Cracking The Code For Hawaiian Channel Crossings
The regular edition of the 5th Annual ʻAu I Nā Mokupuni ʻEkolu Maui Nui Swim is approaching on August 27th. It is a 3-day event that typically starts on the island of Maui in the state of Hawaii. The goal of the challenge is simple: swim across the three channels that separate the Hawaiian Islands of Maui, Molokai, and Lanai over a three-day period.
Each channel has its own unique attributes and strategies for a successful cross. Since its inception in 2017, 20 out of 23 entrants have successfully completed all three channels with several additional swimmers coming along for the adventure and completing a channel. Three swimmers have completed the event twice and one swimmer completed the event all four times it has been hosted.
Over the past two years, three attempts of the same format (outside of the above event) have been attempted unsuccessfully. The purpose of this report is to increase success among a growing open water swimming community through data sharing. Channel crossing data is increasingly more sophisticated especially with the tech open water swimmers regularly wear on their wrists. Comparisons to historical data is increasingly available. In select cases, comparisons to data from other channels can be made.
The Auau Channel separating the islands of Maui and Lanai has been crossed by swimmers hundreds of times. Given the wide range in ability of swimmers, it is difficult to compare total time and starting/landing points among such a diverse group of swimmers. Current methodology used in recording Hawaiian channel swims does not include swimmer experience, ability, and/or benchmarks for speed. In addition, it is uncommon for certifiers to include wind and tide data on certification forms. In general, most of the data includes start and end points and times. Ongoing effort is underway to add tide and moon phase data among others.
The chaos created by the combination of winds, currents, traffic, wildlife, and swimmer and crew factors leads to incredible variability in swimmer experience and is a constant threat to success. Control of such factors becomes more important when more events are scheduled ahead of time, especially if swimmers from remote areas are included. In current form, the channel crossing database does not allow for meaningful analysis to determine optimal conditions. Therefore, in this preliminary report data from one swimmer and/or the above event is referenced. Data from seven crossings shows that swimming Auau during a falling tide with a low tidal coefficient allows for the straightest course. The lowest tidal coefficients are prevalent around last quarter moons and low coefficients are also present during first quarter moons. Changes in currents are lowest in certain channels during periods of low tidal coefficients.
During a rising tide with a high tidal coefficient, the lateral excursion of channel swimmers is approximately 7-8 kilometers when swimming from either direction between Maui and Lanai. If swimmers must swim with these conditions, then it appears prudent to start from either Kapua on Lanai or from Olowalu on Maui. This way, swimmers can take full advantage of the strong westbound current. The straight-line distances become approximately 19 kilometers, however much of this is with current assistance. An argument can be made that even faster Auau Channel crossing times can be expected if mastery of this current assistance is achieved. By comparison, total distances often exceed 22 kilometers when trying to swim the shortest distance between islands since swimmers are swept one way in the channel and have to reverse direction against strong currents to reach the opposite shore. Undoubtedly, it is preferable to swim with the current even when total distances are significantly increased. Excellent and numerous examples of this concept can be seen by studying successful Strait of Gibraltar and Tsugaru Channel (shown on right below) crossings.
In general, the moon phases, tide cycles, and tidal coefficients will stay similar over a three-day period. Therefore, it is advised during rising tides and high tidal coefficients to somehow test the current direction and velocity prior to attempting the Auau Channel. This is best through relationships with local fishers who might be on the water the day before your swim.
Alternatively, the swimmer and crew might consider stopping mid-channel on the day of the swim, determining the current velocity, and then adjusting the starting point as discussed above. This is possible given tidal windows are approximately six hours and most crossings are between 4 and 6 hours. If one determines the currents are too strong for a swimmer/group of swimmers, then either the swim should be canceled or the starting point adjusted. Furthermore, feeding times should be minimized to avoid drifting along the course when not swimming. It is untenable to reattempt Auau the following days and expect easier or more favorable currents. In the case of the 3-day 3-channel format, the other channels should be considered, although scheduling the window around bad conditions should be wholly avoided in the first place.
This preliminary analysis of Auau Channel crossing data suggests the development of best practices is possible. Ongoing analysis of a near complete listing of all Auau Channel crossings is underway. One additional point is that the variability in completion time for Auau is much greater than that for either Kalohi or Pailolo Channels with the fastest time for Auau being 3 hours 10 minutes and the slowest time being 11 hours 13 minutes. It has been demonstrated that fast crossing times of Kalohi Channel are possible even when strong easterly winds are present. On the contrary, strong winds of any kind make crossing Pailolo Channel very difficult. The Kalohi Channel should be on the radar for accomplished channel swimmers and even those looking to start out in the sport.
Courtesy of Steven Minaglia, MD, MBA, FACS, FACOG, an Associate Professor in the Division of Urogynecology & Pelvic Reconstructive Surgery, Department of Obstetrics & Gynecology & Women’s Health at the John A. Burns School of Medicine, University of Hawaii, and the Associate Editor of the Journal of Female Pelvic Medicine & Reconstructive Surgery, The Official Journal of the American Urogynecologic Society.
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