experimental:

  travel times to kauai from 51101

            NW              N
        (315 degrees)  (360 degrees)

period      time           time
(sec)      (hours)        (hours)
 25         2.1            1.1
 20         2.6            1.2
 17         3.1            1.4
 14         3.8            1.7
 12         4.6            2.1

period      depth      speed
(sec)        (ft)      (mph)
 25          1646        87
 20          1053        70
 17          761         59
 14          516         49
 12          ---         40
 10          ---         34
 7           129         24.5

Sean Collins of Surfline:

The speed of travel of the deep water swell group will be 1.5 times the 
swell period; ie: a 20 second swell will be traveling at 30 Nautical 
mph. The actual individual waves will be traveling at three times the 
swell period, so a 20 second swell will have waves moving at up to 60 
Nautical mph.

The individual waves will travel to the front of the set as the swell 
group moves forward; once there, it'll slow down and drift to the back 
of the pack before moving forward again. Think of it as a conveyor belt 
turning at 30mph but the whole conveyor belt chassis is actually on the 
back of a flatbed truck going down the highway at 30mph. So if you had 
an object attached to the conveyor belt -- while it's turning and being 
carried by the truck -- the actual speed of the object would be 60mph. 
(Sound like math yet?)