EM 1110-2-1100 (Part II)
30 Apr 02
(10) A number of quasi-empirical procedures for predicting vessel-generated wave heights have been
published (see Sorensen (1986) and Sorensen (1989) for a summary). Most procedures are restricted to a
certain class or classes of vessels and specific channel conditions. A comparison (Sorensen 1989) of
predicted Hm values for selected vessel speeds and water depths showed significant variation among the
results predicted by the various procedures. The best approach for design analyses appears to be to review
the published vessel wave measurement data to compare with the vessel, vessel speed, and channel conditions
that most closely approach the design condition and select a conservative value of Hm from these data. If this
is not possible, then the values in Table II-7-5 can be used as rough estimates for the different types of
vessels.
Table II-7-5
Selected Vessel-Generated Wave Heights (Sorensen 1973b)
Hm(m)
Hm(m)
Speed
at 30 m
at 150 m
Vessel
(m/s)
Cabin Cruiser
3.1
0.2
0.1
length-7.0 m
5.1
0.4
0.2
beam-2.5 m
draft-0.5 m
Coast Guard Cutter
3.1
0.2
0.3
length-12.2 m
5.11
0.5
beam-3.0 m
7.2
0.7
draft-1.1 m
Tugboat
3.1
0.2
0.1
length-13.7 m
5.1
0.5
0.3
beam-4.0 m
draft-1.8 m
Air-Sea Rescue Vessel
3.1
0.1
0.2
length-19.5 m
5.11
0.4
0.3
beam-3.9 m
7.2
0.6
draft-0.9 m
Fireboat
3.1
0.1
0.1
length-30.5 m
5.1
0.5
0.3
beam-8.5 m
7.2
0.9
0.8
draft-3.4 m
Tanker
7.2
0.5
length-153.6 m
9.3
1.6
beam-20.1 m
draft-8.5 m
Note: The above data are from tests conducted at water depths ranging from 11.9 to 12.8 m.
1
Denotes that the vessel was starting to plane.
b. Vessel motions.
(1) Response to waves.
(a) Wave action will excite a floating vessel to oscillate in one or more of six components of motion or
degrees of freedom. These are translated in the three coordinate directions (surge, sway, and heave) and
rotation around the three principal axes (roll, pitch, and yaw). Which of these motion components is excited
and to what extent depends primarily on the direction of wave incidence relative to the primary vessel axes
and on the incident wave frequency spectrum compared to the resonant frequencies of the six motion
components (Wehausen 1971). If the vessel is moored, the arrangement of the mooring lines and their
taughtness will influence the resonant periods and the response amplitudes of the vessel motions. If the vessel
is moving, the effective or encounter period of wave agitation is the wave period relative to the ship rather
than to a fixed observation point. Wave mass transport will also cause a slow drift of the vessel in the
direction of wave propagation.
(b) Small vessels, such as the recreational vessels found in marinas, will commonly respond to shorter
wind-wave periods. An analytical study, coupled with some field measurements for seven small boats
Harbor Hydrodynamics
II-7-57
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