In the Indirect mode, the aft thruster is used to orientate the tug, the assisting force is produced by respectively the hydrodynamic side force of the tugs hull and thrust forces of the forward thrusters. At yaw angles up to 45°, the tug side slips through the water and the tug’s hull acts as a rudder and is therefore able to generate towline forces in excess of the tug’s rated bollard pull. The two forward thrusters are pulling on the towline. Towline forces can be in excess of 130% of a tugboats bollard pull due to the hydrodynamic forces on the hull. When reducing thrust a Rotortug® will always return to a safe position.
This is a special way of escorting, only possible with a Rotortug®. Thrusters are close to perpendicular to the water flow and the same phenomena as in transverse arrest adds to the hydrodynamic force of the hull. Thrusters are used to orientate the tug as well as for generating towline forces whereby additional towline forces are produced by the hydrodynamic side force of the tug’s hull. The heeling angle is limited to approx 8 degrees.