Navigating Among Coral Islands

Posted by Darrell Nicholson at 08:45AM - Comments: (5)

Photo courtesy Mahina Expeditions, www.mahina.com
Photo courtesy Mahina Expeditions, www.mahina.com

Ideally, you'll want to arrive with the sun high when navigating the coral passes of the Pacific.

For the average cruiser, the half-day passages pose a special challenge. The temptation is to leave early and knock out all the miles in daylight, but as the crew races against time, exhaustion can set in and the bad decisions multiply. Very often a better option is a night sail, leaving plenty of daylight hours to navigate into the new port.

The crew of Tanda Mailaika, a family of six whose 46-foot Leopard catamaran was lost on a reef on the southwest corner of Huahine in French Polynesia last month, learned this lesson the hard way. The loss is especially acute because, as the captain points out, it could have been avoided. The account of the wreck, provided by the skipper/owner Dan Govatos, and recorded in the podcast “Slow Boat Sailing” offers important lessons for cruising sailors.

The first error Govatos made was in planning the 80-nautical mile passage between Moorea and the anchorage Huahine. Anticipating the forecast winds of 20 knots from astern for most of the passage, he estimated about 10 hours for the passage, an average speed of 9-10 knots putting their arrival at 4 p.m., with plenty of light to enter Huahine’s reef pass. When the winds didn’t materialize, the crew ended up motorsailing for much of the passage—not reaching the southwest corner of Huahine until 9 p.m., well after dark. To complicate matters, the strong trades finally kicked in that night, creating an uncomfortable ride as they approached the island.

Lessons: Be extremely conservative when estimating speeds for a passage. It is much better to err on the slow side. You can almost always slow down or even heave-to, but it is much harder or impossible to make up for lost time. Likewise, allow a healthy margin for error in weather forecasts, particular in areas where meteorological data is spotty.

The second error was in the actual navigation. As the winds increased, Gavatos steered the catamaran close to Huahine and its steep-to fringing reef to get some shelter from the sea. According to him, the Navionics charts he was using misplaced the reef by about ¼-mile. So instead of 200 feet of water, they found themselves on the reef.

The atolls and volcanic islands of the Pacific rise steeply from the ocean floor, offering little warning. Although it may not be precisely plotted on every digital chart, Huahine’s fringing reef has appeared on charts for centuries, and any capable navigator who is paying attention should have no trouble avoiding it. As our special report on navigation pointed out (see “GPS Accuracy Can’t Replace the Navigator,” PS July 2015) even charts of more thoroughly surveyed errors can have gross errors that put sailors at risk, and the navigator needs to account for this.

As Gavatos relates, he saw the sounder indicate 85 feet and then decrease intermittently from there. At first, he assumed the sounder was incorrect—that some anomaly was creating a false reading (as had happened before).

Lessons: When navigating coral reefs at night, ¼ mile is cutting it too close. If you absolutely must hug the reef, you’ll want multiple navigation sources to confirm your position—your own senses being among them. Closed cockpits on big cats can take your senses out of action, a potential handicap when navigating near hazards (see “Multihull Madness,” PS March 2017). On the cruising website Noonsite, a Navionics spokesperson posted a response to the crew's comment that the reef was mischarted.

Although some boats can be salvaged from reefs, the Leopard’s cored laminate, an imperative on most multihulls, had no chance against the impact of a reef. I can only imagine the heartbreak of the crew as it filled with water.

Comments (5)

The storey is excellent and it noted that navigation is the key. In the Red Sea digital charts and GPS can actually place you between 1 and 2 nautical miles from your intended position. Care and visual reference is need when approaching an entry through a reef and it is preferable to have the sun behind you as this avoids glare from the water.
TedNobbs

Posted by: TedNobbs | August 15, 2017 7:14 PM    Report this comment

The storey is excellent and it noted that navigation is the key. In the Red Sea digital charts and GPS can actually place you between 1 and 2 nautical miles from your intended position. Care and visual reference is need when approaching an entry through a reef and it is preferable to have the sun behind you as this avoids glare from the water.
TedNobbs

Posted by: TedNobbs | August 15, 2017 7:14 PM    Report this comment

My wife and I have sailed our boat in French Polynesia for several years. We are deeply saddened by the loss of this family's boat and their journey aboard her. We wish them well and are happy that no one was physically injured. The French Polynesian rescue teams and Huahine locals showed both great competence and great compassion and we thank them for both.

