refilling the day tank - how do you do it?

[Obelikx]

A technical question: how do you manage refilling your day tank?

A few years ago after installing a new day tank and an ultrasonic gauge, I managed to overfill the tank and flood the bilge with some diesel fuel (a mess to clean up). The reason: while in the marina the electronic of the ultrasonic unit gives a relatively rapid reading, in a seaway with the movements of the fluid surface, it takes more than a minute before you get a reading of the actual level: and this led me to overfill the tank because my reading was still sth like half full …

A lesson learned the hard way. In a seaway, I now always use a timer and keep the finger on the fuel pump switch all the time during refilling.

After spending a few hours cleaning the diesel out of every corner of my engine room, I was convinced that I would quickly work on a solution … however, as usual with an old boat many other projects got priority.
Now, its again on the agenda for 2019. So I am interested how you guys manage filling the day tank? Manually? With an alarm? Fully automatic? And which sensors do you use? (As I like being in control of the actual fuel consumption and switch between main tanks to the day tank, I am more thinking of an alarm and/ or an relais that is switched of once a certain level is reached instead of a fully automatic system).

thanks a lot for your input

 

[angus99]

I guess my first question would be: do you need to fill the tank in order to get a day’s worth of fuel out of it?

I use the large (250-gallon) aft stoarage tank in our boat as a day tank. I need nothing close to that for a day’s run, but try not to allow the level to drop below 1/4. For this tank, I installed a new reed switch fuel level sender and a remote gauge in the engine room, where I can easily keep track of the amount of fuel being transferred as I go about my other morning ER checks.

 

[twistedtree]

By pump control was on a timer, and I had figured out the transfer rate, so could figure out how much time to dial in based on how much fuel I wanted to transfer. I got 30 gal for every 10 minutes on the pump. The tank also had a sight gauge which was a nice confirmation, but I only used it for that. Primary tank level was with Wema float sensors connected to a Maretron sensor and display system. So in daily operation I would monitor the maretron level, which by the way was alarmed if it got too low, see that there was room to transfer 100 gal, then go set the timer fro 30 minutes. I also had an alarm if the tank got too high.


It sounds like a lot of your problem is the ultrasonic level sensor. I don't know which one you are using, but I have had poor results from ultrasonic senders. By far the best results I've gotten have been from pressure transducers and the associated maretron devices. It's extremely accurate, responsive, and can be calibrated for any tank shape. If you can't install a sensor in the plumbing somewhere at or below the tank bottom, you can use their submersible sensor that gets lowered down into the tank, probably through the port now used by your ultrasonic device, with a sealed cover plate.

 

[Obelikx]

I guess my first question would be: do you need to fill the tank in order to get a day’s worth of fuel out of it?

I use the large (250-gallon) aft stoarage tank in our boat as a day tank. I need nothing close to that for a day’s run, but try not to allow the level to drop below 1/4. For this tank, I installed a new reed switch fuel level sender and a remote gauge in the engine room, where I can easily keep track of the amount of fuel being transferred as I go about my other morning ER checks.

Thanks a lot. Unfortunately, my 'day tank' is more a '6-8 h tank'; so I need to refuel more often and typically try to do it every 6 hours or so. While I do my ER checks every 2 h, I don't need to go below for the refuling as the pump switch is on my dashboard. So in the marina, my system works like yours, but in a seaway the fuel sensor is disturbed by the movements and than is too slow. Probably I should replace the tank to a larger one ...

 

[Obelikx]

By pump control was on a timer, and I had figured out the transfer rate, so could figure out how much time to dial in based on how much fuel I wanted to transfer. I got 30 gal for every 10 minutes on the pump. The tank also had a sight gauge which was a nice confirmation, but I only used it for that. Primary tank level was with Wema float sensors connected to a Maretron sensor and display system. So in daily operation I would monitor the maretron level, which by the way was alarmed if it got too low, see that there was room to transfer 100 gal, then go set the timer fro 30 minutes. I also had an alarm if the tank got too high.


