ABSTRACT
The mechanism of getting a steady-state (equilibrium) condition of a tug performing escort towing in the whole range of speed is discussed. This is based on a simple but powerful analytical model. Both indirect and direct mode are investigated. Untypically, polar plots of the towing force envelope are finally computed separately for each of them, revealing some interesting specific features. Thus the user (tug designer or master) can have at hand their individual contributions to the overall performance. It is found that both modes are surprisingly important in the escort and complement each other very well. Moreover, the indirect mode, at least in steady-state, may lose its effectiveness at moderate to low speeds in that it goes with pull much below the bollard pull. A rapid transition to the direct mode can solve this operating problem.
