A COMPARISON OF OBSERVED AND HINDCAST WAVE CHARACTERISTICS 
OFF SOUTHERN NEW ENGLAND 
by 
Robert F. Dearduff 
Hydraulic Engineer, Research Division 
Beach Erosion Board 
The Beach Erosion Board in collaboration with the U. S. Navy Hydro- 
graphic Office conducted a series of tests to compare wave characteristics 
obtained simultaneously in deep water, in relatively shallow water, and 
computed by the revised Sverdrup-Munk method of wave hindcasting. 
The records for deep water were to be obtained at the Nantucket Light- 
ship (located some 0 miles southeast of Nantucket in about 180 feet of 
water) by means of a floating step-resistance gage held stationary by a 
damping disk; however this gage became inoperative due to short-circuiting 
during its calibration aboard ship. Consequently, wave measurements were 
made visually from the lightship. Some 116 observations (on a four-hour- 
interval basis) were made. Height observations were obtained by noting 
the rise and fall of the water against the wave staff, length observations 
by using the length of the ship and its various parts as a reference, and 
period observations by stopwatch, using the travel time of a floating 
object from crest to crest. In each case values were obtained as an 
average over a three-minute period. Although obviously a true average 
value was not obtained, the very small waves being neglected, this value 
is still probably somewhat less than the significant values. 
The records for relatively shallow water were obtained by a pressure- 
type recorder installed in 30 feet of water off Martha's Vineyard, 
Massachusetts. This recorder was operated intermittently over the period 
September 20 to October 9, 1951. Some 58 seven-minute records were made 
during this time, each recording representing a four-hour time interval. 
The locations at which waves were observed are shown on Figure 1. 
NANTUCKET LIGHTSHIP OBSERVATIONS* 
The Navy Hydrographic Office data are broken down into the two main 
divisions: Swell Waves and Local Wind Waves. However, an analysis of the 
data shows that there is no distinct line of demarcation between these, in- 
asmuch as waves of 2, 3 and -second periods are included in both divisions. 
h 
* "Preliminary Report, Nantucket Wave Observation Project, 19 Sept-9 Oct 1951," 
Navy Hydrographic Office (unpubl). 
