The present article describes the more ordinary types of marine fender systems commonly used and the principles and characteristics of the major categories of fender systems in common use.
Description of various marine rubber fender systems
Marine fenders provide the necessary interface between berthing ships and berth structures. Therefore the principal function of fenders is to transform ships’ berthing energies into reactions which both the ships and berth structures can safely sustain. A properly designed fender system must therefore be able to gently stop a moving or berthing ship without damaging the ship, the berth structure or the fender. Once ships are safely moored, the rubber fenders should be able to protect the ships and the berth structures from the motions caused by wind, waves, current, tidal changes and loading or unloading of cargo. The design of fenders shall also take into account the importance of the consequences, suffered by the ship and the berthing structure in case of excessive ship berthing energy.
Marine Fender Systems can be categorized according to the mode by which they absorb or dissipate the kinetic energy of the berthing ship. Most fender systems are based primarily on the principle of the conversion of kinetic energy of the ship into potential energy of the rubber fender. Only a collapsible unit which dissipates the kinetic energy through the plastic deformation of steel or concrete between the rubber fender unit and berth structure, do not utilize this principle. Steel corrugated units are always used in conjunction with another type of rubber fender unit for which it serves as the energy absorbing equivalent of an electric fuse.
Other systems may exist which have either very limited application or have not been widely accepted. Also many existing rubber fender systems are variations or combinations of several of the systems listed. A single or easy solution to all rubber fender problems does not exist. Each combination of vessel, type of berth structure and berthing conditions has different requirements. Factors having impact on the choice of marine fender are: size of ships, navigation methods, location, tidal difference, water depths, etc. A ship berthing along an exposed berth structure will obviously have other demands on the rubber fender system than if it was to berth along a sheltered berth structure.
Contact us to get the lists the range of standard sizes, energy absorption capacities, reaction forces, rated maximum deflections etc. for the various types of ordinary rubber fender systems in use (jierfender@gmail.com). All are of the category that converts energy by elastic deformation. Rubber Fender manufacturers are constantly carrying out research and developing variations and improvements to these marine fender systems, so the fender system designer is advised to consult manufacturers regarding the availability of new rubber fender units. Also, the various fender manufacturers may have different names for marine fender units of similar appearance and performance characteristics.
Most of the characteristics are based on data published by marine fender unit manufacturers and actual fender performance may vary by as much as ten percent. Also, the characteristics are based on perpendicular impacts, and fender performance may vary considerably when subjected to angular impacts, which is the most common case.
For example, the different sizes of cylindrical fenders have, under side loading, a fender factors R/Ef varying from about 25 kN/kNm to about 1.3 Kn/kNm.
A rubber fender with 1500mm Outside Diameter (OD), 800mm Inside Diameter (ID) and 1500mm length will absorb an impact energy of 330 kNm at about 50% deflection. The resulting force to be resisted by the berth structure will be 90 kN with a fender factor R/Ef 900/330=2.7 Kn/kNm. What is interesting about these large marine fenders, which are designed for bigger ships, is that they have a high fender factor with low compression (at 10% compression R/Ef=14.0 – kN/kNm). Where smaller ships are concerned, they will have little energy-absorbing effect but function more as surface-protecting fenders. The curve shows that the fender factor decreases with increasing compression, as far as 50% when it is 2.7 kN/kNm. Beyond this the factor increases with increasing compression.
It must be realized that rubber fenders absorb energy even beyond “rated deflection” (defined by the manufacturers), but the forces to be resisted by the berth structures will then increase excessively. This is due to the fact that beyond “rated deflection” most rubber fenders begin to transmit more reaction rather than absorb more energy, usually.
As marine fenders or quays can only withstand a fixed reaction before failure, fender structures can be provided with devices or overload collapsible unit to prevent overload or damaging of the berth structure. The collapsible units can be constructed either in concrete or steel, and installed between the fender and the berth structure. To prevent failure or damage to the fender, the collapsible unit can be designed to collapse for a reaction force equal to the fender reaction at about 55 to 60% compression of the fender.
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