Entry & progression
Management level means understanding where the energy goes. A watchkeeper reads the gauges. A chief knows what the numbers mean, what they should be, and what it costs when they drift.
Every litre of fuel you burn is a quantity of chemical energy. A marine diesel converts a substantial fraction of it into shaft work - large low-speed engines do best, high-speed engines rather less - and everything else leaves as heat: out through the exhaust, the jacket cooling water, the charge air cooler, the lubricating oil and radiation from the block. That is not waste in a moral sense. It is the second law, and no amount of maintenance repeals it.
The heat balance
The chief's use of a heat balance is diagnostic. If exhaust temperature after the turbine is rising at constant load, energy that should have been doing work is leaving as heat: fouled turbocharger, dirty air cooler, worn injectors, poor combustion. If the jacket water heat load climbs, so has the heat rejected into the liner. Every quantity of energy has to end up somewhere, and finding out where is how faults get diagnosed before they become failures.
Specific fuel oil consumption
SFOC - fuel mass per unit of work, typically grams per kilowatt-hour - is the honest measure of engine efficiency. Two cautions. First, it is only comparable when corrected to reference conditions: ambient temperature, charge air temperature and barometric pressure all move it. Second, it depends on the lower calorific value of the fuel actually in the tank, which varies bunker to bunker. Trending an uncorrected SFOC across two fuel deliveries tells you about the fuel, not the engine.
TIP — On a yacht, the hotel load is not a rounding error Air conditioning, galley, laundry, stabilisers at anchor, tenders, water makers and very large AV loads mean the electrical demand of a big yacht at anchor can rival anything the merchant world would expect for the hull size. Meter it. You cannot manage a consumer you have not measured, and the biggest saving on most yachts is not in the main engines at all.
Where the money actually goes
- Hull and propeller fouling. Roughness costs power; power costs fuel. A fouled propeller is one of the most expensive and least visible faults on any vessel.
- Trim and displacement. Out-of-trim vessels burn more. So do vessels carrying full tanks they do not need.
- Speed. Resistance rises steeply with speed, and the last couple of knots are grotesquely expensive. It is usually the master's most powerful fuel lever.
- Machinery loading. Generators run lightly loaded are inefficient and, over time, damage themselves. Load them properly or shut one down.
- Waste heat recovery. Exhaust gas economisers turn rejected heat into steam or hot water. They also collect soot - and soot in an economiser burns.
Fuel and emissions
Every tonne of fuel burned is a fixed quantity of carbon dioxide out of the funnel - you cannot filter your way out of it, only burn less. Sulphur oxides track the sulphur in the fuel. Nitrogen oxides track combustion temperature and pressure, which is why chasing peak efficiency and chasing low NOx pull against one another. MARPOL Annex VI governs air emissions internationally; which limits apply to a given vessel in a given sea area is a flag and class question.
CAUTION — Emission limits are not in scope of this course Applicable emission control areas, fuel sulphur limits and reporting obligations depend on the vessel, the flag and the area. Confirm them with the flag administration, class and AMSA. Do not run a bunkering plan off a training module.