FORCE ON THE MOORING LINES OF A SHIP DUE TO THE HYDRODYNAMIC INTERACTION EFFECTS OF A PASSING SHIP

The hydrodynamic interaction forces acting on a moored ship due to the passage of another ship is estimated using slender body assumptions. The computations are performed for an assumed parabolic sectional area distribution for the ship and also using the real ship form. Subsequently the equations of motion of the moored ship are solved to study the forces on the mooring ropes for different rope constants. The obtained hydrodynamic interaction and mooring rope forces are compared with known experimental/ theoretical values. Interaction effects between ships arise from changes in the pressure fields surrounding the ships. These effects become more significant when they operate in proximity to each other, such as when operating in a harbour, a channel, a canal, fair way or in other confined waters. The hydrodynamic interaction forces, which are amplified in close encounters in restricted waters, should be properly understood to assess the eventuality on a vessel’s mooring lines and to avoid the probable risk of collision. There are incidents where a ship moored in a quay starts moving by breaking the mooring lines and also a lot of cases of collision with a passing ship due to the hydrodynamic interaction between them. Since there is a phase lag between the mooring rig failure and the interaction forces and moment, the effect may be noticed only after the passing vessel has moved away. So, it is evident that passing ship effects can be disastrously high to a moored ship unless it is properly moored. So another important area where proper attention is required due to the hydrodynamic interactive effects is the design of mooring and fender systems.