[Paddlewise] Breaking Waves Issue?

Paddlewisers,

I recently purchased and have been enjoying reading Sea Kayaker Magazine's
Handbook of Safety and Rescue by Doug Alderson and Michael Pardy. However,
something seemed unusual on page 48 as I read, "The crest will rise and
break when the depth of the water is approximately three-quarters of the
swell height. A 4-foot swell will break in water 3 feet deep. The height of
the wave at the time it breaks will be approximately 1.5 times its original
deep-water height. The 4-foot swell will rise to a 6-foot crest before
breaking in 3 feet of water."

I then checked a couple of other books I've read, and the information
conflicted. Derek Hutchinson in The Complete Book of Sea Kayaking wrote,
"When the depth is approximately one-and-a-half times the wave height, the
wave begins to break." Nigel Foster in Nigel Foster's Surf Kayaking wrote,
"The wave will steepen until the water is 1.3 times the height of the wave
at that time, when it will break."

Foster and Hutchinson's 1.3 to 1.5 times the depth of the water is not a big
difference, but Alderson and Pardy's .75 times is a big difference. Maybe
the real difference here is that Alderson and Pardy are referring to swells,
while Foster and Hutchinson are referring to waves. If that is the case,
Alderson and Pardy's number is .5 times when referring to waves and is even
a bigger difference.

Is there something else going on here that I am missing?

Duane Strosaker
Southern California
www.rollordrown.com
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