The Other Engines: Diesel Generators and the Electrical Load

Ask where a ship's fuel goes and you will be told about one engine. The other two or three burn up to 15% of it, on IMO's own reckoning, and on a tanker with electric cargo pumps more than that; few offices see the number as a line of its own, and the chief runs a second set on passage because that is what a careful chief does. Nobody has priced it. On the ship this course works throughout, the habitual second set at sea costs about 57.5 tonnes and 31,600 USD a year, and stopping it buys no hardware at all: it is a standing order, a setting in the power management system and someone in the office who reads the running hours.

This course is the fuel-and-decision side of the electrical plant, taught for the people who manage it. It runs in the order the decisions do: the auxiliary tonnes sized from published tables and the DCS consumer split, and placed beside the main engine's, so the ship that deserves a file is named before anyone spends anything; the generator's fuel curve read from two makers' project guides, flat from 75% load upward and steep below 50%, turned into kilograms an hour and tonnes a year; the count, one set or two or three on the same demand, with SOLAS read for what reserve actually means; the split between sets forced to run together, where the PMS's equal share is a stability convenience rather than a fuel optimum; the load balance rebuilt as measured averages by mode, and the switchboard meters that turn it from a yard drawing into a live signal; the shaft generator, priced at the extra fuel the main engine burns to carry it at the load actually sailed, against a genset run properly rather than the plant as found; the port stay, the worst hours the plant runs, with a plan per port and shore power as the limiting case. It closes with the energy audit as a procedure that ranks all of that in tonnes for one ship, written into SEEMP Part I as triggers with owners and numbers, and the company-level indicators that keep them alive after the next crew change.

Three things it deliberately does not teach. Why a four-stroke's fuel curve is a valley, the PTO and PTI architecture and the disciplines that keep the lights on when a set trips are the territory of our course Marine Engineering & Main Engines, in its lessons on specific fuel consumption, on batteries and hybrid power and on operating for reliability; the shaft generator's hardware, the hotel consumers and the shore-power connection itself belong to our free course Energy-Saving Technologies; and the boiler's fuel, which this course leaves out of its share on purpose, is our course Auxiliary Boilers and Steam (available shortly). What this course adds is the arithmetic between them, and it carries a workbook for it: the generator loading calculator, an Excel sheet for enrolled learners that takes a maker's curve, a three-column load balance and the count the crew actually runs, and returns the fuel of one, two and three sets, the price of the habit, equal against asymmetric sharing, and the shaft generator's saving, break-even and payback.

The opening lesson is free to read as a sample. By the end, you should be able to put the auxiliary tonnes on the same page as the main engine's for every ship in the fleet, say which of them has a generator problem and how large it is, write the standing order and the PMS table that fix the cheap part of it, and judge a shaft-generator, harbour-set or shore-power proposal against a plant that is already being run well, which is the comparison the brochure never makes.