It sounds like a lot of your problem is the ultrasonic level sensor. I don't know which one you are using, but I have had poor results from ultrasonic senders. By far the best results I've gotten have been from pressure transducers and the associated maretron devices. It's extremely accurate, responsive, and can be calibrated for any tank shape. If you can't install a sensor in the plumbing somewhere at or below the tank bottom, you can use their submersible sensor that gets lowered down into the tank, probably through the port now used by your ultrasonic device, with a sealed cover plate.

Thanks for your helpful comments. I was thinking of upgrading to Mareton for other systems as well. How does the pressure sensor react to bumpy sea conditions (cause this is when the algorithm of my US sensor takes his time (more than 1 min) before giving a precise readout. In the harbor or with flat seas its not a problem and it is very accurate and matches the sight glass reading.

 

[O C Diver]

I have never liked the idea of becoming dependent on a float or other type of level switch for turning a fuel transfer pump off. Think the timer is a far better way to go. Also prefer the "Tank Tender" system for monitoring liquid levels. One more area I don't need an electronic device to fail.

Ted

 

[saboga]

I have never liked the idea of becoming dependent on a float or other type of level switch for turning a fuel transfer pump off. Think the timer is a far better way to go. Also prefer the "Tank Tender" system for monitoring liquid levels. One more area I don't need an electronic device to fail.

Ted

But timers can fail too And you might have a brain-fart and set it to run too long. A timer and a float switch at the top of the tank seems like a reasonably redundant precaution.

Or get a mechanical float valve that will close the fuel inlet when the tank is full. Nothing electronic to fail.

 

[saboga]

Something like this, maybe: Fluid Valves | Float Operated Level Control Valves

 

[cafesport]

Sounds like your day tank is venting into the bilge, not sure why you did it that way but you might consider a higher vent or “t”ing the day tank vent into another existing tank’s vent. Then any overflow will fall back into a fuel tank instead of into your bilge. Where is this day tank located? If it’s lower than the main tank/tanks that’s a good thing because you could also use it as a gravity sump to drain any and all water. Another benefit of having a lowest point day tank is the hydrostatic pressure differential will keep it full until the supplying tank level falls to the approximate height of the upper level of the day tank. No pumps needed and everything automatically gets filtered without running a transfer pump. Our day tank is only 30 gallons so when our saddle tank levels drop to below 400 gallons we have to manually transfer fuel which equates to flipping a switch every hour for 10 to 13 minutes. Not a big deal it’s actually part of the watch stander’s routine, along with engine room checks and keeping the deck log.

 

[O C Diver]

But timers can fail too And you might have a brain-fart and set it to run too long. A timer and a float switch at the top of the tank seems like a reasonably redundant precaution.

Mechanical commercial grade timers can fail, but given the number of times it will be used, getting struck by lightning during a snowstorm is probably as likely. Add a float switch as a safety if you feel it's necessary.

Ted

 

[BIG CAT]

I'm not a fan of ultrasonic level sensors. I have seen several fail in land based stand-by gens that caused overflow's. if your going to keep the sensor i would put in a madison float switch to cut off the fuel pump when you reach 95% full.

 

[Lepke]

I use a timer but before the timer, when the boat was new to me, I spilled fuel twice because I forgot the switch. Tank has a sight tube going almost the full height. It can also be filled thru a deck fill. I have no fuel gauges, all my tanks are measured by a dip stick.

 

[Obelikx]

Thanks guys, many really good ideas and helpful suggestions.

The ‘day’-tank is located higher than the lowest points of the two main tanks (2500 L / 660 gal each on both sides of the engine room from the bottom to deck level). Actually, the previous owner used it as a separate tank to have cheaper fuels for the central heating in winter – which is no longer legal in the Netherlands where you have to use the high tax fuel also for heating of a boat. So like 8 years ago, I converted it to a day tank. The top of the day tank is also situated a few inches lower than the main tanks and also has its own deck fill. However, I will further investigate the idea of having the day tank's overflow drain into the main tank. Perhaps I can simply install an overflow loop that drains into the starboard tank – thanks for that one . Would result in a simple system where I simply can fill the day tank until full and it would make a more complex solution unnecessary – with less chances for failure or error. Also the idea of a mechanical flow valve, shutting down the fuel supply to or from the pump is an interesting one that I will look into – might be tricky with supply lines from different tanks and also some fuel polishing and cross over possibilities for balancing the boat and the spare fuel pump etc. – but will make some sketches to look into that as well.

