Filling the fuel tank for lay up


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Philip Heaton
Philip Heaton
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Having co-authored the anthology of erudition that is the OCC Practices Guide to Laying-up, I now have a question re the received wisdom on completely filling the fuel tank over winter in a Mediterranean-type climate. Clearly the issue is condensation but while I understand it in colder climes, just what are the risks??
Dick
Dick
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Philip Heaton - 10/20/2019
Having co-authored the anthology of erudition that is the OCC Practices Guide to Laying-up, I now have a question re the received wisdom on completely filling the fuel tank over winter in a Mediterranean-type climate. Clearly the issue is condensation but while I understand it in colder climes, just what are the risks??

Hi Phillip,
The following is mostly for in water storage or living aboard while over-wintering as we did for many years.
I experimented with mostly empty tanks (kept enough for heating) over wintering in the Med and in England, probably 6 winters in all split between each area.
I think there is nothing “wrong” with having full fuel tanks sitting for 6 months as long as the fuel is properly stabilized and “bio-cided” and the fuel is of good quality: having good filters helps.
That said, I carry 90 gallons of fuel on a 40-foot hull and I really like sitting high in the water when the boat is just sitting for 4-6 months (I also empty the water tanks and use “shore water”—see my write up of doing so in the Forum). This keeps the water-line from being a disaster at the end of the winter.
My tanks are high up on the sides of the boat where they are subjected to wider temperature fluctuations. I would think tanks in the bilge where water temps would make for little temperature fluctuation would make a difference: less condensation.
At no time did I find accumulation of water in the tanks as shown by water appearing in the water separating filters.
So, from my experience on my boat (Valiant), I see the warnings of water accumulation in the tanks over a winter in empty fuel tanks a “marine myth” (one of many).
So, my experience indicates no risk in empty tanks, especially with proper filters as mentioned above.
RC Collins (superb series of marine articles https://marinehowto.com/) did an experiment in the much colder clime than I experienced (Maine) and reported no condensation, but I was unable to find it on his site: he can be contacted if interested.
Come back with questions/comments.
My best, Dick Stevenson, s/v Alchemy

Philip Heaton
Philip Heaton
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Dick - 10/22/2019
Philip Heaton - 10/20/2019
Having co-authored the anthology of erudition that is the OCC Practices Guide to Laying-up, I now have a question re the received wisdom on completely filling the fuel tank over winter in a Mediterranean-type climate. Clearly the issue is condensation but while I understand it in colder climes, just what are the risks??

Hi Phillip,
The following is mostly for in water storage or living aboard while over-wintering as we did for many years.
I experimented with mostly empty tanks (kept enough for heating) over wintering in the Med and in England, probably 6 winters in all split between each area.
I think there is nothing “wrong” with having full fuel tanks sitting for 6 months as long as the fuel is properly stabilized and “bio-cided” and the fuel is of good quality: having good filters helps.
That said, I carry 90 gallons of fuel on a 40-foot hull and I really like sitting high in the water when the boat is just sitting for 4-6 months (I also empty the water tanks and use “shore water”—see my write up of doing so in the Forum). This keeps the water-line from being a disaster at the end of the winter.
My tanks are high up on the sides of the boat where they are subjected to wider temperature fluctuations. I would think tanks in the bilge where water temps would make for little temperature fluctuation would make a difference: less condensation.
At no time did I find accumulation of water in the tanks as shown by water appearing in the water separating filters.
So, from my experience on my boat (Valiant), I see the warnings of water accumulation in the tanks over a winter in empty fuel tanks a “marine myth” (one of many).
So, my experience indicates no risk in empty tanks, especially with proper filters as mentioned above.
RC Collins (superb series of marine articles https://marinehowto.com/) did an experiment in the much colder clime than I experienced (Maine) and reported no condensation, but I was unable to find it on his site: he can be contacted if interested.
Come back with questions/comments.
My best, Dick Stevenson, s/v Alchemy

Hi Dick
Thank you. Your comments are much appreciated and as always you seek to clothe ideas with facts and practical experience.
The reason I asked the question is that we have a half-full tank of diesel and normally I leave it full. We were about a mile off the entrance to the marina at Licata, Sicily (our winter in-water berth) when the engine cut out. We have dual Racor pre-filters, so quickly switching to the known-to-be-clean filter and checking that diesel was coming through to the engine, we restarted and ran OK. However, the bowl on the unco-operative pre-filter was full of the most awful tarry substance.  So we appear to have the bug.  I sloshed in 200ml of Marine 16 Diesel Bug Treatment (for about 180 litres of diesel) but have also decided to install a Marine 16 Diesel Dipper. I will need space above the level of the diesel in order to catch the swarf and the disc of aluminium when I cut a hole in the tank for the suction pipe, so I will be leaving the tank part-full for a couple of months and then return to the boat in January to do the job. 
I don't think things will be worse and I will probably give the diesel a second dose of Diesel Bug Treatment.
In the 13 years that we have had the boat, we have had a blocked pre-filter on three occasions: first in 2007, inside the marina in Bangor, Northern Ireland when the wind gently blew us into a vacant berth, then in 2014 when in the very narrow channel entering the marina Boat Lagoon in Phuket, Thailand and now just off the marina at Licata - three times lucky to get away with it .... and I cleaned out the tank thoroughly on the previous occasions and again in 2017 when in Trinidad and installing a replacement fuel guage sender. 
My wife, Norma, is getting very fed up with this as it takes her ages to clean up her electric toothbrush after I have used it in the nooks and crannies of the tank ...
Dick
Dick
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Philip Heaton - 10/22/2019
Dick - 10/22/2019
Philip Heaton - 10/20/2019
Having co-authored the anthology of erudition that is the OCC Practices Guide to Laying-up, I now have a question re the received wisdom on completely filling the fuel tank over winter in a Mediterranean-type climate. Clearly the issue is condensation but while I understand it in colder climes, just what are the risks??

