The Dangerous Islands
The Tuamotus have been known as the “Dangerous Archipelago” in the past due to their very low aspect and poor charts. The highest point on Hao is recorded as being only 3m above sea level. The coconut palms grow to about 15m. The atolls are difficult enough to spot during the day with good visibility and at night virtually impossible. The depth of the water gives no indication of your approach to an atoll as they are steep sea mounts with depths typically exceeding 1000m just 1 mile offshore. The raised reefs on the North and West coasts gives a fair radar return but the southern sides are typically very low or partially submerged and give very poor radar echoes. This season there have been two yachts lost on the reefs further north and west, that we know of.
However these days with satellite positioning and relatively good charts (provided you have up to date charts of course) navigating between the atolls is a much safer affair than in the “olden” days. Of course nothing has changed once landfall has been made, the pass still has to be located and negotiated and all the corral heads avoided until a safe anchorage is reached. Eyeball navigation rules in the atolls.
We arrived at Hao atoll at daybreak on Tuesday 17th May. Two other boats arrived at about the same time “Randivag” a Swedish yacht was just ahead of us and “AdiejeWah” a Dutch boat was just behind us. A French yacht “Reggae” was a little ahead of us all but went to atoll Amanu just to the north of Hao. All four of us had departed the Gambiers within a couple of hours of each other. We were happy that we had kept up with the other boats all bigger than “.
The wind was within 20 degrees of dead astern for the whole passage of just under 500miles. We sailed the whole way with the #3 jib poled out and the main prevented all the way out on the other board. We gybed twice on the passage and shook or tucked a reef on the main a couple of time to adjust for wind and/or sea state, other than that it was uneventful. One afternoon we saw a large ray of some sort with a 2m wingspan just behind Morgane but were not able to identify it.
There is only one ocean pass breaching the reef around Hao’s lagoon so the tidal currents can be ferocious reaching rates of 20knots in extreme circumstances. We had kept a radio sked with “Randivag” and “AdiejeWah” on the passage and there had had been quite a lot of discussion about the time of slack water in the pass. Between us we had various guides, sailing directions and pilots which all gave different methods of estimating slack water in the Tuamotu passes. Solving all of the methods gave a fistful of results; discarding a couple of outliers the rest almost agreed on a time around 10:45 local in the morning. We were early so all three boats hung about outside and waited. We had a little look in out of curiosity and found quite an impressive rip running out. Randivag headed in about 40 minutes later and reported no more than 2.5knots of counter current so we followed along, the current pushing us sideways significantly but there is a very good set of leading marks to help keep you in the centre of the pass.
Incidentally the methods that gave the best time for slack water were the Sailing directions which give the slack waters as 4.5 & 2 hours before moonrise and the universal statement that in oceanic areas high tide slack will occur within 2 hours of the moon’s meridian passage. The problem with predicting slack water in the atoll passes is that the swell normally washes over the lower sections of the reef filling the lagoon so there is always more water flowing out of the lagoon than into it. Periods of heavy weather can pump even more water over the reef and in some cases this can cause a situation where there is no incoming tidal flow. In any case the period of incoming tidal current is usually shorter than the nominal 6 hours. In atolls such as Hao with only one pass the effect of all of the above is magnified.
We have also now been given a copy of a spreadsheet the “Guesstimator” (http://VofJ.blogspot.com) which takes a basic tidal harmonic for one port in the Tuamotus and applies a slew of fudge factors to produce a very fine sinusoidal current curve for many of the passes in the group. It seems accurate enough for at least the first slack water of a cycle where the current changes from outflow to inflow. I have my doubts about the second slack water though.
In any case the old standard of knowing more or less how tides work, the nautical almanac, for moonrise, moonset and meridian passage and applying our own version of the fudge factors produced the same result.
The atoll of Hao is located in the south central sector of the Tuamotu group. It is the fourth largest atoll in French Polynesia with a lagoon area of around 720 square km and with 47 square km of land surrounding the lagoon. The atoll is home to a large runway built to support the French nuclear bomb testing at Mururoa. The large military base (which, I read somewhere, at its peak numbered 6000 personnel) was shut down long ago and most of the buildings removed. All that remains is the runway, control tower and a few other support buildings and small contingent of troops tasked with completing the rehabilitation of the area vacated.
We are moored in one of the left-overs from the military base, the small boat harbour, which provides a save mooring with space for five or six yachts to lay alongside, more if rafted up. Weeds grow up through the expansion joints in the concrete and kids dive off a ramshackle jetty head at lunch time but it’s not hard to image the little harbour packed with patrol boats tasked with keeping Greenpeace, the Soviets and whoever else at bay. Closer to the airport is a larger port that is soon to be given a new life as a Chinese company is building a fish farm within the atoll.
The main village on the atoll is Otepa which is home to about 1000 souls. There are three shops a couple of snack bars, a large school and a college (children from other atolls come here), a few churches and that is about it. The roads are surprisingly good, many the legacy of the military base. We have dug out our bikes, from their very inconvenient storage area under the cockpit, and cycled many km to explore the reef.
The population is very friendly and everybody greets everybody else with a cheerful “bon jour” or “Iorana”. They are preparing for a season of festivities in June, building stages and kiosks for a carnival and the racing canoe crews are practicing their strokes.
As we cycle we hear numerous land crabs scuttling off and often see them racing across the road escaping from our path, claws held aloft in defence or defiance.
The coral inside the lagoon is in a bad way, most of it dead and algae covered, but there are some nice live patches and plenty of fish to see whilst snorkelling. There are lots of black tipped reef sharks patrolling the shallows.
There is a vague Falklands connection with Hao in that Louis Antoine de Bougainville visited during his circumnavigation and named it Harp Island.