Bunker

The word bunker comes from the compartments, or bunkers, where steamships once stored the coal that fired their boilers. Although ships long ago switched from coal to oil, the language stayed: a ship's fuel is its bunkers, the act of loading fuel is bunkering, and the note recording a delivery is the bunker delivery note. Bunker fuel is distinct from cargo; it is what the ship consumes to move itself and generate electrical power, not what it carries for a customer.

Marine fuels come in several grades. Heavy fuel oil, a thick residual fuel that must be heated before it can be pumped and burned, has traditionally been the cheapest and most widely used on large ships. Distillate fuels such as marine gas oil and marine diesel oil are lighter, cleaner-burning and more expensive, and are used in port, in emission control areas and by smaller vessels. Since the IMO 2020 rule capped sulphur content at 0.5 percent outside scrubber-fitted ships, very low sulphur fuel oil has become the mainstream grade, and alternative fuels such as LNG, methanol and ammonia are entering service as the industry works to cut carbon emissions.

Bunkering is a carefully controlled operation because a fuel spill is both an environmental offence and a fire hazard. Fuel is usually delivered by a bunker barge alongside or from a shore installation, following an agreed plan, a signed checklist and continuous monitoring of tank levels. Representative samples are drawn and sealed at the point of delivery so that any later dispute over fuel quantity or quality can be resolved. Because fuel is one of the largest costs in running a ship, bunker prices, fuel consumption and bunkering ports are central to how voyages are planned and vessels are operated.