Electric power for efficient tugs

A main ship review, of a vessel described as ‘the world’s largest motor tanker’ showed that sector, at least, still had a long way to go. A 235m, 50,000 ton tanker with 22,500bhp (albeit in twin screw configuration) is pretty unremarkable now. But elsewhere in the magazine, engines of bore 840mm to 900mm were seen as the way forward, a note of despair was sounded at the high proportion of laid-up ships, and hopeful noises were being made about gas turbines. Then, they were being held back by being confused by various certification bodies with steam turbines.

With interest currently being shown in hybrid propulsion (as in diesel and battery) for harbour tugs, it’s interesting that in 1960 diesel electric plant had been chosen for new, ultra-powerful, tugs for the Suez Canal. Then, as now, justification for veering from the purely mechanical norm came from the way that electric propulsion can accommodate a wide range of power requirements without loss of efficiency. The Suez tugs had two 1600bhp V16 GM two-stroke diesels, each driving two DC generators, supplying a twin-screw system powered by four electric motors, all of which could be switched in and out in various combinations.