Water is a component of petrol, so it comes on board and into the tank when refuelling. The amount is around 100 mg/kg for fresh fuel, and this value increases over time. One reason for this is the humidity or direct water supply. The latter is more common at foreign boat refuelling stations.
Low throughput rates and large tanks favour the separation of water and fuel, as do enormous temperature fluctuations. The bunker station's fuelling system draws in the lower part of the tank, i.e. where the water is located after separation. As the pump cannot distinguish between petrol and water, it also pumps the water into the fuel tank of the pleasure craft.
BOATING TIP: Before refuelling at bunker stations, you should get information about the station in a nearby harbour if possible. This may save you a lot of trouble. If you want to be on the safe side, you should get your petrol from the car filling station in canisters. The higher throughput rate and the underground tanks reduce the risk of getting fuel "contaminated" with water.
Another possibility for the water content in the petrol to increase is the formation of condensation on the inside walls of the tank. This then runs down and dissolves in the petrol. You can prevent this by always filling your boat's tank as full as possible, thus reducing the surfaces on which condensation can form. Insulating the fuel tank on board - which is also conceivable - is often very costly and not always completely feasible, but it is also a very effective measure to prevent condensation permanently and sustainably.
The filler cap and tank vents are also two openings through which a lot of water can easily get into the tank. The "classics" here are defective sealing rings on the filler necks, coupled with an unfavourable installation position, for example flat on the side aisle. With this installation, the water from the foredeck and the superstructure runs over it. In addition, the filler neck installed in this way stands in the water when it rains and cannot prevent it from entering if the seal is damaged.
The situation is similar with the ventilation openings for the tank. These should be positioned so that neither rain nor spray water can run into them. BOOTE tip: Check the seals and the general condition of the tank nozzle every time you refuel. This is because damage to the sealing surface and the cap, as well as broken seals, can be responsible for "water ingress" in the fuel tank.
Once all conceivable sources of water ingress have been sealed and checked as far as possible, the second step is to protect the engine or fuel system from water with a further measure. This is a filter system with a water separator that is customised to the respective engine. This is important to ensure that both the filter and the water separator function properly.
If the system is too small, it will not be able to separate all the fuel from the water. This results in frequent emptying of the water separator - as well as a drop in engine performance. If the filter with separator is too large, there will be problems with the filter performance, as the filters require a certain flow rate in order to optimise the "water insulation". Suitable filters with water separators and drain plugs as well as sight glasses are available for many engines directly from the engine manufacturer or from maritime accessory dealers.
Some skippers may be asking themselves: "Why all this, the engine is still running?" "Still" is the right way to put it. It is certain that the carburettor or the injection system as well as the engine itself are affected by water in the fuel. The reason for this is the lack of lubrication and corrosion protection, which are washed away by the water. The consequences are increased wear
as well as rust in the fuel system. Clogging or damage to the carburettor and fuel pump cannot be ruled out.
"Phase separation" describes the process in which, for example, water separates from the remaining petrol. This separation is favoured by a drop in temperature and requires an increased proportion of water in the fuel. The impending phase separation can be recognised by a visible clouding of the fuel. If the water content continues to rise, the fuel splits. Due to the higher density of the water, it sinks to the bottom of the tank. A water bottom forms - the process cannot be reversed.
One way to reduce or dissolve the water film is to bind it using chemicals such as tertiary butyl alcohol, which allows it to be burnt off. Additives such as Yachticon's condensation binder work in this way.
If there is a large amount of water in the tank, draining or pumping it out is the last option for getting it out again. Older pleasure craft have a drain plug for this purpose, which can be used to empty the "tank sump". If this is not possible, the tank must be drained via the service hatch or tank sender opening.
And where can I take the contaminated fuel? The disposal of the petrol/water mixture should be organised via the local pollutant collection point. You can find out where to do this on the Internet or by contacting the municipal waste disposal service.
