Stay Signed In
Do you want to access your site more quickly on this computer? Check this box, and your username and password will be remembered for two weeks. Click logout to turn this off.
Stay Safe
Do not check this box if you are using a public computer. You don't want anyone seeing your personal info or messing with your site.
These are the notes and slides used by Paul on Ballena for a presentation at the 'Skippers De-Stress Forum'.
Some notes using references supplied ( )
Quote from Easymoor (1) ´There are two types of boat owners – those who have had a breakdown at sea due to fuel contamination, and those who haven´t –yet’
1. We choose a diesel engine at sea because it does not need a spark! Just fuel and air. Clean air is easy to provide (except in a sandstorm) but why do we assume that we will always be able to supply clean fuel, just because we have fitted new filters at the beginning of the season?
2. How often do we look into our fuel tanks? Why should we have to bother when we have the very best of fuel/water separators? Anyway we all filter our diesel before it goes into the tank!
3. So we are not going to have an engine failure at sea due to fuel contamination because, although we do not really need it, we have always added an anti-bacterial treatment (when we remember!!!).
4. So what is it (in other peoples tanks) that causes a problem? Diesel Bug (slide 1 (2)) We can see a growth at the water/fuel interface- the ideal place for Cladisporium Resinae to grow. This one of about 27 varieties of fungal or bacterial contaminants that can occur in diesel fuel. (3)
5. If this bug, or similar, gets a grip on the tank ‘then filters will start blocking with a black slimy deposit and the fuel will be hazy with water and dirt suspended in it’ (4) (slide 2). At the bottom of the fuel there can be a layer of sludge and dirt that does not cause a problem until it is high enough so that agitation of the tank in a bumpy sea causes the level to come above the intake level.
6. So what are the conditions that encourage the onset of diesel bug problems? Essentially a combination of water and diesel, and warmth will provide the ideal conditions for growth. BUT where did this thing come from in the first place.
7. Diesel bug is delivered to your door in various degrees of contamination by the suppliers from shore tanks, road tankers, even the local garage and we are very prudent with our fuel. We like to keep it as long as we can and not use it unless it is absolutely necessary!! (the bugs might have well hung out a sign saying ‘do not disturb, breeding in progress!!)
8. How does the water get into our tanks? Diesel is hygroscopic (absorbs water from the air)(5) which means you cannot avoid it, and the tank breather is always open for obvious reasons. Tanks left partially full attract condensation on the tank walls and roof. Poorly sealed deck filler caps let the water in (and a bit of salt!)
9. The diesel bug lives in water breathing air (aerobic bacteria) (slide 3) and eating hydrocarbon products in the diesel. When all the air is used up their cousins (anaerobic bacteria) take over. Evidence of anaerobic bateria is a brown sludge sometimes sticking to the tank walls or growing in the corners. (slide 4) These are sometimes referred to as Sulphate Reducing Bacterias (SRBs) also Iron Reducing Bacteria (IRBs)
10. The by products of these bacteria are the familiar black slime (slides 5 and 6) and sulphurous compounds. The suphurous compounds can combine with the water to form sulphuric acid, As this passes through the pressure pump and injectors there will be corrosion! Meanwhile the black slime can grow to a significant volume and block fuel pipes as well as filters. (slide 7)
11. Testing kits are available if you want to test the new fuel supplied for fungal or bacterial contamination. These are culture kits and require 24 hours or more! Try keeping a tanker waiting for 24 hours!!!! You can take a sample and put in a bottle containing a little water and put somewhere warm to see if something happens. If it does then it is in your tank.
