UFC 4-152-01
28 July 2005
Formulas for computing the added mass coefficient, such as Equation 5-6
from PIANC, predict a narrow range of values for Cm, 1.5 for a draft- to-
depth ratio of 2.0 and 1.8 for draft- to- depth ratio of 1.1. PIANC
recognizes that some investigators have obtained larger values for added
mass coefficients but suggests that these results from small-scale tests do
not accurately model full scale conditions.
h. Berthing or Approach Velocity (v). It should be noted that the kinetic
energy of the berthing ship is a function of the square of the normal
component of its approach velocity. Thus, the kinetic energy, as well as
the resultant force on the berthing structure, is sensitive to changes in
approach velocity. By doubling the design value of the approach velocity,
the ship's kinetic energy is quadrupled. Design values used for the
approach velocity normal to the berth may vary from 0.25 to 1.50 fps
(0.076 to 0.46 m/sec), depending on the size of the ship being docked and
the tug assistance that is employed. Larger vessels with adequate
tugboat assistance can generally berth gently and the lower design
velocity may be used. Smaller vessels that self-dock may approach the
wharf at considerably higher speeds and, accordingly, the higher design
velocity should be used. The berthing velocity is also affected by the
difficulty of the approach, maneuvering space for tugs (slip width), and
location of the pier or wharf facility. Anticipate higher approach velocities
when the berth is located in exposed waters where environmental loads
cause difficulty in controlling the ship. Also, currents in tidal estuaries in
protected waters can be of major concern. Approach velocity normal to
the berth may be taken from Figures 5-3 and 5-4. Determining whether a
facility is "exposed," "moderate," or "sheltered" depends on the
environmental conditions at the site and is a matter for professional
judgment by the designer. Most naval facilities in the United States are
situated in protected waters and can be taken as "sheltered." Where high
currents (0.3 fps [0.091 m/sec] or more) or strong winds (40 knots [20.4
m/s] or more) occur frequently, a "moderate" condition should be
assumed. The "exposed" condition may be used when unusually severe
currents and winds are present. However, local experience with ship
berthing should control the selection.
104
Previous Page