As suggested, I am currently investigate a combination of an overflow switch that cuts the power to the pump – and of course I would always want to use in combination with a timer. (Regarding the timer, the technical issues and quality are probably not the weakest point, but human input is, i.e. crew or me of course). Another limitation of the timer are the changes in flow rate: height of the fluid in the main tanks and the large SEPAR ® filter which nominally has some 2000G-7000L/h but once it gets a little clogged the flow rate changes and I change it only every 6-12 month (unfortunately had some experience with dirty fuel; and there is a second filtration step with dual 10 mic filter before the engine of course).

 

[sunchaser]

A technical question: how do you manage refilling your day tank? A few years ago after installing a new day tank and an ultrasonic gauge, I managed to overfill the tank and flood the bilge with some diesel fuel t

Pretty simple if you have calibrated sight tubes - do you have one on the day tank? If so, measure the pumping rate. Then set your timer to add a known quantity of fuel, but not so much to cause over topping.

Do you have a visual of the day tank level while cruising, meaning good ER access?

Just curious, why not eliminate the filter which apparently throttles the transfer pump?

 

[Obelikx]

tx
what you describe is how I am doing it at the moment (yes, I have sight tubes and an engine room were I can stand and walk around); and the changes in flow are slowly over days as the hight of the fluid column in the main tanks gets lower and the filter more clogged ...
I am just try to work out a more fool (i.e. me)-proof situation

(PS to answer you last question: once you ever got a load of bad fuel and had to change the filters several times in 'unfriendly' sea conditions when all the stuff is stirred up, you want and love the pre-filter even if it reduces pump flow and makes the flow more unpredictable

 

[sunchaser]

OB
Maybe install a two filter valved setup with vacuum gauges that tell you when filters start clogging. Check out SBar marine's spin on filter setup.

What kind of fuel transfer pump are you using - positive displacement or centrifugal? Are you sucking through the filter or pushing?

 

[Obelikx]

OB
Maybe install a two filter valved setup with vacuum gauges that tell you when filters start clogging. Check out SBar marine's spin on filter setup.

What kind of fuel transfer pump are you using - positive displacement or centrifugal? Are you sucking through the filter or pushing?

thanks. Centrifugal pump with suction for filling the day tank. has a vacuum gauge but not really helpful with the high flow rates (always very high)
and a two filter valved setup with vacuum gauge between day tank and engine
quite happy with this part of the setup though. For both filtration steps, I use SEPAR filters (MPW Worldwide), a German brand with high quality water separation and filtration - works like Racor, perhaps a little more expensive.

 

[C lectric]

www.sbmar.com

is I think who Sunchaser is referring to.

 

[koliver]

I have a day tank for my diesel stove, so its demands are low and my 2 gal tank will last 2 days between fills. If yours is used for mains, or some other higher volume use, you may not successfully use my system, but here it is:
I have the fuel return line from my port engine fill the day tank. the line is on a T connection at the top of the tank, with the stem of the T vertically into the fill attachment of the day tank. Once full, excess returning fuel returns to the port main tank. When between running days, there is also a Walbro pump on the fuel line, drawing from the same main tank and T'd into the fill line before the top of the day tank. If full, excess fuel returns to whence it came.

 

[Bkay]

I have the fuel return line from my port engine fill the day tank. the line is on a T connection at the top of the tank, with the stem of the T vertically into the fill attachment of the day tank. Once full, excess returning fuel returns to the port main tank.

I always thought this would be a sensible solution for keeping a full fuel tank for a heater. But I never saw it in practice. Glad to know it works.

 

[sunchaser]

Shall we take a step back and drift a bit? A few questions:

• What common problems does a day tank address?
• How large should a day tank be in terms of hours before hands on re-fill?

Nordhavns traditionally have had a day tank setup. I was going through the specs on a new Nordhavn build and noticed the model I'm interested in has only one very large fuel tank and no day tank. Hummm.

