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Old 19-10-2021, 02:04   #1
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Day / header tank versus polishing system

Hi all,

We have 1100 litres of fuel across two tanks and will be sailing into areas of questionable fuel quality. I'd like to either polish the two tanks with a fixed polishing system, or setup a day/header tank with filters.

For the purposes feeding our Cummins with pristine fuel, which is the better option? The day tank seems to have the most benefits, because it includes additional fuel visibility / consumption understanding + the the extra filtration of pre-filtering into the tank. However, it does add additional complexity to the system, and is also quite a bit of a job.

Fuel polishing alone seems good, however it seems that unless you have really really good pickup or run the system in rough weather you might just be wasting your time?
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Old 19-10-2021, 02:33   #2
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Re: Day / header tank versus polishing system

I'm not sure why you see these things as alternatives to each other.



If I thought I could not be sure of not taking bad fuel on board, I would do both.


You are right that fuel polishing is only as good as the pickups. If you don't have sumps in the fuel tanks, then maybe you can at least get the pickups lower than the consumption pickups. Then do your polishing when in a lively seaway.


Day tank will allow you to draw off fuel from the main tanks ahead of time, have a good look at it, assure yourself that it is good and clean, and then for however long your day tank lasts, you can relax. In my opinion it's a must have for any boat venturing into remote and undeveloped areas. But it's not enough by itself -- the day tank will allow you to detect a load of bad fuel before you start using it, but then what do you do?
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Old 21-10-2021, 21:13   #3
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Re: Day / header tank versus polishing system

You are right, they are not necessarily alternatives to each other. They are closely related though in terms of their primary function which is fuel hygiene.

I've decided to move ahead with the header tank install at minimum, using a FACET fuel pump through a 10 micron CAV filter setup, which pumps into a 70l poly tank above the engine block for gravity. This then feeds out into the existing CAV filter setup & inbound fuel lines.

I've got a nice little fuel gauge to put into the pilothouse instrumentation cluster and will mount a refuelling switch next to it, so you can refuel the header tank with easy visibility while underway.

I'll see how I go with a fixed polishing system down the track, if the header tank install doesn't kill me!
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Old 22-10-2021, 02:31   #4
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Re: Day / header tank versus polishing system

We have both a day tank and a fuel polish system. Both systems help deliver clean fuel to the engine, but it is difficult to quantify the benefits. My guess is that their contributions are similar. The ideal is both.

A fuel day tank needs a pump, filter, pick up and return to main tank to be installed, so when fitting a day tank you already have most of the requirements of a fuel polishing system. It only needs an extra couple of valves and you can have a basic fuel polish system.

This basic fuel polish system can be significantly improved by using a separate pick up at the very bottom of the tank and using a separate filter and pump so the polishing system is independent. These are worthwhile improvements to the polishing system.

However, a basic polishing system is still a help and I would at least add this facility to your day tank installation. It should be very little extra work to add this option.
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Old 22-10-2021, 04:01   #5
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Re: Day / header tank versus polishing system

Quote:
Originally Posted by noelex 77 View Post
We have both a day tank and a fuel polish system. Both systems help deliver clean fuel to the engine, but it is difficult to quantify the benefits. My guess is that their contributions are similar. The ideal is both.

A fuel day tank needs a pump, filter, pick up and return to main tank to be installed, so when fitting a day tank you already have most of the requirements of a fuel polishing system. It only needs an extra couple of valves and you can have a basic fuel polish system.

This basic fuel polish system can be significantly improved by using a separate pick up at the very bottom of the tank and using a separate filter and pump so the polishing system is independent. These are worthwhile improvements to the polishing system.

However, a basic polishing system is still a help and I would at least add this facility to your day tank installation. It should be very little extra work to add this option.

IMHO a fuel polishing system which does not pick up at the very bottom of the tank is not an actual fuel polishing system. If you pick up at the same place the engine does, you're only getting dirt and water which is already getting to the engine.



How much trouble is it to add just one pickup? Access can be an issue on some boats, but fuel polishing need not be expensive. A filter, an inexpensive pump, a pickup, some hoses, is really all there is to it. I would add a vacuum or pressure gauge to that to see how the filter is doing.


Note i don't have this on my boat, as we don't really have any significant fuel problems where I sail, and -- importantly -- my fuel fill is NOT located in the deck where water can get past the o-rings and into the fuel. Most fuel problem, I believe, occur as a result of deck-mounted fuel fillers, not fuel which is bad in the first place.


