Type of Fenders
The purpose of installing fenders on the pier is to protect the vessel and the pier from damage when the vessel berths alongside the pier. The fenders absorb the berthing energy of the vessel and soften the berthing impact on the pier. Fenders can be classified into timber fenders, rubber fenders and plastic fenders, according to the type of materials used.
Timber fenders are mainly produced from tropical hardwoods and such application is not environmentally friendly. There is also a high damage rate for the timber fenders due to wear and tear by vessels and this has resulted in substantial maintenance requirement. Hence, further use of timber fenders is not recommended.
Rubber fenders are produced from natural or synthetic rubber. Rubber fenders are available in a wide range of forms and dimensions designed to meet the requirements of a variety of operating conditions. They are designed to absorb the berthing energy by means of their deflection. Advice should always be sought from one or more of the major reputable suppliers regarding the energy absorption characteristics, fender reaction, deflection and other installation details.
Rubber fenders can be classified into two categories based on their performance. Buckling or constant reaction type fenders have a reaction load that increases more or less linearly in the initial stage of deflection as a result of elastic compressive deformation. However, when the reaction load reaches a certain magnitude, it tends to remain almost constant regardless of the increase in deflection due to elastic buckling, until the hollow portion of the fender is closed. After closure of the hollow portion of the fender, elastic compressive deformation is restored,resulting in further increase in the reaction load.
(1) Cell Fenders
Cell fenders and other large unit fenders are usually mounted individually in a series. Each of the fenders is designed to absorb the berthing vessel’s energy on its own.Steel frontal frames may be installed for load spreading to keep contact pressures within acceptable limits. In some fender systems, these unit fenders are connected together to provide a larger energy absorption capacity or to cover a larger operational range of vessels.
(2) Pneumatic and Foam-filled Fenders
Pneumatic and foam-filled fenders are characterized by their high energy absorption and low reaction force. Pneumatic fenders comprise a hollow rubber bag filled with air whereas foam-filled fenders comprise a resilient closed cell block covered by a reinforced rubber skin. These fenders are designed to absorb berthing energy by the work required to compress the air or foam cells.They are generally in the form of cylinders with domed ends floating in front of the berth structure. Chains or wire ropes with swivels and shackle connections are used to anchor the fenders to the berth structure.
(3) Long Strip Rubber Fenders
Long strip rubber fenders are more suitable for installation on piers designed for use by smaller vessels. They are generally more economical than the larger cell fenders and pneumatic or foam-filled fenders. Common forms of long strip fenders include cylindrical,D, arch and turtle fenders.Cylindrical fenders are usually supported on chains but can also be fixed in position.The energy absorption capacity is among the lowest of the long strip fenders for a given section height.D fenders differ from cylindrical fenders by having a flat surface to facilitate installation and therefore they can be directly fixed on the vertical surfaces of the piers. The curved contact surface provides a soft initial contact between the vessel and the berth structure. The area of contact increases with the energy absorbed during the berthing operation. Installation of arch fenders is relatively simple. The fenders can be fixed directly on the vertical surfaces of the piers.The energy absorption capacity provided is relatively high compared to other long strip fenders since the energy is absorbed mainly through compression deformation rather than deflection. The reaction force is also large,resulting in a relatively high contact pressure.
The turtle fender is a relatively new type of rubber fender designed for small craft port facilities, and is characterized by a wide protective area and a relatively large energy absorption capacity for a given section height. It possesses a large breadth to height ratio to minimize damage in severe mooring conditions. The large area of contact results in lower contact pressure for a given reaction force. Similar to the arch fender, each turtle fender can be fixed directly on the pier with two rows of fixing bolts.
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