3 October 2005
INTRODUCTION. A ship moving through the water generates several
types of waves that may have an effect on moored ships, structures, shoreline erosion,
SHIP WAVES. Two of the most noticeable waves generated by moving
ships are the diverging (or bow wave) and transverse wave (Figure 10-1). These waves
intersect to form a cusp line and then the size of the highest generated wave tends to
decrease as the distance from the sailing line increases. Characteristics of the ship-
generated waves is a complex function of ship shape, water depth, ship speed, etc.
NFESC TR-6022-OCN summarizes measurements and recent findings on ship waves
for ship hull-forms, such as those illustrated in Figure 10-2.
A spreadsheet SHIP-WAVE.XLS is available for making ship wave
predictions. This spread sheet takes the measurements from a wide range of physical
ship wave measurements and uses one type of Froude scaling to predict maximum
wave height one wave length away from the ship sailing line for a ship of interest.
Figure 10-3, for example, shows the minimum ship speed required to
generate a given maximum wave height one wave length away from the ship sailing
line. The x-axis of this figure is water depth. The y-axis of this figure is ship speed.
Contours are for selected maximum wave heights. For deep water (the right side of this
figure), the wave height generally increases as the ship speed increases for the range
of conditions shown. In shallow water the wave height contours are much closer
together at higher speeds. This shows that in shallow water a small increase in ship
speed produces a dramatic increase in wave height.
The spreadsheet SHIP-WAVE.XLS and NFESC report TR-6022-OCN
provides additional information on waves generated by surface ships.