PRACTICAL
Keen to eradicate all traces of diesel bug after installing
a new stainless steel tank, John Mimpriss fi ts a fuel
polishing loop to his Moody 34
Onboard diesel
polishing
T
he article about
diesel polishing in
November’s PBO,
written by Damian
Walker, touched on
a subject very close to my
heart; namely, clean fuel. My
passion for clean fuel started
about 18 years ago, during
a return trip from the West
Country in my Moody 34.
En route, I found that I had
picked up some dirty fuel, which
manifested itself halfway across
Lyme Bay. We managed to get
back to Gosport having drained
out the worst from the bowl of the
inline fi lter, and changing both that
and the engine fi lters. On return,
I inspected the inside of the tank
and was horrifi ed at what I saw.
The interior of the mild steel tank
was covered in curtains of slime
and there was plenty of sludge
and mess at the bottom of the
tank; the exterior also showed
signs of rusting. The upshot was
that, rather than cleaning and
treating the existing contamination,
I opted for a new bespoke stainless
steel tank made to my dimensions.
Unlike the old tank, where
the fuel was sucked through a
stack pipe, my new tank was
constructed with a V-shaped
sump with a drain-off at the lowest
point and fuel fed to the engine
from a tapping in the wall of
the tank above the sump. The
intention was to ensure that fuel
could still be fed to
the engine under
gravity alone if the
engine-driven lift
pump should fail.
A stopcock on this
pipe enabled fi lter
changing without
losing fuel into the
bilge. An inline
30-micron fi lter with a
bowl and water drain was fi tted
in the fuel line between the
tank and the integral engine
5-micron fuel fi lter.
As a matter of routine I added
anti-bug additive whenever I
refuelled, and I tended to keep the
155lt tank at least half-full in the
season and full over the winter.
Also, twice a year I would drain off
from the sump of the tank and
continue until I achieved clear
fuel. Until two years ago I was
draining about 2-3lt each time,
but in March 2014 I found serious
quantities of water and sediment
and had to drain off nearly 25lt!
Having confi rmed that water
was not entering through the deck
refuelling fi tting, I continued my
six-monthly routine, but was
concerned to note that it was now
averaging about 10lt drain-off to
get clear fuel every time.
So, I wrote to PBO expert Pat
Manley and asked him if I was
in fact being overzealous and
wasting good fuel – especially
since throughout this period I’dnot seen any sign of
contamination in the inline fi lter
bowl. His response was very
supportive, and he went further by
commenting that the increase in
biodiesel as an additive to marine
diesel had increased the risks of
water absorption and, as a result,
diesel bugs in the fuel tank. His
reply started me thinking about
how I could obtain clean fuel in a
more effi cient and environmentally
acceptable manner.
Having done some research,
I found a very useful basic fuel
polishing system on the website
of ASAP Supplies which included
an itemised list of all the required
components – down to the last
Jubilee clip! I could have just
gone for a simple solution by
incorporating an additional fuel
fi lter (Racor turbine type) in my
existing engine fuel supply line,
but that would have meant thatthe operation of the fi lter was
reliant on the engine running.
