Fuel Tank Configuration

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gavin400

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My fuel tank tank slopes from back to front and has a v shaped bottom, so naturally forms a low spot at the front

The fuel take off comes from this point right at the bottom of the tank so any water and/or debris must be sucked right into the fuel system

I presume it has been like that for the life of the boat and I have had no issues in my ownership, but just wondering as most new tanks have a take off slightly above the tank bottom

I suppose the current set up means that water can not sit at the bottom of the tank and rot it

Any thoughts?
 
It won't be good if you were to put lots of water into your tank, all that water will get into the fuel system and maybe over whelm the filters.
You could take precautions about that, maybe a fuel filter with a water sensor in, lots of cars have them?

It is good, in that you don't have a permanent layer of water in the bottom of your tank breeding diesel bug.

So, in your position, I would be careful never to dump lots of unknown fuel into the tank in one go, keep an eye on the water separator and consider fitting a water sensor somewhere before the engine filter.
Alternatively, fit a higher feed for the engine to draw from and use the existing for removing dirt and water.
How much fuel do you use?
How and where do you fill up?
 
Various opinions on this, I guess. Some say a bottom take off will get any water into the filter bowl where it can be seen and dealt with, but as you say most tank take offs are now above tank bottom. I've had both on different boats and on balance, if you can get good access to the tank bottom or even suck around with a Pela, I would prefer the higher take off .. you can clean the bottom of the tank as part of a maintenance schedule so water and sludge doesnt continue to accumulate. The only problem we had with the take off at the very bottom of the tank was when a piece of crud got sucked into the take off pipe ... less likely with a higher take off, but still possible.
 
Wing Mark said:
It won't be good if you were to put lots of water into your tank, all that water will get into the fuel system and maybe over whelm the filters.
You could take precautions about that, maybe a fuel filter with a water sensor in, lots of cars have them?

It is good, in that you don't have a permanent layer of water in the bottom of your tank breeding diesel bug.

So, in your position, I would be careful never to dump lots of unknown fuel into the tank in one go, keep an eye on the water separator and consider fitting a water sensor somewhere before the engine filter.
Alternatively, fit a higher feed for the engine to draw from and use the existing for removing dirt and water.
How much fuel do you use?
How and where do you fill up?
Click to expand...

The tank is 140 ltr, but I use very little (about 5ltr a trip) and top up with road diesel from the garage
Currently the tank is empty as I have removed it for cleaning, and will have to refill at the marina - so that is a lot of possibly unclean fuel
There is only 20mm space between tank and cockpit sole so dont think that will allow a take off to be fitted?
I could fit a replacement smaller tank however the current tank also provides support to the cockpit sole (there are timber bearers between tank top and underside of cockpit)
 
extra filter with water sensor seems like cheap way forwards?
Many years ago, i yacht I raced on had big problems due to about a gallon of water and slime collecting in the bottom of the tank and eventually getting stirred up in rough weather.
 
gavin400 said:
The tank is 140 ltr, but I use very little (about 5ltr a trip) and top up with road diesel from the garage
Currently the tank is empty as I have removed it for cleaning, and will have to refill at the marina - so that is a lot of possibly unclean fuel
There is only 20mm space between tank and cockpit sole so dont think that will allow a take off to be fitted?
I could fit a replacement smaller tank however the current tank also provides support to the cockpit sole (there are timber bearers between tank top and underside of cockpit)
Click to expand...
Your tank is in the same situation as mine.

No need to fill with 'dodgy' marina fuel at the beginning of next season, I wonder just how long the fuel will be sat in their tanks come next April, just fill with a few trips to the garage. I have 50 lts worth of jerry can that I use to fill the tank with and as reserve on long voyages. Some garages, notably Sainsbury's have a 30 ltr limit per transaction, but usually garages are happy for me to fill my 50 lts.
 
