Required tug power and number of tugs needed in variable conditions of wind, current and waves isin most cases an assessment made by pilots based on their professional experience. However, assessments will raise questions by lawyers if something goes wrong. They will use tools to calculate what really is needed with respect to tug power and number of tugs. They have furthermore the advantage of time.
Research on hydrodynamic interaction indicates that if the speed of the ship near a bank is too high, the rudder may be less able to cope with the forces induced and control will be lost. The Nautical Institute highlights this in its latest Mars Report, in which an LPG carrier hit a barge being towed by a tugboat as a result of hydrodynamic forces.