If you do have deck-mounted fuel fillers, be fanatic in keeping fresh o-rings on them and keeping them cinched down to the correct torque. Any slight deterioration of the rubber, or over- or under-torquing will let water in, and then you're screwed.
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Old 22-10-2021, 04:24   #6
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Re: Day / header tank versus polishing system

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Originally Posted by Dockhead View Post
IMHO a fuel polishing system which does not pick up at the very bottom of the tank is not an actual fuel polishing system. If you pick up at the same place the engine does, you're only getting dirt and water which is already getting to the engine.
Yes, a polish system with a pick up at the bottom of the tank is much better, but adding one is not always easy.

A polishing system with a higher pickup will be less effective particularly for eliminating water from the tank, but the polishing system will still be filtering and re-filtering large volumes of fuel, especially when the tank is stirred up underway. If nothing else, the large fuel volume will clog the polishing filter rapidly, so at least you will have some warning before the fuel becomes bad enough to clog the engine filter.

Quote:
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If you do have deck-mounted fuel fillers, be fanatic in keeping fresh o-rings on them and keeping them cinched down to the correct torque. Any slight deterioration of the rubber, or over- or under-torquing will let water in, and then you're screwed.
. The traditional flush deck fills on the side deck are a silly design.
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Old 22-10-2021, 04:28   #7
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Re: Day / header tank versus polishing system

What kind of pump do you use for the polishing system?
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Old 22-10-2021, 04:48   #8
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Re: Day / header tank versus polishing system

A very good article on fuel polishing by Steve D'Antonio.

In short, pump should sized large enough to create turbulence in the tank.

https://stevedmarineconsulting.com/f...ems-explained/

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Old 22-10-2021, 05:14   #9
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Re: Day / header tank versus polishing system

For menthe challenge of a day tank is assuring your pump can draw through sufficient head. My steel boats have the main tanks in the keel and the day tank fairly high up.

That portion of my brain where I store the name of my pump is in Covid lock down, info not accessible. Same type used to feed a diesel stove.

They work but are damn slow as the tank empties. I am not sure I can empty the tank.

Alternative suggestions viewed with gratitude.

But my point is, you need to look at the lift height and make sure your pump can accommodate that plus the loss through the filter.
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Old 22-10-2021, 09:27   #10
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Re: Day / header tank versus polishing system

Walbro, that is the make of pump I use.

Head can be extended by using a one way, ball valve.
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Old 22-10-2021, 10:44   #11
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Re: Day / header tank versus polishing system

I’m blessed with not just sumps in my tanks, but drains at the bottom of those as well, which I converted into the draw points of the polishing system.

That said, when you only have the regular pickup tube, I believe all of those are removable and you can simply add a little length of flexible fuel hose, just long enough to make a 90 degree bend when reinstalling the tube. Now you draw from the bottom.
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Old 22-10-2021, 11:55   #12
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Re: Day / header tank versus polishing system

Quote:
Originally Posted by mvweebles View Post
A very good article on fuel polishing by Steve D'Antonio.

In short, pump should sized large enough to create turbulence in the tank.

https://stevedmarineconsulting.com/f...ems-explained/

Peter
This ^ Most DIY polishing systems donít move the volume required to properly clean a tank. Buy a decent pre-filter for filling the tanks (donít let sh*t get in there in the first place) and install dual or triple racors, one off the tank and two interchangeable before the engine. The engine will generally provide a similar amount of fuel polishing as a small DIY polishing system.
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Old 22-10-2021, 12:31   #13
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Re: Day / header tank versus polishing system

Quote:
A fuel day tank needs a pump, filter, pick up and return to main tank to be installed,
John, is this really so? If one returns the excess fuel to the main tank, would this not empty the day tank too rapidly? I would have thought the return should go back to the day tank.

Jim
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Old 22-10-2021, 12:41   #14
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Re: Day / header tank versus polishing system

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John, is this really so? If one returns the excess fuel to the main tank, would this not empty the day tank too rapidly? I would have thought the return should go back to the day tank.

Jim
Ideally in my mind, engine return goes back to the day tank, but the day tank should have an overflow back to the main tank. That allows you to continually feed fuel through the filtration system to the day tank and allow clean fuel to return back to the main tank (providing some polishing effect). And it means you can't accidentally overflow the day tank and lose fuel overboard via the tank vent.
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Old 22-10-2021, 13:28   #15
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Re: Day / header tank versus polishing system

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Originally Posted by Jim Cate View Post
John, is this really so? If one returns the excess fuel to the main tank, would this not empty the day tank too rapidly? I would have thought the return should go back to the day tank.

Jim

Yes, as you correctly point out the return has to go to the day tank. However, as Rslifkin points out the overflow from the day tank should lead to the main tanks. This prevents fuel spill if you transfer too much fuel from the main tanks and it also allows the worthwhile option of running direct from the main tank without any overflow issues. In this case it functions as a return to the main tanks, which is what I was referring too.
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