Is Shear Restraint Necessary for Fendering System Design?

All comments about the overestimation of design berthing energy inherent in the traditional energy calculation are based on the general practice, which does not adjust the calculated energy value by a further arbitrary service factor of at least 1.4, as stipulated by the British Standard.

At the same time, much design effort and significant cost is expended trying to restrain fenders, especially fixed fendering systems, from shear deflecting vertically and/or horizontally under the almost universal belief that shear simultaneous with normal deflection has a deleterious effect on a rubber fender’ s ability to perform its design function. In fact, up to at least 40 percent shear deflection there is no effect on performance or on useful fender life.

Adding shear restraints not only add cost, it is unnecessary, because they are incapable of stopping moving objects without physical damage. Without shear restraints, there is a greatly reduced chance of damage, and the fender will function optimally. If damage does occur, it will be less severe than if restraints are employed, so avoid shear restraints.

When designing a dock from scratch, the optimum solution is achieved by designing the fendering system in conjunction with the dock design process. This permits the coordination and optimization of all factors affecting dock and fender life: energy absorption, resisting the reaction force of the fenders and optimizing dock/fender geometry for the most effective operation.

The keys to designing a fendering system with optimal performance and minimal cost are:

• 1. Calculating design energy using no more than middle of the range values for velocity, hydrodynamic factor and construction factor.
• 2. Do not add a further safety factor.
• 3. Use a fixed fender or fendering system unless niche conditions indicate foam fender or pneumatic fender.
• 4. Do not use cylindrical fenders, if a rigid contact panel is employed, keep its face dimensions to the minimum consistent with typical hull frame spacing.

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