UFC 4-150-06
12 December 2001
minimums to be used in preliminary harbor planning, but still subject to
detailed follow-up analysis, use the following approximations:
Vessel Type
Channel Depth
CV & AOE
13.7 m (45 ft)
CG
10.97 m (36 ft)
Destroyers, submarines,
Maximum navigational
and auxiliary ships
draft plus 1.5 m (5 ft)
Small craft
3.65 to 4.6 m (12 to 15 ft )
5-6.1.2.3
Detail Depth Design. The depth of the channel is determined by adding
the estimated maximum vessel draft and bottom clearance relative to a design still
water level (SWL). The maximum vessel draft is obtained by considering the various
factors given in Figure 5-3: salinity effects, loading effects, wave effects, and ship
motion and squat effects.
Static Draft. The extreme draft of a vessel at rest in still water is
equivalent to the distance from the water surface to its lowest underwater
extremity. The value for the maximum loaded draft of an undamaged
vessel must be adjusted to account for list, trim, and water density
changes. Values using these adjustments for critical situations need to be
verified through the using component. Preliminary estimates show the
following: list is 3 degrees, trim 4 inches per 100 feet of vessel length
stern down, and salt water-to-fresh water transition sinkage equals 2
percent draft increase.
Wave Motion. In cases where a vessel is in a water area that is subject to
wave action, vertical motions will increase the extreme draft relative to the
still water level. Rotational motions of pitch and roll, as well as vertical
displacement through heaving motion, will take place. The motion of the
ship subjected to steep waves requires that a dynamic analysis take into
account the physical property of the ship modeled in the sea condition.
Under certain critical ratios of vessel length to relative wavelength, the
added vertical sinkage of the vessel can be appreciably greater than the
water-level displacement at the wave trough. Generally, these critical
ratios are generally believed to lie within the 0.3 to 0.6 range. This
situation is normally critical where the unprotected harbor-entrance
approach is situated in shoaling water. A recent harbor site selection at a
particularly stormy site suggests that an overdepth in the approach and
entrance channels on the order of 35% of the draft is required. In semi-
protected water areas, such as when a ship is subjected to swell, but not
to local seas, the increased displacement of the vessel due to pitch and
heave can be determined by placing two points of the vessel on a
trochoidal wave surface at two-thirds the vessel waterline-length normal to
5-11
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