Surfable Wave Speed

Using the equation below and Table 8-4 at the bottom of this post, the estimated shoreward speed of a good, surfable 6-foot wave would be approximately 11 mph.

Surfing waves would be shallow water waves.  You can calculate approximate shallow water wave velocity with the second equation below.

Where v = velocity, g = gravitational acceleration, d = depth and λ is wavelength.

Based on the table below, I would say good surfing waves are "plunging" waves.  The table provides ratios of water depth to wave heights for different types of breaker waves.  A simple calculation where d = water depth and h = wave height can be used to estimate water depth for the different the types of wave described in the table.  For plunging waves, a 6-foot wave would break in 

d/h = 0.9

d/6 = 0.9

d = 0.9 x 6 = 5.4 ft of water.

Use 5.4 feet for d (depth) in the shallow water wave velocity equation above.  Velocity of a 6-foot wave moving toward shore would be aproximately 13.1 mph.

For an expanded discussion about wave and surfing speeds, click the following link:
http://bgsurfphysics.blogspot.com/2018/08/wave-surfing-speeds.html

Wave Velocities (C) for Selected Wave Heights and Types