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Old 20-09-2010, 12:35   #1
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Diesel Fuel Tank Management

The boat has two equal-sized fuel tanks which together will provide about 300 hours of cruising-speed propulsion. The boat will usually be operated 10 hours a week, so full tanks would last 30 weeks (more than seven months).

So, what is the best tank-management strategy to minimize fouling the diesel fuel and filter? Keep both tanks topped off (refuel every month)? Keep one tank empty and not refill the other tank until nearly empty? Consume one tank until completely empty and then draw down from the other tank? Help!
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Old 20-09-2010, 12:55   #2
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Fouling of fuel happens due to water in the tank. I have sumps, low spots, in the tanks with valves at the bottom of the sumps. I periodically connect a pump to the valves and circulate fuel through Racor water separator/filters and back to the tank. This eliminates any possibility of having bugs in the fuel.

Keeping tanks full will reduce the amount of condensation, but will not eliminate it entirely.
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Old 20-09-2010, 13:08   #3
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Keep your tanks full and make sure you use both tanks. Provided you tanks are clean to begin with and there is no way for water to leak into the tank you should be ok. I would also recommend that both tanks have their own fuel filter systems. By the way clean means clean not fuel polished clean.
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Old 20-09-2010, 13:12   #4
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Unless you are planning a long trip and need the extra fuel, there is little point in keeping both tanks filled. You should leave one empty and draw off the other. I would choose whichever of the two has least effect on trim to use on a regular basis. It is always best to keep tank topped as that helps minimize condensation. I usually top off with 20L jerry cans as needed.
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Old 20-09-2010, 15:03   #5
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Install a fuel polishing system now while in the building stage. Do it correctly and It shouldn't matter if you fill the tanks or not but I would fill them and polish after every fuel addition, and every few weeks while underway. If the tanks are low the fuel will add ballast.
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Old 20-09-2010, 16:13   #6
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A diesel engine is a self-polishing system as the fuel returned to the tank has passed through the primary and secondary filters. As long a the fuel was clean, and is used in a relatively short time, I would not bother with a polishing system on a cruising boat. If, on the other haand, the fuel sits in the tank forever, then water from condensate + algae growth in that water will become a problem. I would spend money on a two filter manifold rather than a polisher.
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Old 20-09-2010, 16:45   #7
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I would still add a few good centrifugal filters between the tanks and the engine at least, if not a full polishing system. One can never be sure of quality of fuel at different points, so it would not hurt to keep the primary diesel filters from being overwhelmed.
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Old 20-09-2010, 17:00   #8
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A diesel engine is a self-polishing system as the fuel returned to the tank has passed through the primary and secondary filters.
No, that can't be classed as self polishing. A fuel polishing system has to pump enough fuel to stir up the tank and move the crud through the polishing filter. The little fuel pump on an engine certainly can't do that.

A fuel polishing (cleaning) system should be completely separate from the engine fuel system. The engine fuel system still needs good filtering, but the lines and filter will be sized smaller than the fuel polishing system.

Do a little research. Check out some of Steve D'Antonio's work on fuel polishing in Passagemaker magazine. There is a guy that writes about what he knows and he has the experience to be believable.
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Old 21-09-2010, 16:22   #9
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I have just come across some pictures on Maine Sails site on the installation of his fuel polishing system, along with his new fuel tank. They can be seen here
Compass Marine Project Articles Photo Gallery by Compass Marine at pbase.com

Its the last section on replacing fuel tank.
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Old 21-09-2010, 16:57   #10
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Google Soltron (Xbee in Europe) simply use it to keep fuel tanks clean all year.
It works. Have used it 6-7 years now.
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Old 30-09-2010, 11:55   #11
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Prevent rather than recover

Some interesting things learned from Parker, the manufacterer of Racor filters.
Diesel fuel will absorb small amounts of water and hold it in solution.

The amount of water that will remain in solution is dependant on temperature.

On a daily basis fuel tanks warm and cool. As the fuel cools a small amount of water will fall out of solution.(depending on humidity etc)

Racor filters can collect the smallest bits of water when the fuel is fed through at a very slow rate.

Parker is recommending that a slow flow (oz/hr) be pumped through racors in the evening as the tank cools.

Using this protocall there should never be any accumulation of water in the tank and no algae.

The only posible fuel treatment would be a solvency addative to minimize varnish formation and if you have a mechanical diesel maybe a cetane improver.

I like this idea a lot but my fuel turnover is high enough to not bother.
Parker does make the pump, a crystal driven diaphram pump that uses so little power, you can leave it on.

The idea here is to keep the fuel dry, by any means. With dry fuel a polisher is never needed.
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Old 30-09-2010, 20:30   #12
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Pay attention to how the fuel return from the engine is set up. If it returns to only one tank and that tank is closed and you draw from the other you could overfill the closed tank and spill fuel out the vent.
I keep both tanks full and open.
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Old 07-10-2010, 12:46   #13
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Originally Posted by Highlander40 View Post
Some interesting things learned from Parker, the manufacterer of Racor filters.

...

The idea here is to keep the fuel dry, by any means. With dry fuel a polisher is never needed.
Very interesting concept!
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Old 07-10-2010, 12:52   #14
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Open the tanks up and clean them out. With a clean tank, clean fuel, and approved additives you don't need to polish your fuel. And if you do need to polish your fuel, you probably really need to clean out your tank. Either way, keeping your tank clean (via some paper towels and visual clean out) isn't much work and solves the problem at the source.
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Old 07-10-2010, 12:57   #15
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Here's some gunk I scraped from the sides of my tank:



all the pictures:

cleaned out the fuel tank - TheKeel.com

It's my little opinion (and I'm far from a diesel expert) that no matter what you do, eventually you will need to clean out your tank because there's no way that circulating fuel around (polishing) is going to get the gunk off the walls. You can do things to keep gunk off the walls, but no one is going to promise you that if you do x, y, and z that you'll never have to clean the tank.

And if you have a clean tank and clean fuel, why are you polishing?

Polishing just seems like a way to make money on people without actually solving the problem.
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