Swell Speed

The table below shows how fast open ocean swell moves at different periods.  See assumptions below for detail.

Period Speed (kts) Speed (mph) Speed (kph) Travel to Time 60 miles Depth of Swell (ft)
10sec 15 17.26 18:43 3:29 256ft
11 16.5 18.99 13:26 3:10 310
12 18 20.71 8:09 2:54 369
13 19.5 22.44 2:38 2:40 433
14 21 24.17 21:21 2:29 502
15 22.5 25.89 16:04 2:19 576
16 24 27.62 10:48 2:10 655
17 25.5 29.34 5:31 2:03 740
18 27 31.07 0:00 1:56 829
19 28.5 32.8 18:43 1:50 924
20 30 34.52 13:26 1:44 1,024
21 31.5 36.25 8:09 1:39 1,129
23 34.5 39.7 21:21 1:31 1,354
24 36 41.43 16:04 1:27 1,475
25 37.5 43.15 10:48 1:23 1,600

Assumptions:

Open ocean swell moves at Period x 1.5kts.  Example – 10sec Period = 10 x 1.5 = 18kts.

Depth of Swell is the depth at which the swell will begin hitting the ocean floor and start getting wonky.  (Period x Period) x 2.56

1 Knot = 1.15078 miles per hour.

1 Knot = 1.852 kilometers per hour.

Most of this info regurgitated from here: http://www.surfline.com/surfology/surfology_forecast2.cfm