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Old 06-30-2020, 08:03 PM   #21
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Have four tanks and single engine, two tanks on each beam, using one tank at a time. Easy to balance using valves (choice among four to-engine and same number for return while running the engine) and sometimes use an in-system pump, rarely necessary.
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Old 06-30-2020, 08:34 PM   #22
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Cartouche,
My MS390 used to list a little to Port after a long cruise of more than 5 hrs however, the tanks will auto balance via the crossover line once I stop for the night. I have the same setup with a single Cat3116 with two RACOR–75500FGX2 Turbine Series Fuel Filter/Water Separator. I was able to resolve my listing issue by using the port tank only once It was 1/2 full. this way, the fuel pump will remove any blockage from the supply hose from the port tank. in my case it, there was some what clogged as I had some dark green stuff in the filter.
swapped the filter and have not had the listing issue anymore for a over a year so far.
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Old 06-30-2020, 09:27 PM   #23
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Originally Posted by jhall767 View Post
Not sure if you are doing this but that crossover line is required to be closed when underway.

Also I would advise against running from both tanks at the same time with both returns open. Any flow issues and you could actually transfer all the fuel to one tank creating a very unbalanced boat. And maybe even a fuel spill. You should probably alternate every couple of hours.

BTW extra beer is always good portable ballast.
Many thanks so to be clear I should shut off the Crossover line, and then select which tank to draw from right now I have the crossover open and both tanks drawing to the Racor
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Old 06-30-2020, 09:33 PM   #24
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Originally Posted by jhall767 View Post
Not sure if you are doing this but that crossover line is required to be closed when underway.

Also I would advise against running from both tanks at the same time with both returns open. Any flow issues and you could actually transfer all the fuel to one tank creating a very unbalanced boat. And maybe even a fuel spill. You should probably alternate every couple of hours.

BTW extra beer is always good portable ballast.
Not sure why but the mainship Manual tells me to not close the crossover line when engine is running, any ideas as to why? (Page 5.4)
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Old 06-30-2020, 10:04 PM   #25
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A guess but if there is only one return line to one tank then all the return fuel will stay in that tank and cause a loss of fuel. The balance line may be needed to at least try to effect a balance.

When closing the balance line the return line should also be directed to the same tank you are drawing from or you could actually overfill the tank that the return fuel goes to and dump fuel out of the vent line. Don't ask how I know.

I looked for any mention of two return lines, one to each tank, with valves so the return fuel can be directed. If the fuel is not able to be directed to the tank being drawn form then you need the balance line.

Maybe a project for another day to correct.

If you go this route, directable return lines then you must ensure that you NEVER shut of the active one before opening the other valve or injector pump damage can occur.
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Old 06-30-2020, 10:56 PM   #26
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Similar problem on my Willard 36 with single Perkins 4.236 75hp and twin saddle tanks of 225 gals each, though to a lessor degree than OP. For me, boat needs to be re-trimmed - no clogs or otherwise. Over the years, she got a bit heavy on port side, which caused more fuel to flow to port side, and trim gets worse until she has 3-4 degree of trim at rest. Not much but annoying. When she's done with her refit, I'll put 150 gals in each tank then use movable lead ballast to trim her to zero degrees trim. I consider this normal after 50 years and a major refit.

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Bingo!! my solution for everyday boating. two 50# ingots wth barn door handles screwed to the top for ease of handling.

This quote is confusing and contrary to operations as I am familar with. In all of my boats, a common fuel line is in play from both tanks. My return line is tee'd to both tanks. I have never has an issue and am confused as to why I would save a pluged line in the mix. What are the odds? and then of not being aware were it to develop. O well, on to reading more on the subject.
.

Not sure if you are doing this but that crossover line is required to be closed when underwayAlso I would advise against running from both tanks at the same time with both returns open. Any flow issues and you could actually transfer all the fuel to one tank creating a very unbalanced boat. And maybe even a fuel spill. You should probably alternate every couple of hours.


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Old 07-01-2020, 06:55 AM   #27
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A guess but if there is only one return line to one tank then all the return fuel will stay in that tank and cause a loss of fuel. The balance line may be needed to at least try to effect a balance.

When closing the balance line the return line should also be directed to the same tank you are drawing from or you could actually overfill the tank that the return fuel goes to and dump fuel out of the vent line. Don't ask how I know.

I looked for any mention of two return lines, one to each tank, with valves so the return fuel can be directed. If the fuel is not able to be directed to the tank being drawn form then you need the balance line.

Maybe a project for another day to correct.

If you go this route, directable return lines then you must ensure that you NEVER shut of the active one before opening the other valve or injector pump damage can occur.
The return goes to the starboard tank but even with the Cross over line closed the engine will still draw from both tanks
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Old 07-01-2020, 10:46 PM   #28
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The return goes to the starboard tank but even with the Cross over line closed the engine will still draw from both tanks
Yes the engine will draw from both tanks but with the crossover closed the return fuel will go to one tank only so that tank can be overfilled and overflow unless there are individual returns to each tank and both are operable or switched to the main draw tank. This can also lead to a list after a run.

