Question
Is it necessary that stiff or soft fenders be designed for berthing in piers?
Answer
Elasticity of fenders is related to ability to release stored energy during berthing of vessels. But, it does not make any effect on reaction force and deflection of fender system. Quantity of energy that fender can absorb is dependent on reaction-deflection curve and is represented by area under the curve. Higher is reaction force, higher amount of energy will be absorbed by a fender provided that resistance of ships' hull is enough to withstand the force without permanent deformations. Though stiff and soft fender might have same deflection under same maximum reaction force acting on berthing vessel, amount of energy absorbed by stiff fenders is much higher than that of soft fenders. As a result, stiff fenders should be employed for berthing purpose.
On other hand, in mooring operations anywhere vessels are constantly subject to wave action, it is popular to keep tension force on the rope to a low value. In this relation, it is recommended to use elastic fenders.