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A vessel transfers its kinetic energy to surrounding environment.
A berthing vessel can only come to rest by transferring all its “motion energy” or “kinetic energy” to
the surrounding environment. This motion or kinetic energy must be absorbed and dissipated by:
a) The sea
b) Elasticity of the fender
c) Elastic deformation of the vessel’s hull
d) Elastic deformation of the pier
As evidenced by ships and harbors around the world, if the sea and fendering do not use their
maximum energy absorbing capabilities, damage can result to vessel, berthing structure, or both.
Proper fender needs to absorb vessel’s kinetic energy.
When a marine fender is struck, it deflects. This deflection is proportional to the amount of kinetic
energy it must absorb. As the fender deflects, it offers increasing resistance which is measured as a
reaction load. This growing resistance by the deflecting fender is experienced by both the pier and the
vessel’s hull. A proper fender should be capable of absorbing this kinetic energy without offering a
resistance so high that it might lead to structural damage of either the pier or vessel hull. Usually
damage will occur when the fender is too small to absorb the resistance.
Energy absorption is equal to the fender’s deflection, times its resistance to deflection. When a
fender can only offer a small amount of deflection compared to the vessel’s kinetic energy demands
placed upon it, higher resistances result. This means, once the fender can deflect no further, the
remaining kinetic energy is transferred to the pier and ship’s hull. This can lead to berthing damage.
1.DETERMINING ABSORBED ENERGY OF A BERTHING SHIP
The absorbed energy of a berthing ship can be made by the following methods:
a) Kinetic Energy Method
b) Statistical Method
c) Scale Model Tests
d) Mathematical Modeling
The most commonly used approach is the KINETIC ENERGY METHOD. It is the traditional method and
is subject to the judgement of the designer, however, it is time tested and seems to account for the
major variables influencing vessel berthing.
The Kinetic Energy of the berthing ship is calculated using the formula:
EShip = 1/2 MV 2
Where EShip = Energy on Berthing
M = Mass or Water displacement of the ship
V = Approach Velocity of the ship at the moment of impact with the fender
This energy must be factored up or down, depending on rotation of the vessel on impact, the amount
of water moving with the vessel thereby adding to its mass, the deformation of the ship's hull and the
berth type.
Calculating Fendering System Requirements
KINETIC
ENERGY DOCK
APPROACHING
SHIP
DEFLECTION
OF BUMPER DOCK
SHIP
DOCK
SHIP
REACTION
FORCE
REACTION
FORCE
Generally, larger fenders offer greater energy
absorption and lower reaction force compared to
smaller fenders with the same geometry.
ENERGY ABSORPTION CAPABILITIES
CORRESPONDING REACTION FORCE
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