Trim and Draught Optimisation

Every fleet circular that has ever carried the words fuel efficiency carries this sentence somewhere: trim optimisation saves two to four per cent, it costs nothing, do it. Then, in the same week, somebody sends you a study reporting fifteen per cent, a class-society sea trial reporting nine, and an IMO page reporting half of one. Thirty to one, between figures that are all published and all honest. Nobody on that list is lying. They are answering different questions, and until you can tell those questions apart you cannot put a trim programme in a budget.

So the course opens by asking what a quoted saving is a percentage of, and works the screening sum that says, out of a ship's own draught history and for nothing, whether she is a candidate at all. It then takes the mechanism apart, because a rotation at constant displacement barely touches the wetted surface and the prize lives in the residual resistance coefficient and the propulsive factors instead. Three numbers wear the name trim, and lesson 3 pins down which is which: the static figure on the loading computer, the running attitude the water actually sees, and the value typed into a noon report once a day. The table itself is next, first for where it came from, whether tank tests, CFD or a regression on the ship's own logs, and what each route quietly froze to save money; then for its grid, read as a validity envelope in which interpolation is arithmetic, extrapolation is fiction, and the honest answer to a condition off the grid is silence. Lesson 6 sets a claimed three per cent against the noise floor of in-service measurement and asks what evidence could settle it. Lesson 7 prices what the table assumes away, since a real ship reaches the recommended trim by pumping: the ballast it takes, the displacement penalty, the cargo forgone on a deadweight-limited leg, and the visibility, strength and propeller-immersion limits that decide whether the trim is reachable at all. The last lesson turns the same arithmetic on the bigger sibling, draught and displacement, where the lever is roughly twenty times larger and nobody calls it an efficiency measure, and ends on the one-page trim policy that is this course's real deliverable.

Three required exercises run on one Excel workbook, the trim table optimiser, which looks a condition up in a four-draught table, refuses the conditions it cannot answer, weights the savings across a year's operating profile, and prices the ballast and the cargo the optimum costs. Four subjects are deliberately not taught here, and each is named where it belongs: our course Ship Resistance Fundamentals owns the calm-water decomposition and the bulb, Shallow-Water Effects owns squat and therefore dynamic trim, Proving a Device Works owns the evidence hierarchy this course points at a trim table, and our ISO 19030 course owns the filter chain and the noise floor every saving is measured against.

The opening lesson is free to read as a sample. By the end you should be able to take a trim table you did not build, say what it is entitled to answer, price the trim it recommends net of the ballast and the cargo it costs, and write the page that lets the next analyst run the ship's trim policy after you have gone.