A fuel system causes trouble in two ways: by stopping the engine, or by creating a fire risk. The first happens at sea at the worst moment; the second even in port. The survey follows the line from deck fill to injectors.
From deck to engine
- Fill and vent
- Fill cap seal and bonding; a vent outlet raised so it cannot take on water.
- Tank
- Mounting, weeping, inspection hatch, and water or sediment at the bottom.
- Shut-off valve
- At the tank outlet, reachable from outside the engine room; this is how fuel is cut in a fire.
- Hoses
- Fire-resistant fuel hose (ISO 7840) with proper clamps; hardening and cracks.
- Filter and water separator
- Water and sediment in the bowl; filter change date.
- Return line
- The line carrying fuel back from engine to tank; leaks and connections.
Fuel quality
On a boat left standing for long, water and microbial sludge form at the tank bottom; filters block often and the engine falters under load. A sample from the tank bottom and the filter bowl are the first clues. Cleaning is done by opening the tank or by fuel polishing.
What we often see
- Hardened, cracked fuel hoses: Fuel hoses hard with fine cracks on the outside; manufacture date unreadable.
Continue with this topic
- Fuel planning: Consumption and reserve.
Before going to sea
Most fuel system trouble comes on the first passage of a boat that has stood for long. Water and sediment at the tank bottom are stirred up in a sea, reach the filters, and the engine falters just when it is most needed. So after a long lay-up, the water separator bowl is checked and drained before the first passage, and a spare filter is kept ready. Knowing how to bleed the system after a filter change is how a small problem at sea is solved before it grows.
What happens at the tank bottom
At the surface where diesel meets the tank, especially if there is water, micro-organisms can multiply. The result is a dark, jelly-like sludge on the tank bottom and in the filters. Signs are frequent filter blockage, loss of power under load and dark sediment in the filter bowl. Prevention is keeping water out, not leaving the tank half-full for long periods, and sampling from the bottom regularly. When cleaning is needed, the tank is opened or the fuel is polished by circulating it through a filtration rig.
Deck fill and vent
When the fill cap seal wears, rain and spray go straight into the tank. The vent outlet must be raised and looped so it cannot take water in a sea. A blocked vent can cause overflow while filling or a pressure difference inside the tank.
When refuelling
Engines and any open-flame appliances are switched off while refuelling, and spills are cleaned before they reach the water. On petrol boats, the engine compartment is ventilated after refuelling and before starting.
A consumption log
Recording every refuelling with engine hours reveals the boat's true consumption over time. An unexplained rise in consumption can be the first sign of a fuel leak, a foul bottom or an engine problem. The same log is the most reliable basis for planning a delivery's fuel.
Fuel problems rarely have a single cause; water, sediment, worn hose and a dirty filter act together. So the survey reads the system as a whole, from deck to injectors.