Between The Marquesas and The Society Islands (where Tahiti is) is an archipelago of over 70 small, scattered islands. Called The Tuamotu Archipelago, this group of islands was unofficially called “The Dangerous Archipelago” for centuries due to the high risk it posed to mariners. Unlike the young, steep, lush islands of The Marquesas, the islands in the Tuamotus are nearing the end of their geological life cycle. They are coral atolls, which are basically just a ring of coral, the fringing reef for a volcanic island long ago collapsed back into the sea. There are typically motus (or islets) along the reef on the northern and western sides, and if there are any towns or villages this is where they would be. The motus are totally flat with little vegetation except for palm trees and short grass. The southern sides of the atolls are often just bare, awash coral reefs, so, as you can imagine, they can be difficult to see visually until you are right on top of them. They don’t give off a huge radar signature, so before GPS this entire archipelago was mostly avoided by cruisers due to the risk of going aground and being stranded or worse, sinking.
Today, a small subset of the atolls have become common cruising destinations on the way from The Marquesas to Tahiti. Others, while less common, can still find 10-20 boats per season visiting them. Still, the majority are avoided either because they are way out of the route, because their passes are either nonexistent or too harrowing to consider transiting, or because they are too close to the restricted zone where the French used to do nuclear testing.
In order to get into the lagoon within the coral ring of an atoll, there must be a pass that is safe enough to transit. Before I say a little about the passes, I want to point out that some of the atolls are HUGE, like 10-20 miles long and 5-8 miles across. So, if you are like me, when you think of the word “lagoon” you are thinking of a small pool, but no, these “lagoons” are massive. The passes are basically just gaps in the coral and they come in all lengths and widths. Some atolls have more than one pass, but many have only one. As the tide rises and falls it affects the current through the passes as the lagoon fills with the incoming tide and then empties with the outgoing tide. The ideal time to transit a pass is at slack tide with little to no wind. The worst conditions would be with a strong current in one direction and a strong wind in the opposite direction, because this creates the condition of standing waves, and sometimes they can be huge and therefore quite dangerous. Among our buddy boats (and I’m sure among most other cruisers) a lot of effort and energy went into trying to predict when slack tide would be for a particular pass. We would take the tide tables for Rangiroa (The capital of The Tuamotus) and then estimate based on difference of degrees latitude and also what the prevailing weather has been like. For example, if the wind has been blowing hard from the south, the lagoon may be fuller due to water coming in over the reef, so the outgoing tide may be more predominant and slack tide in the pass would be offset from what is predicted based solely on the tide tables. In fact, we went to an atoll that never has an incoming current in the pass (but that story won’t come until we get to The Societies).
So, first we would all try to predict, then we would consternate, because of course we would all come up with different answers, then after more stewing and calculating we would reach some sort of agreement on when we thought the best time to transit the pass would be on the day we thought we might arrive. Then, we had to actually arrive at that time. That’s a trick. We learned we could predict fairly close, but nothing beats getting out the binoculars and observing the pass conditions with your own eyes to determine if you think it’s safe or not. I don’t think we ever transited a pass at exactly slack tide, and we did usually encounter small standing waves, but we never had anything close to a scary moment.
Inside the lagoons is what may at first look like a huge pool clear water to sail about as you wish without the ocean swell to roll you about. However, in reality, the lagoons are littered with coral heads, many, if not most which are not charted. So, in order to move about, you need good visibility and a constant lookout posted on the bow, or higher up, if possible. You want the sun out, not clouded over, and you want it directly overhead or slightly behind you. The worst sun condition is to have it shining directly in front of you. Generally, the coral heads, affectionately called “bombies,” are near the surface, large, and easy to spot. But you never know when that small one not right at the surface but shallower than your draft would find its way in your path, so you had to stay diligent and maintain a good watch. Alex and Brenden proved that standing on the bow watching for bombies for hours at a time was not exactly their strong suit. “C’mon Brenden! At least have your eyes pointed somewhat in the direction of the water!”
Gresham Family Exodus 