Just be aware.
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Old 07-02-2020, 05:56 AM   #29
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The return goes to the starboard tank but even with the Cross over line closed the engine will still draw from both tanks

And this is why you need to keep the cross over line open.


I too would check your vent lines. A low spot in a vent line that gets flooded with fuel from an overfill will block the vent and cause all sorts of problems. It's easy to test by opening the fuel fills for both tanks, turning them into vents, and see if they balance out. I had this exact issue with interconnected water tanks on another boat
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Old 07-02-2020, 08:36 AM   #30
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And this is why you need to keep the cross over line open.


I too would check your vent lines. A low spot in a vent line that gets flooded with fuel from an overfill will block the vent and cause all sorts of problems. It's easy to test by opening the fuel fills for both tanks, turning them into vents, and see if they balance out. I had this exact issue with interconnected water tanks on another boat
Another reason to check is because it's the simplest to fix problem. I always try to start there when gremlins creep aboard our boat, because, well, it's the easiest and might save me a bunch of unneeded head scratching and labour.

Surprisingly often, it is the simplest fix that solves an issue.
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Old 07-02-2020, 10:29 AM   #31
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Balancing cross over line

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Originally Posted by twistedtree View Post
And this is why you need to keep the cross over line open....... It's easy to test by opening the fuel fills for both tanks, turning them into vents, and see if they balance out.
Good advice!
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Old 07-02-2020, 11:10 AM   #32
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The single return line is very interesting. The reason for keeping the crossover line closed is so that the tanks don't become unbalanced causing a list which then causes the tanks to become even more unbalanced.

It's rare but years ago we had a sunken boat at our marina after an extremely low tide where it laid over on it's side and all the fuel transferred to the port tank. When the tide came back in it flooded the boat and it never refloated because of the angle and the water flooded the side of the bilge and didn't even activate the float until it was too late.

Boat was a 40' ish aft cabin.
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Old 07-06-2020, 01:08 PM   #33
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Seeker has a list from having a generator removed and never re-trimmed. So if the crossover is opened, she lists more and more as fuel migrates to the low side tank from the highside tank. Never enough to cause a problem but noticeable.
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Old 07-06-2020, 01:50 PM   #34
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My tanks rarely “balance” as I switch to one tank and switch to the other when I notice a bit of list.
Since I re-configured my fuel valve Positions I now can reach all four while underway. So I can raise one engine compartment hatch cover (floor) and change to draw from the other tank in about two minutes.
I one can’t notice the list it dos’nt need to be messed with .. IMO.
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Old 07-06-2020, 02:10 PM   #35
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As a 390 owner, it was my understanding that the crossover was supposed to be left OPEN. In the 5 years I had mine - i never closed it. Do NOT close the valve if you have a single returning to one side! The crossover is there to equalize the returning fuel.

Yes - some 390’s had a SLIGHT list to port... usually if owners replaced starboard side furniture with something lightweight. I had a HEAVY sleeper sofa in mine, and my boat remained balanced. I never had a problem with fuel system or balance. I never tried to dip my fuel tanks. Dipping really only works as a comparator if both tanks and filler piping are identical. I am not sure if that is the case - but you could look and see. Other than that - if you can get a dipstick in - you could determine relative, but not precise quantity.

Open the fuel fillers one at a time and see if you have air going into the fuller tank (as it transfers to less filled side. Because the transfer line is small - it will not be a huge rush of air. Use a piece of paper or card stock to see if it gets sucked against the opening. If fuel moves when one or the other fuel filler cap is opened - you probably have a vent issue. You can test both sides to determine which vent is clogged.

If you still have high fuel on one side and open caps make no difference - close off both fuel transfer valves - remove hose and check for obstructions. Open each valve with a bucket under to check for flow.

Lastly if fuel is ok and you have the slight port side list - consider your water tank locations and fill status as others have mentioned. We only regularly used our primary tank which was located centerline behind the stairs going below. We had two aft tanks that could effect trim as you could pull from them one at a time. Not all 390’s had the same water tankage setup.

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Old 07-06-2020, 04:07 PM   #36
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From the description, the boat is equipped with top-feed (standpipe) fuel supply. This introduces another set of issues. What if the side with the most fuel has developed a pinhole in the standpipe or even farther along toward the Racor - not so much that engine performance suffers but maybe enough for a "fuel preference" to get established?

My single 6LPA Yanmar boat came from the factory with the fuel supply to the engine teed to a single Racor from the bottom-fed sluice (crossover) line and the return only to port AND the fuel gauge on the console reading only port. How dumb is all that mess?

