28 July 2005
Efender = Cb x Cm x Eship
Efender = Energy to be absorbed by the fender system
= Berthing coefficient = Ce x Cg x Cd x Cc. Sometimes Eccentricity (Ce),
geometric (Cg), deformation (Cd), and configuration (Cc) coefficients are
combined into a single value called berthing coefficient.
= Effective mass or virtual mass coefficient
Each of these coefficients is discussed separately below.
c. Eccentricity Coefficient (Ce). During the berthing maneuver, when the
ship is not exactly parallel to the berthing line, not all the kinetic energy of
the ship will be transmitted to the fenders. Due to the reaction from the
fender, the ship will start to rotate around the contact point, thus
dissipating part of its energy. Treating the ship as a rigid rod of negligible
width in the analysis of the energy of impact on the fenders leads to the
Ce = k2/(a2 + k2)
k = Radius of longitudinal gyration of the ship, ft.
a = Distance between the ship's center of gravity and the point of contact on the
ship's side, projected onto the ship's longitudinal axis, ft.
Values of Ce typically are between 0.4 and 0.7. The values for Ce may be
computed from Figure 5-2.
d. Geometric Coefficient (Cg). The geometric coefficient, Cg, depends
upon the geometric configuration of the ship at the point of impact. It
varies from 0.85 for an increasing convex curvature to 1.25 for concave
curvature. Generally, 0.95 is ended for the impact point at or beyond the
quarter points of the ship, and 1.0 for broadside berthing in which contact
is made along the straight side.
e. Deformation Coefficient (Cd). This accounts for the energy reduction
effects due to local deformation of the ship's hull and deflection of the
whole ship along its longitudinal axis. The energy absorbed by the ship
depends on the relative stiffness of the ship and the obstruction. The