We have seen wrecks on Huahine's reef many times since, during typhoon season, we store our boat on Raiatea, closest island to Huahine. Dominique Goche, the owner of the Raiatea Carenage, has performed almost 200 salvages of boats on reefs throughout his country, and he told us, "There are no uncharted reefs in French Polynesia." We believe him. We do know from personal experience that there are chart errors, but no uncharted reefs. Every mariner should know that there is not even a theoretical possibility of a perfectly accurate chart.

We have sailed among the many lovely Society Islands on many occasions through the years, and your analysis and prudent comments were, in our opinion, correct. Your suggestions should be followed by every boat (sail or power) traveling among coral islands, especially islands that are unknown. Our boat is a monohull so our five senses are exposed to the information provided by water and air and we note that even small ocean swell causes large and visible spray off the reef edge, and the pounding of the surf can be heard far off-shore. Even the smell of the islands provide proof of proximity. Seeing our forward-looking sonar display a reading of 85 feet or even 200 feet, while outside a reef, would be terrifying. The consequences of shallow water near a reef trump staying the course because of possible instrument error.

The western "nose" of Huahine's reef has caught more than one boat and should be avoided. Last season, a beautiful boat, S/V Exocet, sailed directly into that nose as they were following the island's reef toward the pass into Fare. The year prior to that, S/V Morning Dove went aground and was lost while sailing among the Tuamotus. These two groundings have many similarities. Had S/V Tanda Mailaika continued at the 200-foot contour, inevitably she would have grounded on the nose like so many others.

We would like to add our opinion to Practical Sailor's. Changing conditions often destroy carefully made plans for a passage. So be it. There is never a reason to be within a mile of a reef, and two miles are better. Reach the range mark alignment for your pass and make the turn. Your passage through the reef will use more time but your vessel and crew will have avoided grounding on a reef. In our opinion, the golden nugget of advice from the Practical Sailor analysis is to stay well offshore. Additionally, a mariner approaching a coral-surrounded island or atoll should "zoom in" and attend to the depth detail provided at this scale. S/he can acquire a sense of the depth around a reef and make plans to stay well away.

Sea room is a mariner's friend.

Posted by: AKCruiser | August 12, 2017 3:15 PM    Report this comment

All of those recommendations are good and prudent. We have seen boats lost every year we have been in the South Pacific. Some places like the French colonies have excellent charting. Some places like Tonga, Fiji and Vanuatu have charts based on Captain Cook's surveys. In Mexico we know of one island that is a mile and a half off. And there are places further afield that are much worse. What most of us do in remote coral islands is use some form of Google Earth charts (and be very conservative). We use KAP charts on OpenCPN but several other ways to do it.

Posted by: cpharry | August 10, 2017 4:55 PM    Report this comment

I am sorry for your loss. I hope everyone got off without injury. I sailed to Huahine from Raiatea in 2014 on a Moorings 48' catamaran but we approached from the west where there is a wider opening in the reef with 2 Passes, Avamoa and Avapehi. The eastern Passe Fararea and the southern Passe Ararra are less forgiving and I would not want to try to sail in my first time at night. Possibly changing course and sailing into Faararoa Bay on Raiatea would have been easier as the entrance is well marked out to the edge of the reef with lights but how would you know that on your first sail there. I use iNavX on my iPad and MacENC with Navionics Charts as well as the boats Raymarine chart plotter when I sail. The charts are all accurate but not accurate enough for night sailing around reefs. Best of luck with your next sail. "Stuff" happens.

Posted by: TimC | August 10, 2017 1:37 PM    Report this comment

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