The Design Criteria for Marine Fender Systems
As the trend prevails toward the design and construction of offshore structures to serve large vessels and construction barges in exposed seas, it is considered necessary to assess and update the design criteria for marine fender systems
A marine fender system is a protective installation designed to prevent direct contact between ship and dock so that mechanical damage caused by impact and abrasion can be reduced to a minimum. An ideal fender system offers a sensitive response that increases proportionally to the excitations induced by a berthing or moored ship. Such a system absorbs high energy with low load transmission at reasonable construction and maintenance costs. Cost-effectiveness is an important criteria to be considered, including the expected loss of effectiveness because of physical and biological deterioration.
Based on the method of construction, the fender systems can be categorized into three classes defined as follows
- A fender system attached to a dock is a system designed for directly protecting ship and dock by absorbing impact energy, thus reducing lateral ship thrusts.
- A fender system detached from a dock is a system for indirectly protecting a dock by absorbing lateral ship thrusts, tending to permit a lighter dock design.
- A breasting-platform fender system is a series of independent breasting dolphirfs or platforms independent of a dock and is a variant of the detached fender system.
Analytical treatment and experimental investigation
The mathematical treatment of berthing ships was not systematically presented until Prof Vasco Costa published his paper in the Journal of Dock and Harbor Authority on “Berthing of Ships” in July 1964, and further discussed at the NATO Study Institution held in Lisbon in July, 1965, the Analytical Treatment of Problems of Berthing and Mooring Ships. Pertinent recommendations based on simplified analytical treatment have been made on how to maneuver a large ship to reduce berthing impact (Vasco Costa, 1968)
The complex nature of the berthing and mooring of ships can be well illustrated diagrammatically in the docking process of a ship. During the initial stage, the skills of the captain and pilot, together with the assistance given by the tugs and crew in mooring lines, all influence the berthing maneuvers.
Vasco Costa (1964, 1968) derived the dynamic equations based on the principles of conservation of angular momentum with respect to the point of contact, and of conservation of kinetic energy. The first principle permits the evaluation of the angular velocity (ω) with which the berthing ship will rotate about the point of contact. The energy equation will determine the effective kinetic energy to be absorbed by the fender system.