to add a bowl type filter with the bowl upwards, so it collects air. It then takes a lot more air in the pipe to stop the motor.
 
If Vetus calls them baffles I would not like to see them design a 50000 ton tanker.

I fitted two stainless baffles shaped to the interior profile one each side of the centre support 45 degree angle and 2 clamping studs
Needed a lot of patience and an extractor fan for the foul air, all done with one hand,
 
I would install a second small tank - about a gallon, depending on engine size, close to the engine and from which the engine is fed.
An electric pump would circulate fuel (or air) from the main to this aux tank continuously, but there would be enough fuel in the aux tank to last the heeling duration.

A non return valve in the pump feed to the aux tank might be needed if its higher than the main tank.
 
Thanks for all the comments and ideas.
Charles is right, a narrow vertical tank would do it, but very difficult.
A small buffer tank would also do it but there is a problem of little room below the main tank and I am nervous of putting in a connection at the bottom. Difficult to seal with high integrity to a blown PE (or PP) tank. All current connections are on a top plate.
A pump to the buffer tank is extra complication, cost and something else to go wrong.
Lots of head scratching needed.
I'm really p'd off that an expensive, not bottom of the market, boat only 8 years old was done like this. I wonder if current production (now by Hanse) is the same?
 
If you cut off the top of the tank leaving a wide flange, you can then get in easily and make any modifications necessary. Then make a new top sealed into place and removable for future cleaning. Once inside you can alter the baffles to fit the "clunk" (the helicopter pick up arrangement already mentioned).
 
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