Waves: a Hawaiian surfer would call this a three-foot wave | Photo: Shutterstock

Why do the Hawaiians measure waves differently from the rest of the world? There are several theories as to why this happens.

Buzzy Trent once said that "waves are not measured in feet and inches; they are measured in increments of fear."

While that can be a savvy analysis, it is also true that we need to find ways of comparing different waves.

That is why we measure waves. We do it using the metric system (meter), the imperial system (foot), and the Hawaiian scale.

From an oceanographer's perspective, wave height is measured from the lowest part of the wave (trough) to the highest point of the wave (crest).

During the second half of the 20th century, surf culture developed its own measurement unit - the body height scale.

According to this unique visual unit of measure, you'll get around eight main typical wave sizes:

  • Ankle-high: one-foot waves;
  • Knee-high: two-foot waves;
  • Waist-high: three-foot waves;
  • Chest-high: four-foot waves;
  • Shoulder-high: four-to-five-foot waves;
  • Head-high: five-to-six-foot waves;
  • Overhead-high: six-to-11-foot waves;
  • Double overhead-high: 12-foot waves;

Traditionally, worldwide surfers tend to overestimate the size of the waves they ride.

Why? Fundamentally because it's human to overestimate our achievements, and our ego is always slightly bigger than the real deal.

On the opposite side of the spectrum, you'll find the Hawaiians, known for underestimating wave heights.

The Hawaiian scale is an alternative wave measurement scale expressed in feet that corresponds to roughly 50 percent of the average estimated height of a wave, from trough to crest.

As a result, an average surfer who believes he's ridden a 10-foot wave has, from a Hawaiian perspective, surfed a five-to-six-foot roller.

The World vs. Hawaii

So, why is the gap between the actual wave face observed by 99 percent of the surfing world and the Hawaiian readings so wide?

There are several possible explanations for such a dramatic difference.

Some Hawaiians say that it all started in the 1970s when local surfers called waves half as high as they were based on swell heights measured from the offshore buoys and delivered via marine forecasts.

In this case, an eight-foot groundswell at 20 seconds would produce real 15-foot wave faces, but Hawaiians would measure it using the original open ocean swell size, i.e., eight feet.

Others believe there's a reputational side to the Hawaiian wave scale.

Islanders like to impress foreign surfers and tourists by undervaluing wave height, thus showing bravery, fearlessness, badassery, and boldness.

There's also another theory that says that Hawaiians believe that a wave should be measured from its back, which almost always results in having smaller height measurements.

Last but not least, the conspiracy speculation - Hawaiian surfers and lifeguards say their waves are 50 percent smaller than they actually are to make their local surf breaks less attractive to haoles.

"It's two-foot out there. Not worth it."

Surfing: the alternative Hawaiian wave scales always underestimates the waves we've ridden | Photo: Shutterstock

The Larry Goddard Explanation

According to surf legend Larry Goddard, the Hawaiian scale, also known as the "Local Scale," was originally reported in "half meters" by observers working at the Kilauea Lighthouse on the north shore of Kauai.

They reported by teletype, sending their estimated wave heights, periods, and swell directions to the old US Weather Bureau Forecast Office in Honolulu.

"But, meters are pretty coarse units of measure, so the observers were instructed to convert the wave heights to metric, only in half-meter units. That's very close to about 20-inch units for each half meter," Goddard told SurferToday.

"So, two half meters is one meter, or about 3.28 feet - about waist high. Then, three half meters is about 60 inches or about head high. It looks like a five-foot wave, from the surfboard up to the lip of the wave."

"But the surfboard not at the bottom of the breaking wave - in the trough! If it were, the surfboard would not still be sliding downhill, down the face of the wave, right?"

"The true bottom of a head-high wave is at least another foot below the surfboard. It's a six-foot wave if you include the unrideable trough. Note that the true height in feet is about twice the Hawaiian scale, reported in half meters!"

Goddard says that the observers at Kilauea Lighthouse were estimating the wave heights. That is, they reported how big the waves looked to them.

"They were not surfers but, like most surfers, they ignored the trough, which is well out in front of the wave and not steep enough to ride," notes Goddard.

"If you include the trough, you will find that the true total wave height is about 20 percent higher, from top to bottom."

"So, a wave that looks like about five feet is actually about six feet if you include the trough at the exact bottom of the whole wave."

"To illustrate the half-meter scale, the best examples of wave heights to use would be either five feet, eight feet, or 10 feet because most surfers know that they are reported as "3," "5," and "6," so-called feet, which is actually half meters, not feet at all!"

"Thirty years ago, I realized that they were reporting only about 3/5 or 5/8 of the height that I had measured directly."

"If you take an average of 60 percent and 62.5 percent, you get 61.25 percent for the middle of the range of values, and that could be rounded off to about 61 percent, which was the ratio I used for some 35 years of doing surf forecasts for guys in Hawaii, who expected 'local scale,'" continues Larry Goddard.

"I would get feedback from various people and soon was able to see what their bias was. It was pretty wide-ranging in magnitude, but I could tailor my forecast to fit their own personal bias in wave height estimation."

"Everybody has some bias; the trick is to get your own eyes "calibrated" to reality. For that, you need to determine the actual height of a breaking wave."

"The best way to do that is to go out with a long pole and physically measure the height of waves on a given day at a particular surf spot, i.e., at any spot that has a hard, unchanging bottom where the waves break - not at a sandbar beach break."

"Then, you should also measure the depth of the water in the breaker zone at the exact lineup."

"With a gradually rising bottom, the top of a wave becomes unstable and breaks in water that is about 1.28 times the breaking wave height, so the wave height is about 0.78 times the water depth in the breaker zone," concludes the veteran surfer.

In the 1970s, Larry Goddard actually used a 14-foot-long bamboo pole with black tape spaced every 12 inches and white tape every five feet to measure his waves.

Is the Hawaiian wave height scale more or less scientifically accurate than the most used measurement standard adopted by surf forecasters? We may never know, so it's up to you to decide which one suits you.

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