The Indo Full Moon Myth

Ben Freeston

by on

Updated 73d ago

From elderly fishermen plying the reef passes of Nias to local kids riding planks with nails for fins in Maluku and western surfers in the bars and clubs of Bali, there’s a single myth which binds traditional Indonesian culture with modern surfing. One which states that Indo sees its best and biggest swells in conjunction with the full moon.

Indonesian history is a seafaring one, but would have offered little insight to the origin of Roaring Forties swells that often occur more than 3000 miles away. As recently as 160-years-ago, the naturalist and global explorer Alfred Wallace could still only speculate that the local wave climate was dependent on the storms and seas of the southern ocean. Even this knowledge didn’t rule out a moon phase / swell connection. However science can.

Inconveniently for those looking for no more than a single annecdote this 'swell of the decade' at Kandui fell during the Waxing Gibbous phase of the moon.

Shedding light on the truth has only become recently possible. While the ancient Babylonians had gathered enough data to accurately predict the cycles of the moon, it’s only since the satellite era that we’ve had access to detailed analysis of local wave conditions. And combining our 35-year hourly archive of swell throughout the archipelago with the moon phase data, gives a clear understanding of the relationship between moon phases and swell height.

Analysis of 30 years of peak surf face height data shows nothing more than a hair's breadth between average wave heights for different moon phases. Analysing % occurrence of the larger swells or even the maximum swell also shows that there's no correlation between moon phase and swell size.

Analysis of 30 years of peak surf face height data shows nothing more than a hair's breadth between average wave heights for different moon phases. Analysing % occurrence of the larger swells or even the maximum swell also shows that there's no correlation between moon phase and swell size.

© 2017 - MSW

Whilst it is impossible to say how this misunderstanding arose – the gap between myth and science isn’t as large as we’d like to think. As a species we've always quested to understand the world around us and to establish cause, it is first essential to hypothesise. With the moon so readily understood as the driver of tides (which are themselves waves) it’s an obvious step to imagine it as a driver of the shorter period waves we surf. Without the abstract language of mathematics, myth can often withstand efforts to test its validity: Confirmation bias, the natural and hardwired tendency to see only data that confirms our theories, facilitates the longevity of the connection and explains its ready adoption by a new generation of visiting surfers. However you can clearly see from the data that the connection just doesn't exist.

So what should we take away from this? It’s certainly not a damnation of traditional knowledge or cultures. Polynesian oral histories of ocean navigation skills and techniques were often dismissed until we ‘discovered’ them to be true by successfully recreating them in modern times. It’s more instructional to understand that the truth of any given theory is in no way based on the number of people subscribing to it. This should be obvious: Faith aside, we can have no idea if there is a God – but we can be very confident that, whatever the reality, billions of us will fall on the wrong side of the history when the truth becomes clear. In the same way, there’s no pro surfer, contest director, or local legend whose opinions on surf forecasting should be considered divine. Absorb local knowledge, but research the theories and most importantly, test the facts yourself if you want to better understand surf forecasting and the ocean. If you want narrative to explain the past, this sort of connection might work for you, it you want to actively predict the future it won't. The full moon offers no more chance of great swell in Indo than any other phase. Enjoy them all.

Here's Desert Point. 9ft@17 seconds of raw ocean power during the waning cresent phase of the moon. One shot doesn't disprove the rule, but the data does.

Here's Desert Point. 9ft@17 seconds of raw ocean power during the waning cresent phase of the moon. One shot doesn't disprove the rule, but the data does.

© 2017 - Shogo

As I’ve explored this subject it’s become clear that this waves and moon connection isn’t unique to Indonesia among either traditional cultures or modern surfers. I’m fascinated by the origins of the story, particularly given that Indonesia, as a single nation, is a modern invention, yet this seems to have been pervasive throughout the archipelago for as long as anyone can remember. It’d be great to hear of your experiences of this theory there or elsewhere or from anyone who can throw further light on the subject. It’s particularly close to my heart as hearing this story first hand in Indonesia in the 1990’s was part of the catalyst for my personal journey to better understand the origin of waves. The name ‘magicseaweed’ was a sideways glance to these sorts of theories as I built a website for what I hoped would be a different approach to surf forecasting.

Cover image: The Bukit under the pump by Liquid Barrel