January 8, 2004
What goes up, must come down. In 1687, Sir Isaac Newton explained the theory behind gravitational attraction in his major work, "Principia". But King Canute, the Danish conqueror of England, had provided practical proof of gravity's effect on the world's oceans almost seven centuries before. He set up his throne on the beach at low tide and ended up getting his feet wet; the water rose despite his royal presence. Like Canute, we've developed a great respect for the gravitational forces that cause fluctuations in the level of the sea. As Nathaniel Bowditch ("The American Practical Navigator") asserted in his introductory comments on tides, they "can be either a help or hindrance to the mariner" - an understatement if there's ever been one.
When we sailed in the Great Lakes -- before we took off to go cruising full time -- the water tended to stay in place. Sure, lake levels fluctuate, but we usually felt we could leave the boat at the dock, go for lunch, and return to find it more or less where we had left it. It was a different story when we headed out into the salt chuck. Just when we figured we had lots of water under us, it would begin to disappear. Not too disconcerting in Chesapeake Bay, where the tidal range typically is only a couple of feet, but more unnerving in coastal South Carolina and Georgia, where an eight or nine foot range is not unusual.
We remember anchoring in a creek near Hilton Head, South Carolina, and going ashore to visit with our cruising friends Harvey and Gerbrig, who were staying in a timeshare condo for a few days. When we got back to the boat, everything seemed normal except that a number of objects down below had fallen off the shelves. At first we thought we had been ransacked by intruders, but soon realized that, in our absence, the boat had careened itself at low water. We had returned at high tide and had missed all the excitement -- which is probably just as well since life at a forty-five degree angle can be a bit uncomfortable.
Sometimes you want to careen your boat on purpose. When David was cruising the south Pacific in the 80's, he stopped in at the Galapagos Islands to do some maintenance work on the bottom. There weren't any haulout facilities at Puerto Ayora on Isla Santa Cruz, but the locals offered him free use of a tidal grid in the inner harbour. It just happened to be a spring tide. The operation was a qualified success. David and his crew got the boat positioned correctly as the tide began to fall, but neglected to empty out the forward chain locker. While they furiously scraped and painted, the bow gradually nosed downwards until it was buried in the mud, somewhat compromising the quality of the final paint job.
The tidal range in the Bahamas, where we're now cruising, is generally around three feet or less. Not much compared to the fifty foot tides in the Bay of Fundy, but significant nonetheless given the skinny nature of the water in this part of the world. "Little Gidding" draws five feet (or at least she did before we loaded her up with a bunch of cruising equipment and enough stores to take us into the next century). We wouldn't want to have a draft much deeper than this when cruising the Bahamas. We can squeeze into a lot of anchorages, but shallower draft vessels have access to even more. (We expect this is one of the reasons behind the growing popularity of multi-hull boats here and elsewhere.) For us, the state of the tide often determines whether or not we visit a particular place.
We've spent the past week or so at Green Turtle Cay in the Abacos island group in the northern Bahamas. The anchorage in front of New Plymouth, the island's main settlement, is fine in settled weather, but exposed when the wind clocks with a frontal passage. Unfortunately, at this time of the year, cold fronts are a weekly occurrence. Consequently, most boats choose to anchor in White Sound, a watery cul-de-sac northwest of New Plymouth. Access to White Sound is via a half mile long marked channel. We checked our cruising guide when we arrived at Green Turtle on December 30th and were assured that the minimum channel depth at mean low water is four and a half feet. "Not a problem," David said confidently. "We'll have plenty of water if we wait 'til high tide."
The tide tables promised a high tide of 3.6 feet at 1328. Theoretically, this would give us over eight feet of water in total. We motored between the first set of channel markers a few minutes after high tide. The numbers on the depth sounder promptly plummeted; within a couple of boat lengths there was less than a foot of water under the keel. The screen briefly flat-lined. Eileen immediately cut the throttle. "What happened to all that water you were talking about?" she complained. "Maybe the channel got rearranged with the last hurricane," David mumbled. With our eyes glued to the depth sounder, we crept along in the centre of the channel. The numbers gradually got larger. By the time we got to the middle of White Sound, the water was over ten feet deep.
"This is fine," Eileen said. "But how are we going to get out? Dennis and Darcy are under the impression they're coming here for a sailing vacation." Dennis is Eileen's younger brother; he and his wife Darcy were due to arrive at Green Turtle just after New Years.
The next day we were surprised to see a 120 foot mega yacht, the "Andrea Cay", inching up the channel towards the anchorage. "She's going to run aground," David predicted. But, no, she slid into White Sound with no apparent difficulties and nuzzled up to the dock at the Bluff House marina, dwarfing all the boats around her. Eileen brightened up. "If a boat that size can make it through the channel, we shouldn't have any problems escaping from here after all."
The "Andrea Cay" stayed for the New Year's eve festivities at the Bluff House and left the dock late in the afternoon on New Year's day. We were returning in our dinghy from the Junkanoo celebrations in New Plymouth just as the mega yacht was approaching the other end of the channel. "Give her a wide berth," Eileen cautioned. "No need to," David replied. "She's not moving."
Sure enough, the "Andrea Cay" had run aground; her reversing props were turning all of White Sound brown. "Not a good omen," David said. It took her about ten minutes to get off; once she was free, she eased over further into the channel and managed to exit without further ado. Dennis and Darcy arrived the next day. Over the weekend, we took them into town in the dinghy, walked around a lot, and made a couple of trips to the beach. "This is beautiful," Dennis commented. "But when are we going to go sailing?" Eileen gulped. "Maybe Monday," she said.
High tide Monday morning was at 0611. We got up before dawn and headed towards the channel at first light. Our guests were relaxed, blissfully unaware of any pending disasters (or maybe they were still half asleep). We crawled past the first set of markers, our eyes fixed on the depth sounder. The water depth dropped until there was two feet under the keel, and then began to increase. Eileen gave a sigh of relief as we glided past the last marker and entered open water. "Whew," she said. "That wasn't so bad after all."
"Thank the 'Andrea Cay'," David replied. "The channel is a foot deeper since she left."