Dirty diesel is the offshore sailor’s most insidious mechanical problem. Not insidious because it is complicated, the diagnosis of a fuel contamination issue is usually straightforward once the symptoms appear. Insidious because the contamination that grounds the boat in the anchorage or stops the engine in the channel or fouls the injectors on the third day of the Atlantic crossing entered the fuel system silently, at the fuel dock, in the form of the diesel that looked and smelled correct and that was anything but.
Diesel contamination takes two primary forms. The first is water contamination, water that enters the fuel through condensation in the partially full tank, through a faulty deck fill cap that allows rainwater or sea spray to enter, through the fuel dock’s own delivery system whose tank has not been managed correctly. Water in diesel does not immediately stop the engine. It accumulates in the bottom of the fuel tank, where the Pseudomonas and Hormoconis resinae bacteria that live at the water-diesel interface metabolise the hydrocarbons and produce the black sludge that is the second form of the contamination and the form that does stop the engine.
The diesel bug blocks the primary fuel filter, the secondary filter, and eventually the injector if the blockage is not caught at the filter stage. On the offshore passage three hundred miles from the nearest port, the blocked injector is the emergency. The dirty diesel at the fuel dock two weeks earlier was the cause.
Where the Contamination Comes From
The fuel dock is the most common contamination source. The marina fuel tank that serves the charter fleet in the summer season and the delivery vessels and the commercial fishing boats and the occasional offshore passage maker receives fuel deliveries at irregular intervals and has a turnover rate that varies significantly between the high-season marina with the constant demand and the off-season or low-traffic facility where the same diesel has been sitting in the tank for months.
The diesel that has been sitting in a shore-based tank for several months in a warm climate has had the time for the condensation cycle to introduce water and for the bacterial growth to begin. The marina fuel dock with the slow turnover is the fuel dock whose diesel may already contain the contamination before it enters the boat’s tank.
The remote fuel dock compounds the problem. The Indonesian fishing village that sells diesel from the drum on the jetty, the Pacific island that receives fuel by inter-island supply vessel once a month, the Red Sea port where the fuel quality control infrastructure of the European marina does not apply, these are the fuel sources that the offshore circumnavigation uses when the route is in the part of the world where the certified marina fuel dock is not the available option.
The drum on the jetty is the drum that the local fisherman uses, that was filled from the delivery vessel that filled it from the shore tank that was filled from the supply chain that may or may not have maintained the cold chain and the water separation that the high-quality diesel supply requires.
The Naora circumnavigation passes through forty countries over five years. The fuel quality varies across this range from the certified high-turnover marina diesel of the Mediterranean and the Caribbean to the drum-on-the-jetty diesel of the remote Pacific island and the Indonesian fishing village.
The fuel management system on the Eighty2 was designed to handle both ends of this range and everything in between, not by avoiding the low-quality fuel source when it is the only available option, but by treating every fuel source as the potential contamination risk and applying the filtration and separation system that converts the contaminated fuel into the clean fuel the engines require before it reaches the injectors.
