WATCH: Indirect Towage - The smart technique behind massive ships making tight turns!
Indirect towage is a method employed by tugs to achieve a high turning force on ultra large and megamax container ships calling at the Port of Felixstowe, which has an extremely tight corner at the Harbour entry, Beach End Turn.
Pilots also combine this with a second tug pushing on the ship's quarter while she is making the turn, to enhance the steering effect.
Here's a text about indirect steering:
Indirect towing is a way of enlarging the exerted force when turning and/or decelerating the tow. This mode applies only to the trailing tug, here referred to as the stern tug. The tug is made fast to the vessel by a towline and is dragged by the assisted vessel. The tug uses its thrust to maintain a
sheered position relative to the tow’s heading whilst the towing force is generated by the drag forces acting on the tug’s hull and transmitted via the towline. The drag forces on the tug can be substantially higher than the bollard pull when the speed through the water is greater than 6 knots
(approx).
With the towline at a large angle to the tug's centre line, indirect towing is a potentially dangerous manoeuvre. Indirect towing requires a highly skilled tug master to achieve the high towline forces without girting and capsizing the tug. The advent of the purpose-built escort tug, designed for exerting such high loads, has made this operation much more controllable and therefore much safer.
Text from Peel Ports