If I had the OP's boat, I would decommission the standpipe feed and go to the system I now have with the bottom feed via the sluice line feeding to twin selectable Racors, selectable return to either tank, and a selector switch to read the level of either tank at the console. NOW you have complete control of the tank levels.

Do check the vents!
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Old 07-06-2020, 04:09 PM   #37
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If I do end up with a diesel trawler, it will be my first diesel powered boat with more than one fuel tank (previous were sailboats), so my first experience running with various valves and etc.

Reading through this thread I was able to gain a better understanding of how the system(s) work. OP: Sorry you have a problem, but your thread has been enlightening so thank you.

I now have a question that might also be of interest to the OP.

So let's say that like the OP, you have a single engine, two (saddle) tanks, a crossover, and only ONE return line (to only one side's tank). Presuming one does not mind doing the labor, is there any good reason not to add a return (with appropriate valves) to the other tank? Or to put it another way, what is the advantage to the user of the OP's "return to one side only so must leave crossover valve open" installation? Obviously fewer valves and fuel lines for the builder to install, but for the operator? Was it done as a "keep it simple and let's not confuse people with choices" type thing?

In summary, I want to test out my thought which is that while a system with return valves to both tanks requires more thought and action while operating; it also gives one more ability to control for list (which can be exacerbated by a waterfall effect as the low side tank encourages more and more fuel to head over that way through the "must be open" crossover). OTOH, the "only one return and must keep crossover open" is the "you don't need to think about it" approach (AS LONG AS the boat does not start to create a cascade of listing).

Thanks for any replies and OP, I hope this is useful to you as well (why I did not start another thread at least as of yet).

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Old 07-06-2020, 04:27 PM   #38
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Quote:
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If I do end up with a diesel trawler, it will be my first diesel powered boat with more than one fuel tank (previous were sailboats), so my first experience running with various valves and etc.

Reading through this thread I was able to gain a better understanding of how the system(s) work. OP: Sorry you have a problem, but your thread has been enlightening so thank you.

I now have a question that might also be of interest to the OP.

So let's say that like the OP, you have a single engine, two (saddle) tanks, a crossover, and only ONE return line (to only one side's tank). Presuming one does not mind doing the labor, is there any good reason not to add a return (with appropriate valves) to the other tank? Or to put it another way, what is the advantage to the user of the OP's "return to one side only so must leave crossover valve open" installation? Obviously fewer valves and fuel lines for the builder to install, but for the operator? Was it done as a "keep it simple and let's not confuse people with choices" type thing?

In summary, I want to test out my thought which is that while a system with return valves to both tanks requires more thought and action while operating; it also gives one more ability to control for list (which can be exacerbated by a waterfall effect as the low side tank encourages more and more fuel to head over that way through the "must be open" crossover). OTOH, the "only one return and must keep crossover open" is the "you don't need to think about it" approach (AS LONG AS the boat does not start to create a cascade of listing).

Thanks for any replies and OP, I hope this is useful to you as well (why I did not start another thread at least as of yet).

Frosty
Frosty, you seem to have it correctly thought out. Yes, it is dead simple to add a return to a second tank assuming like my boat, the tank connection was already there, just plugged. MS obviously made these simple and inflexible systems for the masses who just want to run the boat hoping everything works OK all the time. I prefer to have a hand in where fuel comes from and goes to.
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Old 07-06-2020, 05:35 PM   #39
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Thank you, Rich.

I knew this was something I was going to need to "get my head around" at some point, and the OP (and up-thread responses) provided just the head start I needed. I think I'd prefer the method where you need to think about it a little bit, but have more control. I'm sure I'd need to print out reminders for myself at first (such as always have a new destination for the return before shutting off the other one while engine running; this is a familiar concept from something like alternator output, but I didn't know it also applied to fuel pump).

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Old 07-06-2020, 07:58 PM   #40
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fuel tank balancing

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We have a Mainship 390 with 2 Tanks port and starboard. I noticed a considerable list to Port yesterday (Fuel gauge was showing just off full) yesterday we fuelled up for the first time this year, and the starboard tank took $225.00 of diesel and the Port tank only took $50.00 of Diesel. both valves are open on the Equalization line at the bottom of the tanks and both Valves are open to the Racor, . I know the generator draws from the Starboard tank but we have only run it at Launch for about 5 minuets - any thought's

I had the same issue with twin tanks, twin engines, and genny drawing from one tabk only. It seemed to start after I had a pre engine "fuel cleaning centre" installled and after the tanks were filled. As it turns out, and after all logical reasons were dismissed, the engines draw fuel by taking the path of least resistance. As the one tank drops the pressure from the fuller one should make it easier to draw from. I didn't appreciate the list and the potential for it to not start drawing from the fuller tank so I installed a shut off valve where there normally would be a free from through the crossover. So now all the fuel from the port tank goes through the.port fuel filter first and the starboard tank feeds both the stbd fuel filter and genny first. If the stbd empties sooner I can open the cross over valve. Good luck. Stay safe.
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