The Triton


Meticulous captain, engineer can face diesel issues onboard


Nigel Calder, the dean of do-it-yourself yacht maintenance, in his “Boatowner’s Mechanical and Electrical Manual” puts it very succinctly: “It is … of vital importance to be absolutely fanatical about keeping the fuel clean.Yet so many boat owners treat their fuel system with indifference. … The result is that 90 percent of diesel engine problems result from contaminated fuel.”

And he is right.

Many captains and engineers, no matter what the length overall of the yacht they work on, are meticulous about changing the oil, oil filters and fuel filters on their diesel engines and generators.

However, they give little thought to the diesel fuel itself, the lifeblood of those engines and generators.

Just about every crew member has a story of a diesel engine conking out at the most inopportune time. In heavy seas, the primary Racor filters can clog up as the contaminants at the bottom of the fuel tank are stirred up then sucked up into the fuel system’s pickup tube.

There is a better way. Start a preventive maintenance program for the diesel fuel on your yacht.

Filter-clogging tendencies depend on factors such as transportation from the refinery and storage, natural oxidation and breakdown, the source of the crude oil, use of production additives and the addition of biofuel.

In the past decade, due to oil supply and environmental concerns, changes in fuel production related to cracking, blending and lower sulfur levels have added to the instability of diesel fuel and shortened its shelf life.

Today’s common rail diesel engines have injection systems that operate with pressures of 30,000 psi or greater. These injection systems require that the particle size of fuel does not exceed the engine tolerances. Inorganic contaminants such as sand and rust can be easily filtered out and removed.

However, standard fuel line filtration systems have no affect on the natural tendency for diesel fuel to agglomerate and form organic contaminants that clog the filters.

Diesel is a complex fluid. It is not homogeneous, and no two batches are identical. Fuel deterioration and shelf life depend on a variety of factors including good housekeeping. Fuel breakdown is also dramatically accelerated by changes in temperature, water, microbial growth and exposure to heat and pressure from engine injection systems.

In the diesel fuel industry, terms such as algae, gum, wax, resin, varnish, tar and asphaltenes are used to describe the organic gunk that clogs filters. This gunk caused by fuel degradation is an inevitable, natural process. And unless adequate fuel sampling, testing, monitoring and maintenance is performed, fuel breakdown will continue.

Some captains believe that they cannot have fuel problems because their yacht is not a dock queen and the fuel in the tank is burned through regularly. The fallacy in this belief is that most of the contaminated fuel in the tank sits at the bottom. The fuel pickup tube in the tank can be located as much as six inches above the bottom of the tank. Those six inches contain water, anaerobic bacteria, mold, asphaltenes and other compounds. This last dirty bit of fuel is never used, and is the exact purpose of having the pickup tube located above the tank bottom.

But once new clean fuel is bunkered and introduced into the dirty fuel at the tank bottom, the new fuel also gets contaminated.

Eventually, the level of the contaminants builds up to a height high enough to enter the pickup tube and start clogging the filters, which results in poor engine performance or engine shutdown.

A simple analogy is discovering a gallon of milk in the back of the refrigerator that has been sitting there for a few weeks with just a pint left in the jug. You’ll have sour milk. But add three quarts of fresh milk to that sour milk and within a short time, all that new milk will turn sour, too, as bacteria spread throughout the milk.

A diesel fuel preventive maintenance program is what you need to keep the fuel clean and reliable. Done right, your yacht will arrive at that hidden anchorage just before sunset and every guest will have ice cubes in their cocktail at happy hour, and no one will be the wiser.


Capt. Jeff Werner has been in yachting more than 20 years on private and charter yachts, both sail and power. He is an instructor for RYA, MCA, USCG and US Sailing courses and owns Diesel Doctor ( Comments on this column are welcome at

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