Help with trawler fuel manifold design

[albinalaska]

Good day to you!

I'm looking for advice with regards to updating the fuel system on our vessel. I've attached a quick draw.io diagram showing the current system. It is simple and has seemed to work for the life of the vessel. However, as we continue to refit the vessel and replace all of the hoses and fittings and service the tanks, I was looking to improve the system while we're at it.

ISSUES WITH CURRENT SYSTEM:
1. The tanks don't talk to each other. On our trip up from Seattle we found a gate valve closed on the starboard main tank which caused a list we had to mitigate throughout the voyage by manually pumping fuel from the starboard tank deck fill and dumping it into the port tank deck fill. This was a "new to us" delivery so opening the gate wasn't an option as we didn't know why it had been closed and didn't want to dump a couple hundred gallons of fuel in the engine room out in the middle of nowhere. If we can transfer fuel internally through a manifold that would be much easier should any issue arise in the future.

2. Uneven distribution of fuel. There was a generator (that has been removed) that drew from a "T fitting" on just the port main tank. I don't like the idea of tapping into main lines on an isolated system because of the unbalanced draws of fuel which would only continue to affect our ballast moving forward. Further, we are upgrading to a Hurricane ITR heater that will need a good supply line of fuel. Even further, we have a Marco UP6 fuel pump that can move 600GPH and would like to be able to use a manifold to distribute fuel as desired to either tanks to pass through the filters to "polish" the fuel if ever necessary.

Current Design:
The smaller tanks rest in the bilge about 1-2ft lower than the mains which are outboard of the engines along the hull in the engine room. In my opinion, the centerline day tanks being lower than the outboard main tanks is of good design (for the time; 47 years ago) because it allows sediments to flow from the larger tanks down to the lowest point in the system. In theory the debris moves with the fuel and subsequently keeps the main tanks clear of debris that might otherwise accumulate. The smaller tanks could be removed and cleaned more regularly than the larger ones. However, I've read that some people use their day tanks differently; allowing only filtered fuel to go into them that they know is good. So another reason a manifold may be a good option.

New Design:
I'm struggling to visualize how to implement addressing the issues of the current system. I don't know if the four tanks should be independent of each other, connected as they currently are, or something else I have yet to consider. I'm also unclear how many manifolds I would need to have control over filling the tanks and routing their respective return lines. I've even seen designs where the manifold that feeds the engine also has the engine return hose going right back into the same manifold, which makes no sense to me. Also, if two returns are connected to one manifold, how does that ensure the distribution of fuel to two separate tanks is remotely equal? The questions could continue.

Any input is appreciated, again I've attached a drawing of the current system as well as a blank if anyone is feeling especially motivated to concoct a diagram implementing a manifold or manifolds and transfer pump or any variation thereof.

Really grateful for any assistance.

Kyle

 

[Mac2]

Your pictures didn’t load on my phone. To clarify: you have port and starboard main tanks that free flow down to two daytanks (centerline?). All my tanks have a single fuel line (two way) that goes to the below manifold. Both engines and both generators and my hydronic heater are tapped into the day tank. A reverso fuel pump transfers fuel through a Separ fuel filter to the desired tank. The PO ended up expanding the day tank by adding a free flowing fuel hose from the day tank (maybe 100 gallons) to the stern tank (around 1000 gallons).

 

[albinalaska]

Yes, that is correct, the two main tanks free flow down into the day tanks that are centered in the vessel. I just used centerline so far as to say "centered" to differentiate them from the outboard tanks on the diagram.

I've seen the reverso pumps, and it seems like they are a good option, but I guess I've got some knowledge gaps as I wasn't aware that single fuel lines could be two-way. So your hoses have fuel that flows both ways so you can fill the tanks as you see fit? How do your tanks vent with a single line? Have you had issues with air in the lines? Thanks much!

 

[Diep]

I have a couple questions to try and understand the situation:

If a valve on the main tank was closed, how did you develop a significant list? You would have ran out of fuel after moving 15 out of the Aux tank. At that point 15 gal would have moved from port main to port aux and maybe half of that amount would have returned from stbd aux to stbd main. So maybe 20 something gallons net shift. Am I missing something in how the system currently functions?

