Hawaiian scale is an expression of the height of a

wind wave In fluid dynamics, a wind wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result of the wind blowing over the water's surface. The contact distance in the direction of the wind is ...

affecting water. It is the expression conventionally used by

surfers Surfing is a surface water sport in which an individual, a surfer (or two in tandem surfing), uses a board to ride on the forward section, or face, of a moving wave of water, which usually carries the surfer towards the shore. Waves suita ...

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

and is also used in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

and parts of

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

. The expression, always given in feet, is a scaled figure corresponding to roughly half the actual measured or estimated height of a wave's face (trough to crest height). Thus, a "3-foot" wave is roughly six feet high (in actuality a height of ~1.8 m), ''i.e.'', head-high to a 6-foot (~180 cm) person; a "2-foot" wave is roughly four feet high (height of ~1.2 m), ''i.e.'', chest-high to such a person; and a "6- to 8-foot" wave would be 2 to approaching 3 times head-high to such a person (height of ~3.5 to 5 m). As wave height increases, however, so does the difficulty of judging that height, and as wave height approaches 20 feet (40 ft faces or 12 m height), the range of absolute wave heights corresponding to a given scaled expression tends to widen. The origin of the scale is obscure. Commentator Neal Miyake has proposed the following candidates: * Hawaiian lifeguards' announcement of smaller wave sizes in an effort to minimize casual tourists' interest in a surf break (albeit at the risk of attracting novice surfers aware of their own limitations who might be deterred by an announcement of a larger wave size) * A possible local practice of taking measurements "from the back" of the wave, ''i.e.'', from mean sea level (in technical terms, of measuring not the "peak-to-peak

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...

" of the wave or the height of the wave's face, the latter of which is increased by the wave's drawing water from in front of it as it breaks, but rather the wave's "semi-amplitude" or "peak amplitude"), or from wave buoy readings * Modesty or false modesty in early surfers' reports of their own accomplishments In Australia, which otherwise uses the

metric Metric or metrical may refer to: Measuring * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics ...

system, surfers and surfer-oriented media such as '' Australia's Surfing Life'' and '' Tracks'' magazines still measure and describe waves in terms of feet. Some journalists and media outlets that provide information to surfers but are not staffed by insiders to the sport express wave size in metric units using direct conversion from a literal interpretation of the scale's output, ''e.g.'', labeling as "1-metre" a wave that insiders would describe as "3-foot" or slightly larger. Such an attempt, however, is unsatisfactory both to surfers who do not use the converted units and to non-surfers and novices who do not realize that the trough-to-crest wave height is twice the figure quoted (in actuality, a H_m0 wave height of ~2 m from trough to crest).

Alternatives to the Hawaiian scale

Miyake reports that the Surf News Network expresses wave heights as "2/3 the height of the wave from crest to trough." This heuristic finds mathematical support as a compromise between two methods of expressing the combined effects of a wave's average upward and average downward deviations from mean sea level, namely ''a'') the sum of the absolute value of a sine wave's average (mean) deviation during its upward half-cycle and the absolute value of that mean deviation during its downward half-cycle (, 0.637, + , -0.637, ≈ 1.273)±0.637 is the approximate result when the integral from 0 to ''π'' or from ''π'' to 2''π'' of sin(''x'') is divided by ''π'', the length of the sine wave's half-cycle. and ''b'') the sum of the

root mean square In mathematics, the root mean square (abbrev. RMS, or rms) of a set of values is the square root of the set's mean square. Given a set x_i, its RMS is denoted as either x_\mathrm or \mathrm_x. The RMS is also known as the quadratic mean (denote ...

(RMS) amplitude of each of those half-cycles, ''i.e.'', twice the RMS amplitude of either half-cycle (2 .707≈ 1.4014), each of which expressions is within between 0.06 and 0.07, or within between 4.5% and 5.25%, of the value 1.3 yielded by the heuristic for that sine wave when is multiplied by the sine wave's crest-to-trough (peak-to-peak) amplitude of 2.

References

{{surfing-stub Surfing Surfing in Hawaii

Alternatives to the Hawaiian scale

See also

References