12. The other contaminants come from the refinery! These are the asphaltenes which are by-products of the refining process. (6) These can come out of suspension by ageing (coagulation) or by mixing fuels from different sources. If one fuel has been under-treated and is mixed with an over-treated fuel then further coagulation can occur. The result in both cases is a brown/black sludge often called waxing. (slide 8)
13. Low Temperature can also cause a problem if there is a high asphaltene content. This is when ‘waxing’ can occur and form blockages in fuel lines. (7) The tank temperature is affected by the air temperature unless it is built into the hull then it will more likely take on the water temperature (which can be an advantage)
14. What can we do to keep reasonably safe? No matter how we store the fuel, and for how long, our goal is to ensure that clean fuel enters the injector pump. At the moment most boats rely on a water separator (independent of the engine) and a final filter attached to the engine. Of course if the contamination of the tank is severe then you may have to resort to ‘fuel polishing’ which effectively means cycling the fuel through fine filters until it is clear. However it often means that this is simply returned to a dirty tank, since cleaning a fuel tank is such an awful job!! (slide 9)
15. The commonest method for containing the Diesel Bug problem is to add biocide to the tank both as a first strong dose as recommended and later as a regular dose each time you top up the tanks. Also by ensuring that the tanks are always full, especially during long periods of rest, will help to reduce condensation. There are many products on the market to combat the Diesel Bug. These BIOCIDES claim many different properties and you have to decide which one is the best. Although they seem expensive, the price off a single dosage is quite low, so the bottle will last a long time.
16. However it may be worthwhile to look at your fuel system to see if there any preventative measures to reduce the likelihood of contaminants reaching your engine. Preventive measures may include one or more of the following:-
a) fitting double/bypass filtering
b) installing a day tank
c) fitting ‘kidney loop’ filtering
d) tank sump drain off
e) sump riser pipe
f) inspection cover/window
g) double tanks and manifold
A. Double bypass filtering: Two water separator filters set up in parallel and isolated from each other so that if one blocks at an awkward time it may be possible to use the other one until the cause is solved. This may also avoid priming before having to restart the engine!
B. Installing a day tank: A 30 to 100 litre tank situated preferably above the high pressure pump level. It should be fed by a small (but adequate) electric (vehicle) fuel pump with auto-level or manual switching, and with a manual pump override. The fuel can be drawn through a water separator and fine filter.
C. Kidney loop filtering: Using a second take off and return line for the fuel tank and fitting a filtering system and pump (vehicle) in the line. This can be run regularly, when the engine is on, to act as a self polishing system. The take off inlet for the kidney loopshould be lower than the engine intake inlet.
D. Tank sump drain off: If your tank has not got one it is likely that it is not possible anyway. Ideally there should be a drain off point directly under the engine take off pipe. (It is standard practice for aircraft to check the fuel drain off for water before every take off.)
E. Sump riser pipe: If the tank is low in the boat or there cannot be access to the lowest point of the tank then it may be possible to fit a sump riser pipe through the top of the tank. This can be normally capped off but opened and a suction device attached to draw fuel/sludge from the lowest point in the tank at service intervals.
F. Inspection cover/window: The main problem is that we do not know what is in the tank until trouble occurs. An easily accessible inspection cover (maybe with a window) will at least give you the possibility of an early warning and a chance regular maintenance.
G. Double tanks and manifold: If there is an opportunity to increase your range by installing a second fuel tank that can be connected with a common manifold with drains and maybe dual filtering. The return line must also go to the manifold; this also reduces the build up of temperature in the tanks due to return line fuel.
(Copy and paste the address into your web browser)
Compiled by Paul ‚BallenaGanova’ , Marmaris Yacht Marina, Dezember 2008
Appendix: After coming across this problem in one or two tanks I developed a system for de-sludging diesel tanks without having to remove all the fuel. Experience with over 20 tanks has shown those most likely to have a potential problem is ALL tanks. Having said that some tanks were definately cleaner than others and the worst culprits seemed to be steel tanks.
Depite every effort by the owners to keep the tanks full I have found water in most tanks, over two litres in one case. Diesel bug in various states has appeared in nearly all tanks but biocide treatment had kept it under control.
In nearly all cases access to the tank was limited and in several cases nigh impossible, and with a very limited ability to inspect or clean. In several cases, after we have desluged the the tank, the owner has gone on to provide better access for the future, or at least put it on the todo list.
If you would like further details on desluging please contact Paul on Ballena-Ganova YM
