TWL: Fuel Polishing

[Hendershot, Rob]

Forwarded to info@trawlerworld.com since 'captnwil@earthlink.net' appears to
be no longer valid. -Thanks.

>   -----Original Message-----
>  From: 	Hendershot, Rob
>  Sent:	Tuesday, January 21, 2003 10:03 PM
>  To:	'captnwil@earthlink.net'
>  Subject:	Fuel Polishing...
>
>  Capt'n,
>
>  Just wanted to point out a possible article issue and a special issue that
>  occurred on my boat that may be of interest to your readers, due to the
>  fuel tank installations.
>
>  In your article:
>
>  How To:
>
>  Captn Wil's Diesel Polishing System
>
>  By Wil Andrews
>  (http://www.trawlerworld.com/features_06.htm)
>
>  in the section Design Considerations you mention at the end "...filter
>  replacement intervals decrease."
>  "The common system with one secondary and one primary fuel filter tries to
>  keep the fuel that enters the injection pump just like new and the only
>  effect on the remaining fuel is the returned clean fuel. Once we
>  understand that most of our engines return very little fuel to the tank it
>  becomes obvious that this system has little or no effect on the fuel in
>  our tank. The fuel in the tank keeps getting less and less just like new,
>  and filter replacement intervals decrease."
>  I believe as the fuel gets older, the filters plug-up more often,
>  necessitating the need for more filter replacements. I also believe that
>  most installations possibly don't circulate the fuel very well. And in
>  fact, boats that simply run in-place (at the docks) or in flat-calms,
>  possibly accumulate old fuel in the back sides (away from the pick-up and
>  return plumbing) where baffling partitions off rear sections of a tank.
>  I too, just after hitting almost four years of owning my boat, plugged my
>  fuel filters. The coffee grind looking stuff just kept coming out of my
>  selected tank, even though some 'fresh' fuel was added only a few weeks
>  earlier. In the nearly four years of running my new-to-me boat I had kept
>  the fuel additives going into my tanks and never seemed to have any fuel
>  related problems.
>  One operational difference that I did start doing within the last two
>  seasons was to constantly top-off the boat with fuel. I did so in the
>  belief that I would help prevent condensation and water formation in my
>  tank. In fact, I have never seen any water accumulation in the filter /
>  separators (either before or after starting this practice).
>  But now --as Paul Harvey would sort-a-say, I have to tell you the rest of
>  my story.
>  My boat has four fuel tanks. Two tanks starboard and two port. The front
>  tanks are fifty gallon tanks and the aft tanks are thirty gallons. Each of
>  the two tanks on each side are connected as a common tank with about a
>  one-foot run of 1-1/2 hose connecting an aft tank to a fore tank. This
>  gives a total of eighty gallons on the port side and eighty gallons on the
>  starboard side, leading to a total fuel capacity of 160 gallons for the
>  boat.
>  As the layout would have it, the front tanks are considerably lower than
>  the aft tanks. Both the front and aft tanks have the same depth, but the
>  top of the front tank comes up to approximately half the height of the aft
>  tank. This makes the aft tanks about 1/2 capacity higher, or 15 gallons,
>  higher than the fore tanks.
>  Now to the gritty details (pun intended).
>  The fuel pick up and the fuel return on this system is located on the very
>  most forward position of the forward tanks, where the forward tanks are
>  just behind the bulkhead for the engine room. I select either to run off
>  the port common tanks or starboard.
>  Being the intelligent person that you are, by now you have most likely
>  figured out the big problem with my system! But just in case, I will
>  continue.
>  When I started my practice of "keep-the-tanks-full", I never ran fuel out
>  any where near the halfway mark on the aft tanks. At best guest, the fuel
>  in those aft tanks have gotten about two seasons old.
>  And it then all happened last Sunday while whale watching. As the forward
>  fuel tank emptied to just below the 60 gallon mark, for the first time in
>  quite a longtime, the slime of coffee grinds slid all the way down and to
>  the front of the forward tank that was selected and, poop, I plug my
>  number one primary filter to the point no  more than about 1000 rpms could
>  be obtained. (Or as Marvin Zendler [sp?] "Channel 13, Eye Witness News"
>  would say --with a southern-draw, "Slime in the Ice Machine!" I am not
>  sure if you know about this Houstonian, but to say the most, he was the
>  fellow connected to the Chick Ranch controversy in La Grange, Texas.)
>  No problem I though, and I switched to my second primary filter, which
>  before it was selected, had a very clean bowl with nice wine-colored fuel.
>  Within about 30 seconds (note that the throttle setting was somewhere near
>  WOT, but engine rpm before the switch was much less than half WOT rpms)
>  the entire bowl filled with goop and the filter plugged to the point the
>  engine stopped in a few minutes.
>  Note that this is pure speculation. I didn't actually see any
>  goop-plugging substance actually slide off the bottom of the aft tank. It
>  is possible the forward and aft tanks are of a equally nasty state. But
>  the other side of the boat's tanks still have enough fuel to not empty out
>  the aft tank. I was able to pull clean fuel out of the other side. I bet
>  that when I have consumed enough fuel form those tanks to empty the aft
>  tank (this will happen at about 80 - 1/2(30) or 65 gallons --remember the
>  aft tanks are about 15 gallons higher than the forward tanks), goop with
>  hit again.
>  And now the end of my story. I will reengineer the return lines to return
>  fuel to the aft tanks and I will add a fuel-scrubbing-recirculator system.
>  This system will pull fuel from the forward tank pickups and return fuel
>  to the aft tanks. And as suggested, the pull and return will be on the
>  same common tanks, such as the port or starboard tankage.
>  Otherwise, I will have to wait until the whales go home to have a clean
>  tank of fuel and a return of my "safety-factor" (as apposed to a
>  "fear-factor"!).
>  BTW, I am thinking I will discontinue the use of that very expensive
>  bottle of "X" stuff.
>  Rob Hendershot
>  Onboard "China Doll"
>  1984 Passport 51