So I opted instead to install an
onboard fuel polishing loop. I was
lucky as I could use the existing
sump drain outlet in the fuel tank
as a supply and connect into the
engine 8mm fuel spill return line
running to the top on the opposite
side of the tank.Fitting the loop
Having decided on my
plan, I purchased the
following components:
One Racor 500FG diesel
turbine fuel fi lter (10-micron) withABOUT THE AUTHOR
Retired after a career as a pilot, John
Mimpriss was introduced to sailing aged 8,
crewing on his uncle’s East Coast- based
Vertue. Since 1960 he has sailed either by
chartering or on his own yacht. Yachtmaster
qualifi ed, John has owned his Gosport-
based Moody 34 (Lonk Avel) since 1997.(^76) Practical Boat Owner 593 November 2015 http://www.pbo.co.uk• Practical Boat Owner 593 November 2015 http://www.pbo.co.uk• (^77)
Diesel polishing
PRACTICAL
ABOUT THE AUTHORDamian Walker is a recently retired flying
instructor and aerial photographer. Having cruised for 3,000 miles, he has passed Yachtmaster theory, Day Skipper practical
and first aid, and may now have the time to do more, health permitting.and RYA certificates for radar, diesel CEVNI
T
fast approaching and the nights were he end of another windy summer was
longer, but I reasoned that there would be an opportunity for one more single-handed trip in getting noticeably
my Colvic Watson motor-sailer, before the season ended. I had planned to motor-sail northwards Delta,
from Lowestoft and revisit myfavourite place, Whitby, stoppingalong the way at Wells-next-the-Sea, Grimsby and perhaps (^)
Bridlington and Scarborough.had been choppy, uncomfortableand tiring, and I accepted an offer The 12-hour passage to Wells (^)
went alongside the visitor pontoon.from the Beach Patrol RIB to guideme into Wells Harbour, where IAfter a good night’s sleep, I was^
just about to cast off, havingunplugged the electricity cable,when the engine stalled. It would (^)
not run for more than a few seconds at a time, and then onlywith the throttle near wide open. I was unsure whether it was just fuel
starvation or perhaps an air leak. Iquickly reconnected the electricity supply to keep the battery
were only providing an amp or so. Imanaged to change the Champion filter for a Crosland as the 5-micron charging: the two solar panels
Champion seemed to clog easily.At last I was happy to leave,
‘Smaintains Damian Walker, whose hiny diesel is happy diesel’,
engine stoppage woes were cured by diesel polishing
Diesel
polishing
relying on being able to switch to the second filter as I approached Grimsby if there was any sign of
fuel starvation.Lowestoft Yacht Services when theengine had stopped just as I was A few weeks earlier I had visited (^)
approaching their service berth. That failure was also due to a dirtyChampion L131 5-micron fuel filter.
I isolated that filter, cleaned thebowl and replaced the three in-line filters, one on the engine and thetwo set for changeover in the event (^)
of a blockage. I considered myself fortunate that after fitting anothernew Champion filter the fuel filled
the bowl under gravity from 30-something-year-old stainless steel tanks, and the CAV filter needed minimal bleeding to Delta’s
remove residual air. The enginefired up again and ran sweetly as I returned to my mooring in Lowestoft Haven, so when
planning my late holiday trip north I was confident that I had threeclean and new filters.
morning again while I was attempting to I arrived in Grimsby on theSunday night, but on the Monday Delta’s engine stopped^
move position on the moorings. Iattempted a restart, and the engine started for just enough time with
the throttle wide open to attain a high rpm and rapidly switch from forward to aft gear before it failed again. I lifted the starboard floor
panel, reached down and switchedto the spare filter, and after areasonable but shaky start it ran
for some seconds at high rpm, whereupon the fuel lines werereplenished with fuel. I was stillunsure if there was an air leak as (^)
it had started after the overnight rest, but again only ran for a short while. I managed to change
moorings with the aid of some typically friendly berth-holders, and settled down to work out how to cure my now obviously serious
an engineer called Fozzie, who fuel problem.I was given contact details for
generally did work for visitors withboat problems and had a good record of problem solving. Heoffered me the use of a pump to
empty the tanks via the fuel sender opening, but I declined until I knew the extent of the problem facing
me. I knew for sure that I had twointerconnected tanks with around300lt in total of dirty diesel that had been standing for nearly two (^)
years owing to essential repairsthat meant the boat had been forced to stay on the hardstanding.
