12 December 2001
Determine level of accessibility; e.g. minimum of 339 days per year of
access to homeports and 300 days per year of access to shipyards and
ports of call. These accessibility levels equate to operational restrictions
of approximately 2 consecutive days per month of encroachment on the
underkeel clearance for homeports and 5 consecutive days per month for
shipyards and ports of call, respectively.
Based on local traffic and regulations, assume an average ship speed
through channel; e.g. 5 knots.
Using assumed transit speed and navigational charts, calculate the time
required to accomplish the transit from the outer channel to the turning
basin or berth.
Using the calculated transit time, days of accessibility, and the charts in
the Appendices, determine the channel depth requirement.
Subtract the water depth requirement from the channel depth requirement
to obtain the design water level. This number will usually be negative and
thus result in a design water level above MLLW.
For all berths, except turning basins use 0 m (0 ft). Since 1.83 m (6 ft)
of clearance is provided, as noted later, the design water level may equal the datum
Squat the downward displacement of a vessel while underway. Assume
no squat in berths. Appendices C - F incorporate squat for infinitely wide
channels with ship speeds equal to or less than 10 knots. Ship squat
greatly increases when CVNs transit channels less than 600 ft in width or
move at speeds faster than 10 knots. To determine squat for conditions
other than those addressed in Appendices C - F, use the method
contained in paragraph 5-18.104.22.168) of this manual. All channels used by
aircraft carriers in the United States, except the Southern Branch, Lower
Reach, of the Elizabeth River, Norfolk, VA (137.2 m (450 ft) at narrowest
point) and the Entrance Channel, Mayport, FL (152.4m (500 ft) at
narrowest point), are wide enough to be considered infinitely wide. For
these narrow channels, the squat increases by 0.6 m (2 ft) The water
depth requirement determined above should be modified to incorporate
any difference in calculated squat.
For outer channels, assume ship speed of 15 knots. For inner channels, base on local
traffic and regulations, but as a minimum, assume an average ship speed through
channel of 10 knots and include the effects of narrow channels as noted above. For
berths and special cases, assume ship speed of zero.
Ship motion -- vertical excursion of vessel from waves. Appendix E
addresses ship motions only for San Diego and Mayport. For other