twin fuel tanks

[jneale]

I have two diesel tanks -
switchable 'port - stbd', 'stbd - engine', 'port to engine', 'both to engine', and 'off.'
I normally use the Stbd tank with the return going to the stbd tank.

I have an electric pump which I can transfer fuel from port to stbd when the latter runs low. In other words I am using the port tank as a dump tank

If I switch to using both tanks,
- would I have to return fuel to both tanks via a t connection at the injector runoff
- Which tank would run low first, or would I get sufficient draw from the port tank (through the switched off fuel pump) to get equal usage.

BTW - both fuel guages are pessimistic

 

[NormanS]

I would suggest that you are doing the right thing at present. Just think, in the event of having a serious fuel leak, broken pipe etc, you have a reserve tank.

My own boat has two tanks, but unusually for nowadays, the fuel outlets are from near the bottom of the tanks, from a cross-connection pipe between the tanks. This means that to supply the engine from both tanks at the same time, both tank valves would be open, thus cross levelling the tanks. I always supply the engine from one tank or the other, never both.

My tanks also have small drainable sumps, which is the ideal way to stop any build-up of water and dirt.

 

[FrancisRutter]

When I had a Coaster 33 with twin tanks, I always filled only one tank from any one source. I was glad of that policy when I picked up a load of dirty fuel in Paris.
My nephew, bringing the boat home [with the mast left in Lowestoft, so no useful sails] found that the engine stopped between the separation zones. He phoned me and all I needed to do was to tell him to switch the feed from the stbd tank to the port tank. He did, and got home to Lowstoft with no more trouble.
I was able to change the filter and polish the fuel at leisure in harbour.

 

[BlueLancer]

I would suggest that you are doing the right thing at present. Just think, in the event of having a serious fuel leak, broken pipe etc, you have a reserve tank.

My own boat has two tanks, but unusually for nowadays, the fuel outlets are from near the bottom of the tanks, from a cross-connection pipe between the tanks. This means that to supply the engine from both tanks at the same time, both tank valves would be open, thus cross levelling the tanks. I always supply the engine from one tank or the other, never both.

My tanks also have small drainable sumps, which is the ideal way to stop any build-up of water and dirt.

I have a similar set up, how do you get a fuel reading for your gauges.On mine the gauges are on the side of the tank near the bottom.They now do not work,and were inconvenient any way. I want to have gauges on my console.I do not know what to use as a fuel indicator in the tank its self.It would appear there is not room for a simple pivoting float as per a car.The old gauges did not have anything atached to them in the tank, and I have not found anything loose in the tanks itself so how did they work, Sorry for the thread drift.

 

[NormanS]

Bizarrely, my boat was built with a fuel guage for the starboard tank, and nothing for the port tank. The fuel guage is / was innacurate and unreliable.
I fitted short clear plastic flexible tubes to the drain valves on the dirt sumps at the bottom of each tank.

Having run off some fuel into a container, to get rid of any water or obvious dirt, which I do quite frequently, and always after being out in heavy weather, I just hold the plastic tubes up against graduated marks. These marks correspond to every 20 litres, giving me an accurate reading for each tank.

I grant you that it isn't as easy as conventional fuel guages, but it works for me.

 

[Deleted member 36384]

.... how do you get a fuel reading for your gauges ..... I want to have gauges on my console.....

If you search the Vetus Catalogue for example, you will find fuel level sensors that fit on the outside of the tank and transmit the level to an electronic gauge. No drilling or tapping into the tank.

If I switch to using both tanks .... would I have to return fuel to both tanks via a t connection at the injector runoff ...

I have two tanks and the drain returns to just one tank. I dont know why it does this.

If I switch to using both tanks ..... Which tank would run low first, or would I get sufficient draw from the port tank (through the switched off fuel pump) to get equal usage.

It is likely that one tank will be be drawn down easier than the other. How much of a difference is entirely dependant on the pressure loss of each pipe / hose system and the height difference in fuel between the tanks. This is a factor of length and restrictions caused by fittings. You may find that a tank that has a shorter hose / pipe run to the lift pump will preferentially draw down. Then again if the fuel lines are over size, relative for the pressure loss, there may be no noticeable difference.

There is another way. You have a day tank / header tank and pump tank fuel into that. The take off would be from the top of the day tank to your engine so that you do not suck up water or crud from your main tanks. This method is common on large installations and may be impractical on a smaller set up. Never the less, some long range cruising yachts (40' for example) have this arrangement.

 

[WoodyP]

I have a Kingfisher K30. (Sounds like AA). These come with two fuel tanks, one in each keel.
I have been more than happy on several occasions to have the ability to switch from one supply to the other when the fuel filter blocked up. Each tank should have the return to itself. You don't want to mix up one set of rubbish with the clean tank.

 

[boatmike]

You have answered your own question if you think about it. You should only ever use one tank at a time as there is a possibility (probability) that you will draw fuel from one tank and return to the other otherwise.Not a good Idea! It simply won't work. If you want to "tandum" tanks you need to have a main feed and return to one with the other replenishing it when low. there are various ways of doing this but frankly as the system you have works OK I would leave well alone. The "both" setting is probably simply there to allow switching from one to the other without getting airlocks or causing fuel starvation when switching over .

 

[rob2]

I think the belt and braces approach of having your twin tanks arranged as two complete duplicate systems makes sense, especially with a filter on each supply. With regard to guages, I would mention that a permanently fed sight glass is a fire risk as in the event of breakage or fire, the whole content of the tank can spill into the conflagration! It is important to have a valve to isolate the sight glass except when taking a reading.

A similar approach was taken by an acquaintance who took a feed from the bottom of the tank to a copper stand pipe arrangenment with a vertical sender in it and a breather from the top to allow it to self level. One of several sources of guages and senders is Tek Tanks, their website might give you some ideas.

Rob.