Hi Phillip,
The following is mostly for in water storage or living aboard while over-wintering as we did for many years.
I experimented with mostly empty tanks (kept enough for heating) over wintering in the Med and in England, probably 6 winters in all split between each area.
I think there is nothing “wrong” with having full fuel tanks sitting for 6 months as long as the fuel is properly stabilized and “bio-cided” and the fuel is of good quality: having good filters helps.
That said, I carry 90 gallons of fuel on a 40-foot hull and I really like sitting high in the water when the boat is just sitting for 4-6 months (I also empty the water tanks and use “shore water”—see my write up of doing so in the Forum). This keeps the water-line from being a disaster at the end of the winter.
My tanks are high up on the sides of the boat where they are subjected to wider temperature fluctuations. I would think tanks in the bilge where water temps would make for little temperature fluctuation would make a difference: less condensation.
At no time did I find accumulation of water in the tanks as shown by water appearing in the water separating filters.
So, from my experience on my boat (Valiant), I see the warnings of water accumulation in the tanks over a winter in empty fuel tanks a “marine myth” (one of many).
So, my experience indicates no risk in empty tanks, especially with proper filters as mentioned above.
RC Collins (superb series of marine articles https://marinehowto.com/) did an experiment in the much colder clime than I experienced (Maine) and reported no condensation, but I was unable to find it on his site: he can be contacted if interested.
Come back with questions/comments.
My best, Dick Stevenson, s/v Alchemy

Hi Dick
Thank you. Your comments are much appreciated and as always you seek to clothe ideas with facts and practical experience.
The reason I asked the question is that we have a half-full tank of diesel and normally I leave it full. We were about a mile off the entrance to the marina at Licata, Sicily (our winter in-water berth) when the engine cut out. We have dual Racor pre-filters, so quickly switching to the known-to-be-clean filter and checking that diesel was coming through to the engine, we restarted and ran OK. However, the bowl on the unco-operative pre-filter was full of the most awful tarry substance.  So we appear to have the bug.  I sloshed in 200ml of Marine 16 Diesel Bug Treatment (for about 180 litres of diesel) but have also decided to install a Marine 16 Diesel Dipper. I will need space above the level of the diesel in order to catch the swarf and the disc of aluminium when I cut a hole in the tank for the suction pipe, so I will be leaving the tank part-full for a couple of months and then return to the boat in January to do the job. 
I don't think things will be worse and I will probably give the diesel a second dose of Diesel Bug Treatment.
In the 13 years that we have had the boat, we have had a blocked pre-filter on three occasions: first in 2007, inside the marina in Bangor, Northern Ireland when the wind gently blew us into a vacant berth, then in 2014 when in the very narrow channel entering the marina Boat Lagoon in Phuket, Thailand and now just off the marina at Licata - three times lucky to get away with it .... and I cleaned out the tank thoroughly on the previous occasions and again in 2017 when in Trinidad and installing a replacement fuel guage sender. 
My wife, Norma, is getting very fed up with this as it takes her ages to clean up her electric toothbrush after I have used it in the nooks and crannies of the tank ...

Hi Phillip,
Tell Norma I feel her pain and hope it is the last time.
I think a fuel polishing system is a good idea for any widely wandering cruising vessel and a great idea if you are in areas where one is getting fuel from 50g drums and the like. There is a secondary reason to have clean fuel besides engine performance: your fuel tanks will last a lot longer.
A dual Racor fuel filter system is also wise. Did you happen to notice the vacuum gauge reading when drawing from the clogged filter? Do you check the pressure guage regularly and was it creeping up or catastrophically rose? I would have expected some rough engine running before actually stalling: was that the case or was the stalling abrupt? Usually, (I think), there is sufficient evidence that something is awry that you can switch to the good filter before the engine becomes fuel starved and you are looking at bleeding the engine.
I took a quick look at the Marine 16 Diesel Dipper and I was left with a few questions unanswered and perhaps my quick look missed the answers: I found no track record and do not know when introduced and how many were out there. For “mission critical” systems I do not like doing the R&D for the product and would lean towards 10 years of the product being out there doing its thing and there being a sufficient amount of field reports.
I also wonder at 40-micron filter: that seems a bit course. I also suspect that the filter working when at sea and the fuel sloshing around is a advertising ploy. Any time the tanks are sloshed around the water/sludge/gunk will come loose and settle to the bottom of the tank when at rest. Any system that has access to the bottom of the tank (or at least below the pick-up tube) will then be able to get the bad stuff out when at anchor or at a marina.
Also, it is wise to have two tanks on a voyaging vessel and I suspect that would mean 2 installations of the Dipper with its attendant expense and installation issues.
If you can get to the bottom of your tank, the below might be of interest. It is Alchemy’s fuel “polishing” system that has kept our tanks clean for 70,000+ miles and lots of fuel from questionable sources.
My best, Dick Stevenson, s/v Alchemy

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 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 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.




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