engineering
Allabout fuel At the core of Nordhavn’s reliable, easy-to-use fuel system is an ever-present force—gravity By James Kirby
contributing editor
The fuel system used on Nordhavn yachts is simple, reliable and easy to use. But it took a good deal of thought and work to make it that way. To understand how it works—and to appreciate what makes it better than other marine diesel fuel systems—let’s first take a look at the obstacles its designers had to overcome. Diesel engines have a reputation for robustness and durability. However, they have an Achilles heel—the injection pump and the individual fuel injectors. These precision parts are built to incredibly close tolerances, on the order of 0.0004 in., and operate at pressures between 1,500 and 5,000 psi. The presence of the tiniest amount of contamination can damage or destroy them, requiring expensive repairs. The subsequent loss of propulsion is a serious matter at the best of times, and it doesn’t take much imagination to realize what can happen at the worst of times. The culprit here is the fuel itself. According to CAV, one of the world’s largest manufacturers of fuel injection equipment, 90 percent of diesel engine problems are the result of contaminated fuel. People coming from a gasoline engine background are usually shocked to learn that diesel fuel is so troublesome. Like gasoline, diesel fuel is clean when it leaves the refinery, however it has an uncanny affinity for attracting a wide variety of contaminants.
Diesel’s dark side Water is always present, having arrived as condensation in the fuel tanks. The effects of water in diesel fuel can be serious. It can cause a tip to blow off an injector, or reduce the lubricity of the fuel, which can lead to the seizure of close tolerance assemblies. It can also corrode metal fuel tanks. Dissolved waxes in the fuel increase its energy content, but they can precipitate out at low temperatures and clog filters. For this reason, fuels are blended for specific climates. Trouble occurs when a vessel takes on a load of fuel blended for a warm climate and then travels to a cooler climate. Tar-like substances called asphaltines can also form and settle out of the fuel over time, only to become suspended again and clog filters when heavy seas agitate the fuel. Diesel fuel can also be contaminated by solids such as silt, sand or ash, which it acquires while being transported, or from storage in dirty tanks on shore or on the boat. These hard particles are particularly destructive to precision pump and injector parts. How clean is the fuel in that tank truck? A system that can eliminate contamination is essential for any boat, but especially a long-range yacht.
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