Highligts Issue 4: May 2002

Bunkers - Cheap is not always Best

Fuelling a ship is an expensive business. So expensive, that it funds an industry in itself "The Bunker Business." Operators, both owners and charterers, have to look to their margins and minimising fuel costs is an obvious factor. However, this is an area where cheap is not always best is particularly relevant.

Historically, marine fuels were produced as distillate products in refineries. The specification and quality of a distilled fuel is very consistent and the end product is both homogeneous and consistent in quality. However, distillate fuels are history. Today, marine fuels are almost universally blends. The feedstock that goes into the blend is very varied and has produced, over the years many combustion problems.

Those problems are usually associated with the incompatibility of the fuel feed stocks. The problem may manifest itself within a particular bunker supply, or may materialise as the result of mixing of bunkers from different stems on a ship.

The problem has been sufficiently endemic to cause the UK FD&D Club to issue circulars warning of the problems, recommending members to join one of the fuel quality testing programmes (see circulars dated December 1981 and October 1990). The usual cause of combustion problems is the precipitation of catalytic metal fine elements in the fuel. This is produced as a result of incompatibility between the feedstocks in the fuel, or incompatibility between different bunker fuels in a ship's tanks.

The catalytic fines are metal elements, normally aluminium, vanadium or silicon, and these fines when burned in the ship's engine produce excessive exhaust temperatures which can cause serious, and expensive problems with the marine engines. The engines may also suffer physically from abrasive mechanical damage.

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