James Rexroad

Refresher Course: The former yacht captain checks the sail trim (top); Neil O'Keefe readies to dive an as yet unnamed reef.

Plan B CHART YOUR OWN COURSE Go Wild Comox, British Columbia Desolation Sound Yacht Charters; 250-339-7222; www.desolationsound yachtcharters.com Go Exotic Phuket, Thailand Faraway Sailing and Diving; 011-66-76-22-0958; www.far-away.net Go Blue Blood Newport, Rhode Island Bareboat Sailing Charters; 800-661-4013; www.bareboatsailing.com Go Traditional British Virgin Islands BVI Yacht Charters; 284-494-4289; www.bviyachtcharters.com Go Cultural Corsica, Italy Sun Yachts; 800-772-3500; www.sunyachts.com Go Arctic Seaward, Alaska Sailing, Inc; 907-224-3160; www.sailinginc.com Go Fish Loreto, Baja California Baja Sailing; 800-398-6200; www.paddlingsouth.com Go Dive Uturoa, French Polynesia Sun Yachts; 800-772-3500; www.sunyachts.com

DAY ONE, 1000 hours. Wind NE 10–15 knots. Sky a brilliant blue with occasional silky white cumulus. Katkandu sits tied to the dock at Ambergris Caye.

By 1030 hours we're under way, motoring through a gap in the reef a half-mile offshore. We round up into the wind, hoist the sails, and set a course of 130 degrees for Lighthouse Reef, an atoll 40 nautical miles away. The seas are three to four feet, but Katkandu doesn't pitch or roll as a monohull would.

1510 hours. We sight Northern Caye, our anchorage for the night, on the horizon and tack to starboard. The turquoise waters inside the atoll are separated from the deep blue of the open ocean by an unbroken line of white waves crashing on the reef. We haven't seen another boat since we left Ambergris Caye.

1630 hours. We pass into the protected anchorage between two postcard-perfect islands, all white sand and breezy palms. On our port side, tiny Sandbore Caye is no more than an eighth of a mile long, with a lighthouse and a few wooden outbuildings. To starboard, Northern Caye is much larger, a few square miles of dense green mangroves, palms, and zericote trees. Once we've moored, we snorkel off the stern among purple sea fans; brain, stag, and elkhorn corals; hundreds of neon angelfish, damselfish, parrot fish; and a long, fat moray eel watching us from his hole.

Day two, 0800 hours. Wind 10-15 knots. Calm water in the anchorage. By noon we're 80 feet underwater on our first wall dive outside the reef (these distant atolls see so little scuba traffic that most of the dive sites have not been named). This is one of the most vital, pristine reefs I've ever been on, with rare black coral, still intact thanks to the dearth of divers, swaying in the current.

Day four, 1030 hours. Wind E 10 knots. Seas calm. Katkandu motors through a gap in the barrier reef between South Water Caye and Carrie Bow Caye as we pull on shortie wetsuits, weight belts, tanks, fins. As soon as we're over the dive spot we descend the wide steps built into the transom and jump scissor-legged into the 80-degree water. A moment later we're hovering weightlessly. On our right the sheer reef wall drops 1,000 feet; on our left is the seemingly bottomless open sea.

From the boat we've already seen amazing sealife: red-footed boobies, frigate birds, iguanas, crocodiles, mahimahi, flying fish. But the variety at the different depths on the reef makes the world above seem desertlike by comparison—nurse sharks, rays, spiny lobsters, tarpon, barracuda, hundreds of colorful reef fish, and a variety of corals, fans, and sponges. This is our fourth dive in four days—we've been to two other unnamed sites and to one called The Aquarium—each one better than the last. Here there is no damage from boat anchors or divers' fins.

Day five, 1600 hours. Wind 25 knots. We approach tiny Goffs Caye from the southwest through squalls and somehow avoid running aground. No more than a sand spit, the island sits precariously atop the reef, as though the next storm might wash it into the sea. A pod of a dozen or so dolphins greets us, leaping from the water and swimming under the forward trampoline, so close we could touch them if we leaned down. We anchor alone in the lee of the cay, pile into the inflatable dinghy, don our masks and fins, and spend the next hour swimming with dolphins.

Lee Carlson lives on the North Fork of Long Island and is a former editor of Skiing.