CETN I-63
March 1999
(navaids). The density and type of traffic (one- or two-way traffic), ship speed, turning basins,
and tug assistance are other factors that need to be considered in the operation of channels.
USACE defines navigation projects into two classes as follows:
"Deep-draft navigation refers to channel depths greater than 4.5 m (15 ft) and applies to
commercial seagoing vessels and Great Lake freighters, requiring cost sharing for depths in
excess of 6 m (20 ft). Shallow-draft implies channel depth being less than 4.5 m (15 ft) for
navigation, and 6 m (20 ft) for project cost sharing" (USACE 1994, 1995, 1999).
The above distinction is a practical criterion based on typical dimensions of ocean-going cargo
vessels. It is generally assumed that deep-draft ports connect with the oceans, seas, and Great
Lakes and serve seagoing vessels for trade/commerce and support various military functions. In
contrast, shallow-draft ports generally serve pleasure craft and/or private and commercial fishing
vessels, although these vessels can always utilize deep-draft channels. The USACE has
responsibility for maintaining more than 200 deep-draft and 600 shallow-draft ports and harbors.
WAVE PREDICTION FOR CHANNELS: Wave information is required for the design and
operation of entrance channels. The design vessel hydrodynamics and maneuvering
characteristics, size and orientation of the channel/waterway, and establishment of appropriate
navigational aids (navaids) are all dependent on the wave climate at the site. There are three
sources for wave information: field data, laboratory experiments (physical models), and
numerical modeling. In most cases, little (if any) wave data are available for engineering
planning and design studies. Wave transformation and ship response models have not to date
been fully incorporated into ship simulators. Because field observations are usually unavailable
and physical modeling of waves over large regions may exceed budget and time constraints, the
necessary wave information for entrance channels is often obtained from numerical wave
transformation models using wave hindcast data. Several numerical wave models, including
RCPWAVE, REFDIF/REFDIFS, STWAVE, and CGWAVE, are presently in use by USACE.
STWAVE and CGWAVE are integrated into the Surface-Water Modeling System (SMS) for
rapid grid generation and visualization of model results (Demirbilek and Panchang 1998).
The other aspect of wave information required for navigation channels, ports, and harbors deals
with the prediction of vessel motions and maneuvering characteristics. Wave and ship data must
be integrated into numerical (or physical) models that determine vessel hydrodynamic responses
and maneuvering behavior. The ability to do this requires the use of a well-tested and reliable
(numerical) ship response model.
A ship can undergo wave-induced motion in six degrees of freedom (DOF) as shown in Figure 2
(in general, six DOF motions apply to any rigid body). Three of the DOFs are in the vertical
plane (heave, roll, and pitch), while the remaining DOFs are in the horizontal plane (surge, sway,
and yaw). In naval architecture (Society of Naval Architects and Marine Engineers (SNAME)
1989), the motion (or response) amplitude for each DOF is usually normalized (divided) by the
incident wave amplitude and called a Response Amplitude Operator (RAO). The corresponding
RAO phase angle for each DOF is with respect to an incident wave crest at the center of gravity
of the ship. RAOs in the vertical plane contribute to the vessel underkeel clearance, defining the
channel depth requirements because of waves. The horizontal RAOs relate to the maneuvering
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