Voyage optimisation is software that plans each voyage's route and speed, so that a ship arrives on time while burning as little fuel as possible, and that measures the fuel burned and the emissions produced on the way. It is also called voyage planning or weather routing.
Fuel is the largest running cost of most ships. A ship's fuel use rises very steeply with its speed, so going a little slower saves a lot of fuel. Weather matters too. Strong headwinds, high waves and currents against the ship make it burn more fuel for the same distance. So the software combines three things: the ship's own record of fuel use at each speed, the weather and ocean forecasts for the coming days, and the time at which the ship must arrive.
Imagine a bulk carrier bringing 75,000 tonnes of coal from Indonesia to Paradip port in Odisha, a trip of about 2,700 nautical miles. At 14 knots, it would burn about 30 tonnes of fuel a day and arrive in 8 days, using about 240 tonnes. A knot is a speed of one nautical mile an hour. But the port has said that its berth will be free only in 9.5 days. Arriving early would only mean waiting at anchor. So the software suggests 12 knots. At that speed, the ship burns about 19 tonnes a day and arrives just in time, using about 180 tonnes. It saves about 60 tonnes of fuel. Burning one tonne of ship fuel releases about three tonnes of carbon dioxide, so the ship also releases about 190 tonnes less. The software also moves the route south, away from a storm forecast in the Bay of Bengal.
Measuring matters as much as planning. Since 2023, the International Maritime Organization, the United Nations body for shipping, rates each large ship every year by its carbon intensity: the carbon dioxide it releases for each tonne of cargo carried over each mile. A ship with a poor rating must present a plan to improve it. So the software records the fuel burned on every voyage and calculates the rating. It sends these numbers to the shipowner's carbon accounting software. There, they count among the owner's Scope 1 emissions, the emissions that a company releases directly.
The voyage plan is useful to others too. Ship management software uses it to deliver supplies at the right port. Supply chain visibility software uses the expected arrival time to tell the cargo owner when the goods will reach port. Voyage optimisation is one of the ship's tools described under ocean freight and customs.