ERDC/CHL CHETN- IX-7
December 2001
(approximately one-third of the Corps O&M budget) on dredging. Thus, the dilemma is to
minimize the hUKC and corresponding costs while still ensuring safe navigation.
Available guidance for predicting hUKC is inadequate as there is little field and laboratory data or
numerical models to improve and validate this guidance. For the hWA component, EM 1110-2-
1613 (HQUSACE 1995) recommends a value equal to 1.2 times the incident wave height HI,
whereas the Permanent International Association of Navigation Congresses (1997) recommends
a value up to 0.4 times the ships' draft T. Typical harbors operate with 1.2 m (4 ft) # hWA # 2.4
m (8 ft), regardless of ship draft and wave height. Individual states have their own guidelines
that may differ substantially from each other. For example, the Hawaii Department of
Transportation recommends a hUKC of 1.8 m (6 ft) in the entrance channel, compared to 2.4 m (8
ft) by the Corps. This 0.6-m (2-ft) difference significantly increases the cost of project and
maintenance dredging.
Realistic and accurate measurement of vessel motions in prototype and at laboratory scales is
critical to developing improved deep-draft design guidance. Prototype ship motions and
environmental data were obtained in the unconfined entrance channel at Barbers Point Harbor,
HI in May 1999 for five ships. These field measurements were reproduced in a controlled
laboratory study of Barbers Point Harbor for one of the ships. The purpose of this CHETN is to
document comparisons between the laboratory and field measurements of wave-induced vertical
ship motions and define any scale effects that may exist. Good comparisons will validate the
physical model as a predictive tool for these vertical ship motions and, more importantly, hUKC.
The goal of this research is to develop data to improve the U.S. Army Engineer Research and
Development Center (ERDC) ship simulator and provide an empirical approach to aid in coastal
entrance channel design. Limited field and laboratory measurements of wave-induced, vertical
ship motions have been made at Barbers Point. Deterministic design curves will be provided
from these empirical data. Ultimately, a probabilistic model for predicting the total underkeel
clearance allowance hUKC that includes hWA, hTI, and hSQ must be developed to account for the
random nature of ship transits in entrance channels. Borgman (2001) has proposed a novel
approach for dealing with the statistics from this laboratory data that can extend their use for
different ships.
FIELD STUDY
Barbers Point Harbor: The Barbers Point Harbor is located on the southwest coastline of
Oahu (Figure 1) and consists of a deep-draft harbor, barge basin, resort marina, and entrance
channel (Briggs et al. 1994). The deep-draft harbor has an area of 0.364 km2 (90 acres) and is
11.6 m (38 ft) deep. A harbor extension was added in 1998. The barge basin is 67.1 m (220 ft)
by 396.2 m (1,300 ft) and 7.0 m (23 ft) deep. The West Beach Marina has a depth of 4.6 m
(15 ft) and was designed to accommodate 350 to 500 small boats. The entrance channel is
137.2 m (450 ft) wide, 1158.2 m (3,800 ft) long, and 12.8 m (42 ft) deep. It has a trench cross-
section, with sloping sides that intersect the existing bathymetry along its length. Stations were
located every 30.5 m (100 ft) along the channel for ship positioning. Sta 0 is located at the
offshore end of the channel, approximately 243.8 m (800 ft) from the 100-ft (30.5-m) depth
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