atoll pass

Answer
An atoll pass, also known as a reef pass or channel, is a navigable opening or break in the coral reef surrounding a lagoon of an atoll island. These passes are crucial for boats and ships to enter and exit the lagoon safely.

Key Points about Atoll Passes

  • Atolls are ring-shaped coral reef islands that enclose a lagoon in the center. Many atolls have one or more passes that allow water exchange between the lagoon and the open ocean.
  • The water flow through these passes can be extremely strong, with currents reaching up to 9 knots (around 16 km/h or 10 mph) during tidal changes. These powerful currents make navigating the passes very dangerous if not timed correctly.
  • The safest time to transit an atoll pass is during "slack water" when there is little or no current flow. This occurs around the times of high tide and low tide when the water levels inside and outside the lagoon are equal.
  • Attempting to enter or exit a pass at the wrong time can result in boats being swept onto the reef or out to the open ocean with no control due to the extreme currents.
  • Factors like the size of the lagoon, the number and width of passes, swell conditions, and weather can affect the timing and strength of currents in each pass.
  • Planning atoll pass transits requires carefully calculating slack water times, often using a combination of tide tables, guidebooks, software tools, and local knowledge. Even then, the timing can be inaccurate, so visually checking conditions is crucial.
In summary, navigating atoll passes requires precise timing to avoid getting caught in potentially deadly currents. Careful planning and respecting the power of the water flow in these passes is essential for safe lagoon entries and exits.
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