My take on DIY fuel polishing system (15 Gal per min)

[Delfin]

Sailorcraig. As you can see there are many fans of fuel filtering systems and they are entitled to their opinion.
First fuel tanks need to have both a drain and a fuel pickup from the very bottom of the tank. You never see a truck stuck on the side of the road with diesel bug problems because every truck takes it's diesel from the bottom of the tank the same as your car/pickup.
If you have recently filled with fuel, if possible allow it to sit for 24hrs, then take a small glass and 'crack' (slightly open) the valve at the bottom of your tank and allow a trickle of fuel into a glass jar. If you see water then very slowly continue to drain until its pure diesel.
Where does the water come from ? The most likely culprit is condensation on the inside of your fuel tank !
The ideal is to have a fitted bolted hatch on the top of your tank where you can drain off your fuel and wash out the tank with parrafin before returning clean filtered diesel. By drawing fuel from the very bottom of the tank any microscopic particles will be drawn into your primary filter as the engine designs are mean to. These filters are changed as part of your regular servicing schedule.
A simple Caterpillar primary filter with an integral centrifugal water separator is perfect for the job, a quick visual check in the glass bowl at the bottom of the filter will see if there's any water, simply open the drain tap on the bottom of the filter, drain the water off and the jobs done.
I've nothing against Raccor but they are expensive, uneccesary and each connection is a possible point of air induction.

One difference between over the road trucking and many trawlers is trucks burn through their fuel daily from a single or double tank, and some trawlers take a year to do so, out of many tanks, like mine. The former doesn't need a polishing system, but I sure do.

As noted elsewhere, I picked up fuel in Hawaii with a load of contaminants in the 2 - 10 micron range, which plugged the Cat 2 mic OEM filter since the ore-filters were all 20 micron. The only way I made it back to the PNW was by polishing the piss out of the fuel by running my polishing system 24x7, and manually cleaning the Racor pre-filters. And yes, I should have had more OEM filters than I did, but lacking that foresight, the polishing system got us back. As should be obvious, draining a couple ounces of fuel from a tank drain would not have been of any value.

 

[SoWhat]

I’m looking at a trawler that has been used very little for several years so I’m going to assume the diesel tanks have sludge build up. Will continuously polishing over time clean this built up sludge or am I into cutting ports to get inside to scrub?

I would not assume anything. Put a borescope down fill tube and take a look at bottom of tank.

If there is sludge you would have to get it back into suspension in order to get it through polisher. Not sure how you would do that. Best solution would be to store fuel in 55 gal drum, cut cleanout in side of tank, and manually clean bottom.

My boat was inactive for many years. zero sludge.

 

[sunchaser]

I’m looking at a trawler that has been used very little for several years so I’m going to assume the diesel tanks have sludge build up. Will continuously polishing over time clean this built up sludge or am I into cutting ports to get inside to scrub?

How old is the boat? If dating back to the 80's with higher sulfur fuels there may be some worry ---- but dip the tanks and observe the Racors as Ted says and if no crud you should be fine.

We sold our DF with us being the only owners for two decades. The tanks were quite clean with nary a sign of crap, crud or water appearing in the Racors. Dipping the tanks to the bottom showed the same.

 

[Lepke]

My current boat sat for 6 years with no care, no mothballing, but it had Detroit Diesels - the main reason I bought it. The main tanks were not accessible without destroying the galley.
I put in a 3x dose of algae-x and added 20 gallons of new fuel to the 50 gallons in the day tank. The DD naturals pump 70 gallons an hour at cruising, so the fuel was filtered several times. When I fueled the main tanks I added the same dose of algae-x. After the first tanks loads I went to 2 micron filters. I use a fuel conditioner every fueling. I use Archoil now.

Much later when I redid the galley I got to the main tank tops. 3 tanks are about 4'x5'x6' high. I pumped them dry and went inside. No water no sludge.

Always carry extra fuel filters.