The small AUX tanks are lower than the mains. This means in the typical condition the main tanks will keep these tanks pressed up into the vent line, to the level of the fuel in the main tanks. Is that the case? I don't love the idea of that and would think it might be better to maintain the tanks separately so the aux isn't always overfilled.

If you separated the tanks, would 2x15 gal work for you as day tanks? Or would the replenish interval be a nuisance?

 

[albinalaska]

In reviewing the original diagram (that I drew on only from memory in the original draw.io diagram shown above) I've realized I've overlooked a few fittings. Attached is a drawing from our logbook that I made at the time we found the issue.

As I review it now, I see that both day tanks were summed together in the back of the engine room with some T fittings. So, in this case both engines drew from the "FWD AUX" tank, thereby dominantly using the port MAIN TANK. Some fuel undoubtably returned to the stbd main tank but long term, created a list. The list was small but noticeable at anchor after running 12–13 hour days.

Diep, you are correct, the auxiliary tanks would be full of fuel to the level of the main tanks and would even have fuel sitting in the vent lines at the same height.

I haven't considered the fill intervals - if we run through 3 gallons and hour underway that wouldn't allow us to go more than a few hours without running the transfer pump.

 

[Mac2]

Yes, that is correct, the two main tanks free flow down into the day tanks that are centered in the vessel. I just used centerline so far as to say "centered" to differentiate them from the outboard tanks on the diagram.

I've seen the reverso pumps, and it seems like they are a good option, but I guess I've got some knowledge gaps as I wasn't aware that single fuel lines could be two-way. So your hoses have fuel that flows both ways so you can fill the tanks as you see fit? How do your tanks vent with a single line? Have you had issues with air in the lines? Thanks much!

If you look at the blue fuel line that connects to the center of the manifold, you use the ball valve above or below the connection to push or pull the fuel. All engine return fuel goes back to the day tank. All other tanks are shut off. All tanks have a vent, so air is going out the vent when fuel is being pumped in from the bottom of the tank (via blue manifold fuel line) and air is being sucked in through the vent when the opposite is happening. I typically use my fuel polisher (with timer) to move fuel around. I’ve never had air in my fuel lines.

 

[Diep]

I am assuming the aft tank line #2 runs under the gen and ties in to the aft line.

In this case, it looks like you could close the fwd AUX #2 valve and cause both mains to draw from the STBD system as needed to re-balance the tanks.

If you teed in and added a line and valve between the two MAIN/AUX feeds you could open it to let gravity balance the tanks without running the mains or leave it open typically and they would stay balanced. I think most the Grand Banks have a line connecting the tanks like this.

This doesn't address your manifold questions/goals but maybe helps in the mean time. I think deciding if you want to create a 4 independent tank system or stick with a pseudo 2 tank system would help focus the creative efforts.

 

[albinalaska]

Diep, you are correct. That line does run under the generator as you described. Thank you for the information regarding just hosing the lines so the tanks can balance. I think I'd been operating with the assumption they didn't communicate because I forgot about the original diagram and anything after didn't include the T connections in the aft of the engine room. That would be a good work around.

I could tap the heater into the T where the old generator used. The gate valves turned out to be fully functional, so they are now open and seem to be operating as expected. Perhaps this is the easiest/ least invasive adjustment for now.

 

[albinalaska]

thanks so much to everyone who reached out with their input and advice. I wanted to follow up with this in case anyone is ever interested in this information. The manifold that we'll find sufficient for our needs is shown below. It's a fairly basic and straightforward process as I've learned more about but it was quite confusing sourcing the parts at first. (I can include a detailed order list if anyone decides they're interested)

We're going to keep the main tanks feeding the smaller day tanks and then into the send manifold to power the items listed therein, then the returns will come from their labeled sources and return to the larger mains.

There will be a transfer pump and secondary filter to transfer if ballast is ever an issue again or we decide to polish the fuel. The transfer can also serve as an additional channel if we ever need to add more goodies.

The fuel lines are all 3/8", the vents are (per CFR 182.450) 5/8", the manifold inlets (x2) are 1" that are stepped down to 3/8" and the outputs (x4) are 1/2" that are also stepped down to 3/8". The fuel needs of the engines and the ITR Chinook heater will be able to manage their draw with these sizes.

Any questions or further insight are always welcome! Thanks a bunch!