FUEL POLISHING SUGGESTION                    Dick Stevenson, s/v Alchemy
The following was written for a specific boat (a Valiant 42), but variations on the basics below make polishing fuel possible on any vessel. The one challenge is getting some sort of pick-up to the bottom/low corner of the tank. If one is building new tanks, a fuel polishing pick-up going to the bottom low corner (below the engine pick-up tube) should be considered.
Fuel polishing serves at least 2 functions: good fuel to the engine and, secondarily, to keep accumulated water and yuck (technical term) from attacking the tank itself and shortening a tank’s life. Many owner-designed fuel polishing draws through the pickup tube which leaves the bottom of the tank untouched. I was lucky as Valiant 42s (like Alchemy) with saddle tanks, it is possible to get to the very bottom through the connecting fitting between tanks. It is relatively easy to tap into this connection to draw fuel from below the pickup tube. All other boats must figure a way to get to the bottom of the tank, usually possible, but often demanding some creativity: worth the effort.
Fuel Polishing for Alchemy, V42-128, with saddle tanks
What I like about this system is that it covers both polishing the fuel and getting crud/water and any loose stuff from the tank bottoms below the pick-up tube. It does not, however, get inside the tank and scrape the sides etc., but the extra cleaning suggestion below does a bit of that.
Alchemy’s saddle tanks are great in that they have a nipple on each tank at their lower end. The 2 tanks on each side are connected to each other from these low nipples with a valve in between. I broke into the hose near the lower nipple, attached a “T” and added a valve onto the T with a hose fitting.* I now have access to the fuel from the bottom of each tank. The lower tank is of course the more important as stuff migrates there. I did this both port & starboard. There are 2 tanks on each side of a 42 w/ saddle tanks (4 altogether) right next to each other fore and aft. (there are 2 per side to get them into the locker through the hatch: a nice touch as too many boats seal their tanks into the boat when they put the deck on).
The “polisher”
I then mounted an old Racor filter assembly (if possible, use the same filter as used on the boat) with hoses and a fuel pump on a board with a cigarette lighter attachment for power for the fuel pump. (Remember, you want to draw fuel through the filter, not push.)
The following pertains to my boat: other must attach the polisher assembly to allow them to draw off the bottom. I attach the intake hose to the “T”ed off valve fitting and put the outlet into the deck fill. Open the T valve and you are pumping off the bottom of the tanks. Close off the upper tank with the Valiant built in valve and you are only drawing off the lower tank in the corner where crud/water accumulates.
How often?
We do an hour or two of polishing each side every 2-3 months during the season (or sooner if concerned I have gotten bad fuel). This runs about 17 gal. (1/3rd of the tank capacity) through the filter in each tank which I have been keeping at 10 micron. I take from the bottom and put into the top unless I am emptying a tank for the winter.** We can also pump from drums and guarantee that the fuel from the drums is clean before it gets into the tanks.
Extra tank cleaning
This is for Valiant 42s and can be accomplished by disassembly of the valves etc. at the base of the tanks. Remove the lower nipple and there is a nice, not big, but nice size hole in the tank wall. Take a dowel with rag sections attached (electrical ties or just tied on) and insert and scrape. Continue as needed. Tedious but does get some yuck. And with a bit of a right angle insert you can get right in the corner.
*Something I recommend in V42s is a simple plywood partition protecting the valve/hose assembly at the base of the tanks from lines etc. that may be stored in the locker. These could get caught on the valves/hose and inadvertently pulled damaging these connections.
**The pump also acts to transfer fuel. I usually empty one tank each winter (into the other) to have Alchemy sit higher in the water. I have found that an empty tank will not collect water over a winter in the Med or in the UK.