Twin tanks and fuel return

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Polly1

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Went sailing this weekend and ran out of fuel repeatedly even after topping up from the Jerry cans, that is how I learned the fuel senders were stuck on my new boat. I assumed there was a leak somewhere and the bilge pumps had pumped it overboard but I couldn't see where the fuel was going. Then I got to thinking maybe I had not paid attention to the shut off valves and I was drawing fuel from one tank and then the fuel return was emptying it into the other. I got back and a piece of rope dipped into the second tank showed it to be pretty full.
I have not had a twin tank set up before so it was all a bit new to me. Has anyone experienced anything similar?
 
At anchor in the morning we went over to the only other boat anchored at the island, a new 35ft yacht and asked to buy 5 litres of diesel from them. I had checked the tank I was using internaly and there was only about 2 litres left. Only one mile away was a marina but across some difficult water that I didnt want a stopped engine for. However they had "no fuel to spare" on the way to their home marina about 5 miles away and suggested we canoe across in the canoe that we had paddled over to them in with a jerry can. We were pretty stuck so we went again to ask them to re consider but got the same answer.
In the end we bought some from the ferry that came in and as we left the yacht owners waved cheerfully at us.
 
Yes , when the red/white fuel problem came up in Ostend I fitted another tank which was basically a plastic tank from a RIB to take red for use whilst pottering at home. I cleaned the main tank & filled with that with white. The idea being that when going foreign I would remove the spare tank( has a handle & quick release connection) & change the filters. then run on the main tank.
The bit of red in the pipes would not be a problem if I drained them & ran some white through & changed it a couple of times.
What i did not realise was that the return actually still went to the main tank & that the amount of fuel returning was really very large. So much so that it emptied the reserve very quickly & filled the white tank which then overflowed over the deck & b..gered up the whole silly idea. It mixed red with white & contaminated 30 litres of white
So I cleaned out the main tank again & binned the spare tank (& 30 litres of "pink"). Now I always run on white. But as 75% of my sailing is foreign I can refuel in France, Holland etc anyway
 
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My boat has twin tanks. When I select the tank that I am going to use, I also select which tank the return is to go to. Seems perfectly logical and simple.
 
We have two tanks with 50 gallons each, the return goes to one of them so we think of it as the 'master tank'. There is a manual connection pipe which could be used to 'balance' the tanks. Our fuel polisher can connect and pump to either tank and we use this to transfer fuel from the slave to the master tank. We find it simple and confidence boosting to know that the transferred fuel is clean.
 
I have 3 tanks.

I made up a 3 way valve that had 2 sections so when the valve was moved to direct fuel from a particular tank the return was also moved to the same tank.

I also setup a fuel transfer pump so I could transfer fuel from any tank to any other tank. This was arranged so the fuel passed through the primary filter so could also polish the fuel at the same time.
 
One boat I've sailed on a bit has a 5 gallon 'day tank' which the engine draws from and returns to.
It's filled from any of three big tanks.
Only time I've ever measured the returning fuel flow, on a 3GM30, it was a lot less than people seem to expect? More fuel being burned than returned?
 
Polly1 said:
At anchor in the morning we went over to the only other boat anchored at the island, a new 35ft yacht and asked to buy 5 litres of diesel from them. I had checked the tank I was using internaly and there was only about 2 litres left. Only one mile away was a marina but across some difficult water that I didnt want a stopped engine for. However they had "no fuel to spare" on the way to their home marina about 5 miles away and suggested we canoe across in the canoe that we had paddled over to them in with a jerry can. We were pretty stuck so we went again to ask them to re consider but got the same answer.
In the end we bought some from the ferry that came in and as we left the yacht owners waved cheerfully at us.
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it’s not easy to siphon diesel from my tank, what about your tanks?
 
I carry spare fuel in jerry cans but i also carry a single 5 litre super emergency can. My theory is that once all the spare fuel is used up & I run out of fuel I never put the final 5 litres in. I will then actually sail (yeah, I know I am a dreamer!!! but possibly dooable) to a port; once there, put the 5 litres in the tank, then I know that I have enough to get in.
 
I discovered that my return was to only one tank when I first boat my boat. It has. 650L main tank and another 250L. I turned on both taps so fuel was coming from both tanks. I was told the boat didn't have much fuel in the tanks and after running the engine for just a short while, fuel began spilling out from the breather pipe!

Basically the return goes to only one tank and the seller of the boat sold it full to the brim of nearly 1 tonne of fuel! Turns out the delivery skipper filled it up in the med and sailed it all the way back only using the engine to enter Falmouth.

A nice cherrry on the cake when buying the boat.
 
northcave said:
I discovered that my return was to only one tank when I first boat my boat. It has. 650L main tank and another 250L. I turned on both taps so fuel was coming from both tanks. I was told the boat didn't have much fuel in the tanks and after running the engine for just a short while, fuel began spilling out from the breather pipe!

Basically the return goes to only one tank and the seller of the boat sold it full to the brim of nearly 1 tonne of fuel! Turns out the delivery skipper filled it up in the med and sailed it all the way back only using the engine to enter Falmouth.

A nice cherrry on the cake when buying the boat.
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I'm assuming (dangerous I know) that your two tanks are at roughly the same level. If you chose to run with both fuel cocks open, which would allow the tanks to cross level, if the boat was on an even keel, how would fuel come out of a breather? Something doesn't add up here.
 
NormanS said:
I'm assuming (dangerous I know) that your two tanks are at roughly the same level. If you chose to run with both fuel cocks open, which would allow the tanks to cross level, if the boat was on an even keel, how would fuel come out of a breather? Something doesn't add up here.
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Each tank goes via a racor filter first which is assume would stop one levelling into the other. So as the fuel returns to the main tank it just keeps adding until it overflows. That's my thinking anyhow.
 
OP has to my mind 2 choices. Either connect the 2 tanks so that they are effectively on by cross connection so they are constantly self leveling or Modify the system so that selection of one tank will also select fuel return to that tank. This would be done by mechanically coupling 2 selector valves perhaps by a connecting bar to ensure that the 2 valves operate in unison. I think generally despite what has been said return fuel is a lot more than what is used perhaps depending on throttle setting. ol'will
 
William_H said:
OP has to my mind 2 choices. Either connect the 2 tanks so that they are effectively on by cross connection so they are constantly self leveling or Modify the system so that selection of one tank will also select fuel return to that tank. This would be done by mechanically coupling 2 selector valves perhaps by a connecting bar to ensure that the 2 valves operate in unison. I think generally despite what has been said return fuel is a lot more than what is used perhaps depending on throttle setting. ol'will
Click to expand...

Permanent cross levelling on a sailing boat could lead to some interesting outcomes. :rolleyes:

Surely it's not too complicated to choose to which tank the return goes, without introducing mechanical linkages etc.
 
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