There is a relation between the period of waves, their length and their speed, provided that the depth
is more than half the wavelength.
In metric units, wave length in metres=1.56 * period (squared) in seconds
In feet, wave legth = 4.5 * period squared
And the speed in knots= 3 * period in seconds
Waves with 10 seconds period are roughly 150m or 450 feet long and propagate at 30 kts.
If the depth
is less, the length and the speed are reduced.