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Old 04-24-2017, 07:53 AM   #1
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Single Engine Fuel System Operation

New to us GB 42 Hull 803, Single Lehman Diesel.

Wondering what the recommended or pros/cons of operation off of ONE fuel tank at a time.

Based on my research there is a shutoff for both tanks, but only one return to STBD tank from the engine. Seems the STBD tank would fill up if you are only using the PORT tank for fuel.

Attached is a fuel system diagram.
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Old 04-24-2017, 07:57 AM   #2
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Your assumption would appear to be correct unless there is an equalization line between the two tanks.
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Old 04-24-2017, 08:07 AM   #3
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Greetings,
Mr. kr. I see no disadvantage to running with both fuel valves open. Doing so should allow tank equalization thus maintaining trim. Your thought of the STBD filling up if running on PORT is correct. I believe although Lehman's are reputed to return very little fuel to a tank IF you start with both tanks full you run the risk of an overflow on the STBD tank.
The only problem I can foresee is if you fill one tank with contaminated fuel, you may cross contaminate the other.
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Old 04-24-2017, 09:47 AM   #4
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Or you could have a valved return line to both tanks and return fuel to the same tank you are drawing from. We have 4 tanks so this option is pretty important. But, it seems to have worked well for a few decades on your vessel as is
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Old 04-24-2017, 10:11 AM   #5
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Non standard plumbing. Are you sure about the routing? All would be well if there is a low mounted cross tie line, check for that.
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Old 04-24-2017, 10:53 AM   #6
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My previous boat had a similar tank layout, and we could never leave both fuel valves open as even if the boat had only a slight list, the fuel would flow by gravity from the higher tank to the lower and increase the list.
Also, you should have the capability of returning fuel to the same tank that you are drawing from for both the main engine and the generator.
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Old 04-24-2017, 11:14 AM   #7
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Install one of these, problem solved . . . . . all of them.

The FV-65038 has 3 positions, left, right and off.

The FV-65038-A has 4 positions, left, both, right and off.

With either configuration, the the supply and return are switched together. One valve, one handle. It couldn't be simpler.




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Old 04-24-2017, 11:26 AM   #8
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@Rossland: You are very correct. Leaving an open crossfeed is a big nono, and has been pointed out as a contributing factor in several fatal accidents. Recreational craft designers tend to assume that the user won't understand this, so sufficient margins are built into the boat to prevent it from having serious consequences, but it's still a bad practice.
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Old 04-24-2017, 11:32 AM   #9
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Greetings,
I was not aware of the potential problems. I stand corrected and thank you.
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Old 04-24-2017, 12:07 PM   #10
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My fuel plumbing is the same as the OP diagram and I have a crossover line the is always open.
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Old 04-24-2017, 12:44 PM   #11
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Have fuel returns to all four tanks. I use one tank at a time.

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Old 04-24-2017, 12:50 PM   #12
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I have run single engine boats with two or more fuel tanks for years. Although not required I suggest you would be better off adding a valve that allowed you to return fuel from the same tank from which it was drawn.

I have always used a separate pump to drain one tank right before fueling so that I have one tank with old(good) fuel and one tank with the new fuel. If you must return the fuel only to the starboard tank you will contaminate both tanks if you take on bad fuel.

One approach with a single engine boat is to operate off the starboard tank one day and the port tank the next day. Thus equalizing out. This requires the ability to direct the fuel return.
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Old 04-24-2017, 01:22 PM   #13
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When I bought my NP43 the manufacturer recommended that the fuel crossover line be left closed due to the potential for a progressive list. Actually not an issue on my boat as I have a fuel transfer pump and the impeller keeps the fuel from passing through.

For a boat with a single fuel return all the OP needs to do is run first on the starboard tank and then the port tank. The time on the port tank will be less than the starboard tank.
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Old 04-24-2017, 01:27 PM   #14
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On some engines that have a high return the selector vave that also sets the return is the way to go.

No fuel filling unknown tanks overcapacity , and its much easier to handle the fuel heat that goes with the returned fuel.

Labeled valves are fine , but a drawing with the tanks valves etc is even easier to understand.

In the future YOU may not be moving those valves.
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Old 04-24-2017, 07:20 PM   #15
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My boat is now setup where the engine and generator draw and return to the starboard tank. I fill only the port tank. Then I transfer fuel as needed with a pump through a Racor 1000 that is a satisfactory fuel polisher. This allows me to watch new fuel going through the bowl to check for water and other contaminants. The plumbing is also setup to be able to polish the Starboard tank. The process also helps to use the older fuel first.

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Old 04-24-2017, 09:22 PM   #16
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Just curious...how often does one get "bad fuel" when boating in North America?
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Old 04-24-2017, 11:56 PM   #17
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He's not boating in North America. His boat's 'down south".
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Old 04-25-2017, 12:38 AM   #18
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Quote:
Originally Posted by FlyWright View Post
He's not boating in North America. His boat's 'down south".
South America? Australia?

I see lots of elaborate fuel containment/delivery/filtering/polishing systems and it makes me wonder...is it really that common to get bad fuel, and how often has it stopped anybodies engine?
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Old 04-25-2017, 01:30 AM   #19
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Had my boat's builder install a polishing system despite his contrary recommendation. My boatyard also disdained the need. As a result of miscommunication, the boatyard bypassed the polishing system. Nevertheless, the remnant system is still useful for transferring fuel among several fuel tanks, and haven't yet experienced a need here for polishing. Do have on-engine filters and dual Rycors.
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Old 04-25-2017, 08:13 AM   #20
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Quote:
Originally Posted by MurrayM View Post
South America? Australia?

I see lots of elaborate fuel containment/delivery/filtering/polishing systems and it makes me wonder...is it really that common to get bad fuel, and how often has it stopped anybodies engine?
I got a bad load of diesel in Mystic, CT (my home port) once. That was in the early 90s. It was bad enough to shut me down 2 times before I got it cleared out.
I found out months later that someone else in my marina also fueled up that same day and had the same issues. The "crud" looked like large coffee grounds. They were actually large enough to get stuck in the fittings of my copper fuel lines.
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