I’d had the foresight to add a bottle of Marine 16 diesel bug treatmentPolished performance
in 2011 after buying the boat andsome Marine 16 fuel stabiliser in 2013 during winterising. I knew that the tank sides were not polished
and smooth after fitting a standpipe for the Eberspächer afew weeks earlier, which required a (^)
hole to be cut in the top of the tank: when I inserted the standpipe it had touched the side of the tank, which felt ‘furry’. My response on
filter just for the heater’s newly re-piped supply, although in that occasion was to fit a separate^
hindsight that was a hasty action and not a solution. It wassuggested that I should discard the fuel, steam-clean the tanks
and start again, but that seemed excessive. I searched online for fuel containers, but decided thiswas too lengthy and expensive a
stainless steel: I was willing to fitsolution, and not really feasible inmy situation.The tank lids were made of^
the innovative Wema tank lids fromTek-Tanks, but was worried aboutwhat I might find under the plates if (^)
the orifice was not a 112mm roundhole, and the six plates appeared to be screwed into place withSikaflex sealing compound. I
believed that I needed them to stay sealed, at least until I got back tobase in Lowestoft. Next, I searched (^)
found nothing directly relevant tome, given that I was not a bulk Google for advice about dealing with fuel tank contamination, but
fuel user with 1,000lt tanks, norwas I presenting a significantenvironmental hazard.
that, although I had heard it before,meant little to me. Only two weekspreviously, Andy – a visitor to However, I came across a term (^)
The blocked filter
A filter bowl cracked during the 101-mile motor-sail home
After this bottle of contaminated fuel had settled overnight, a heavy layer of dead diesel bug was apparent: some of it remained in suspension, giving a darkened, cloudy appearance to the red diesel
I replaced the pretty clean Crosland filter with this Fram filter
PBO verdict
A good investmentTo build a DIY system, a small
diesel polishing filter with a140lph circulating pump canbe bought online for less than £100: professional systems (^)
can cost in the region of £500,but would seem to be a good investment even at commercial
a small solar panel connectedto the pump should suffice to protect the fuel over the winter prices. I have been advised that
when moisture allows thebacteria to grow rapidly. was initiated when biodieselThe diesel bug problem (^)
began to be added to the fuel back in 1998. Biocides like Marine 16 products quickly kill (^)
the bugs, which then coagulate and stay in clumpsin suspension but in a low
when the engine is not running,layer in the tank. The answerquite simply is a turbine filter with a pump for use especially^
and maybe when any fuelsediment has been stirred up.It seems obvious now that
a blocked filter will almostinevitably result in an enginestoppage unless the fuel is cleaned. When in the RAF, (^)
my flight sergeant in basic training used to say ‘shinyshoes is happy shoes’:
and ‘shiny diesel is happy diesel’ is equally applicable.
Delta, Damian Walker’s Colvic Watson motor-sailer
Watson – had shown me his comprehensive enginemanagement systems including aLowestoft on another Colvic
fuel-polishing filter. I had not reallygrasped how this could be such a critical part of the overall fuel
management system, but was beginning to realise the truth of it. Isearched online again and found the family-run business http://www.
to help me, and drove down from dieselpolishing.co.uk: the company’s Allen Blake (a friendlyYorkshire boat owner) was willing^
his base near Leeds. He twice filtered the entire dirty contents of my tanks with the system pictured
below, agitating the contents with the returning fuel over a period of four hours. The black sludge-likelayer at the bottom of the tank had
settled somewhat over 48 hours but only contained mostly dead diesel bugs that had coagulated
and made the filter bowl looklike a shaken snow globe, except (^)
The system shown here was used to twice filter the entire dirty contents of my tanks
with black snow falling.removed, although not all at once as the filter in Allen’s system would The black stuff was easily
have been blocked quite quickly. A tiered approach gradually cleaned it up. We only had to discard 9lt of
seem to be much water in it.liquid, and some of that could havebeen recovered or recycled if we’dhad more time as there did not^
300lt of shiny red diesel back in my tanks again and ready to flow After only four hours’ work I had^
through yet another new filter, aCrosland one this time. I motor-sailed the 101 miles back to base,stopping the engine after 20 hours (^)
that a filter bowl was cracked and and 20 minutes with plenty of diesel left in the tanks. I found
went to ASAP Supplies for a replacement, changing the pretty clean Crosland filter for a Fram. Now, the only weak point left in the
fuel system is the banjo bolt on the top of the Iveco engine-mountedfilter, and that is on order.
The bottom of the tank, showing the supply from tank to engine sited
above the sump outlet that feeds into the polishing loop