Steady-state Manoeuvring of a Generic ASD Tug in Escort Pull and Bow-rope Aided Push Operation

This paper is devoted to expand the very promising research undertaken in the author's previous work, basically done on simplified modelling the escort push operation. Now, the other two modes of a tug's employment, as stated in the title, are covered. The special focus is again set on the indirect towing in that the towline force is much higher than the thruster force. The ratio of these two forces, referred to as the relative towing force (or amplification ratio) is evaluated together with the hull drift angle and the thruster(-s) angle for a given escort speed. This mutual relationship is known as the tug performance diagram. Although rather generic (container-type) formulas are derived, they are supplied for exemplification purposes with simple, analytically given hull hydrodynamic forces. The aim is also here to provide a basis for further sensitivity analysis of the model and possible improvement/optimisation to the tug design. The obtained charts also could serve as rough and clear guidance for towmasters while escorting.