If the take off is at the bottom of the vee shape then it would be an ideal place for a scavenging point for clearing water. So I would fit another take off for the engine somewhat higher than the existing take off so giving you a "water trap" Providing you occasionally suck fuel out of the lowest point into a glass jar (so you can check for water) you should be doing your best to avoid water and bug in your fuel. Alternatively fit a tube to the bottom of the tank bringing it forward to a point where you can fit a valve as a water drain. Then perhaps shorten (raise) the pick up tube to be above any sediment or water collection.
Aircraft have a similar problem with water in the fuel. Exacerbated by huge changes of ambient temperature. The design standard for light aircraft calls for .5% of tank capacity as a water sump. The drain is checked daily for water. Likewise fuel storage tanks are checked daily for water from the lowest point. But they use a floating take off so not until tank is empty is fuel taken from the bottom. I say do every thing you can to keep your filters/water traps clean. They should be a last line of defense. ol'will
 
Sandy said:
Your tank is in the same situation as mine.

No need to fill with 'dodgy' marina fuel at the beginning of next season, I wonder just how long the fuel will be sat in their tanks come next April, just fill with a few trips to the garage. I have 50 lts worth of jerry can that I use to fill the tank with and as reserve on long voyages. Some garages, notably Sainsbury's have a 30 ltr limit per transaction, but usually garages are happy for me to fill my 50 lts.
Click to expand...
There's no upside in buying lots of diesel which you're not going to use soon. It's not French wine, it doesn't improve with age!
Enough reserve to be sure of getting home is enough IMHO.


If I fill my car at a 'Pay at the Pump' place, it wouldn't take many jerry cans to hit he £99 limit.

BTW, it's worth checking the bottom of your jerry cans for water and crud, I think my previous owner had been syphoning fuel out of the cans, leaving ever increasing water and crud in the can.
 
gavin400 said:
My fuel tank tank slopes from back to front and has a v shaped bottom, so naturally forms a low spot at the front

The fuel take off comes from this point right at the bottom of the tank so any water and/or debris must be sucked right into the fuel system

I presume it has been like that for the life of the boat and I have had no issues in my ownership, but just wondering as most new tanks have a take off slightly above the tank bottom

I suppose the current set up means that water can not sit at the bottom of the tank and rot it

Any thoughts?
Click to expand...

You are correct that the accepted best practice is to take the fuel not at the bottom of the tank, but slightly higher. Inevitably, a boat fuel tank will get some water/dirt/debris in it at some point, so having a space where these can collect in the tank and be removed directly rather than getting into the filter is preferred.

With your installation, there are a few things you could do to engineer around the potential problem of contaminated fuel.
  1. Re-locate the tank point higher up, or install a stand-pipe (use the existing fitting for a drain as someone else suggested)
  2. Install a second filter in series
  3. Install a second filter in parallel with a diverter valve
  4. Do nothing, keep a few spare filters on board in case of a problem
The best option for you would depend on a number of factors, cost, hassle, etc. You state that you have had no issues, so option 4 maybe your choice. :cool:
 
I think I may install a take off so as not to draw fuel from the very bottom of the tank
And I can use the existing as a drain tap

I can see lots of dip tube assemblies on e-bay but they are all 3mm dia, I need a 7mm dia set up - does anyone know where I might find such a thing

Many thanks
 
Wing Mark said:
BTW, it's worth checking the bottom of your jerry cans for water and crud, I think my previous owner had been syphoning fuel out of the cans, leaving ever increasing water and crud in the can.
Click to expand...
Do you not check the jetty cans before you use them?
 
The take-off from my Sadler tank is in the flat bottom but the fitting protrudes upwards by about 2 - 3 cm. This keeps water out of the supply to the engine.

There is a brass drain plug right in the bottom but the tank would need to be almost empty before it is safe to use. Consequently I never used it and galvanic corrosion between plug and boss destroyed the fine plug threads. I was able to recut a bigger, coarser thread and fit another plug
 
Wing Mark said:
The can was full when I bought the boat.
White diesel with croutons.
Click to expand...
Goodness! I inspect the jerry cans on every fill up and use a Mr Funnel as I fill the tank; you will be amazed at how much crud that picks up. I am sure there is somebody sprinkling stuff over my shoulder as fill.
 
My car seems to do OK on a regime of changing the fuel filter every 100k miles whether it needs it or not.
I took the precaution of filtering the fuel from the can.

I now have to deal with the 5 litres I drew from the bottom of the tank with a Pela.
Tank wasn't too bad, for an old boat.
 
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