 

[twistedtree]

Shall we take a step back and drift a bit? A few questions:

• What common problems does a day tank address?
• How large should a day tank be in terms of hours before hands on re-fill?

Nordhavns traditionally have had a day tank setup. I was going through the specs on a new Nordhavn build and noticed the model I'm interested in has only one very large fuel tank and no day tank. Hummm.

It's all about ensuring clean fuel.


The idea of a day tank is to run the machinery off an isolated supply of known-good fuel. To ensure it's know-good, fuel only get into the day tank by way of a filtered transfer system. Fuel is not allowed in via any other path since it might carry contaminants.


Purchased fuel always goes in one or more storage tanks where it is quarantined from the engines. It can be total shirt, but that can't get to the engines.


Even if you do have total shirt in the storage tanks, running through a water separating, 30 micron (give or take) filter will remove anything that could potentially stop the engines. Worst case is you need to change transfer filters while moving fuel, but the engines should remain safe and running the whole time.


As for size, there is really no hard rule. The trade off is how much time you spend filling the day tank. I don't see any down side to a large day tank, say one that can run the boat for a full 24 hrs or even multiple days. But I think more practically it will be less. I don't think I'd want to have to mess with it more than once every 6-8 hrs, and definitely not less than 4 hrs, or whatever your minimum shift time is. And don't forget that you want to fill before the tank get down below maybe 20%, and only fill to 80-90%, so allow some margin.


Nordhavn calls it a "Supply Tank" because on many models it's too small to be a useful day tank. On our 60, we took two of the small storage tanks and opened them to permanently gravity feed to the supply tank, and treated the three interconnected tanks as a single, large day tank. The deck fills for those tanks had never been opened when I sold the boat. It was 300 gal total and worked really well. We would fill when it got down to 60 gal or so, but there was plenty of slop if you weren't right on time. And we would fill to no more than 250gal, and often under 200 gal. When on a passage I would typically fill every 12 hrs, but we could go longer. It was nice to not have to be right on top of it.


I think the risk is that if you aren't minding the shop, you can perhaps more easily run the tank dry. We had the tank level alarmed at about 50 gal and the sound would wake the dead. My wife hated it when the alarm went off, so she ended up being the best alarm, "reminding" me to refill.


On our new boat I am making the supply tank a good bit larger than standard to make it an effective day tank. It will end up in the 175 to 200 gal range which should cover an 8 to 12 hr shift, depending on speed.

 

[sunchaser]

TT
Your rationale is logical. In far away iffy fuel places a day tank as you describe is an added level of comfort.

I know a few world cruisers (without a designated day tank) who try to keep one tank of cleaned fuel so that in the event of a bad load they have time to deal with it while underway. Then transfer newly delivered and filtered fuel to the "good" tank as it draws down.

We have one 100 gallon tank that is "internally" re-filtered frequently and serves as our safety supply. This tank is also our diesel heater cleaned fuel supply.

 

[twistedtree]

TT
Your rationale is logical. In far away iffy fuel places a day tank as you describe is an added level of comfort.

I know a few world cruisers (without a designated day tank) who try to keep one tank of cleaned fuel so that in the event of a bad load they have time to deal with it while underway. Then transfer newly delivered and filtered fuel to the "good" tank as it draws down.

We have one 100 gallon tank that is "internally" re-filtered frequently and serves as our safety supply. This tank is also our diesel heater cleaned fuel supply.

Sounds like a de facto day tank. What matters is that it accomplishes the goal of fire-walling good fuel from unknown fuel.

 

[angus99]

As I noted earlier, we use our third storage tank under the aft berth as a day tank. We run it pretty much as twistedtree described and only transfer filtered fuel to it from the larger saddle tanks. Not a big deal at all to run the transfer pump each morning to move a day’s worth of fuel while we do other chores. I’ll be putting the pump on a timer soon. One other thing we do is drain the day tank (transfer the fuel back to the sadlle tanks) before the boat sits for any length of time. Obsessive? Probably, but it works for us.

 

[stubones99]

I would say the most foolproof solution is having an overflow in the day tank back to the main tanks. Even if you have a problem with a timer, it simply cleans and overflows back to the main tanks.