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post #1 of Old 11-03-2003 Thread Starter
Tania Aebi
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Tidal Mysteries

When your boat is built for a large tidal range, you don't have to worry too much when the water runs out.
Last summer, I drove to the West Coast with my two sons. We traveled from Bellingham, WA, down to the Olympic Peninsula, and messed around in the area, crossing islands, bridges and tidal flats. They played with stranded fish and sea anemones in tide pools, gathered shells and oysters before the water came back in, and watched fishermen walking across the mud to pick up and reset their nets without boats. My boys observed docks lifting and dropping on the sea that poured in and out around the land we navigated, a land surrounded by boats that sat on the ground as often as they swung at anchor. It was all part of a natural cycle as regular as Old Faithful. They watched with curiousity as land contours shifted, appearing, disappearing, and appearing again. By their puzzled looks, I knew what was coming. It was inevitable that they would ask me how the tide works. My boys don't settle for quick and easy answers; they probe until every bit of information I hold has been drained, and I wasn't looking forward to them discovering that I, their circumnavigating nautical mother, know very little about tides.

The question finally came while in the company of a sailing friend that we were visiting, and as I began my answer with a few hems and haws, she jumped right in. "The moon and sun do it," she said. "They pull the ocean up and away from land and let it go again."

I could have let the explanation go at that because that's the general opinion shared by most books, including my encyclopedia, but it doesn't work for me anymore. I couldn't keep my mouth shut. "It's not that simple," I said. "If that were the case, tides would be the same everywhere, even in lakes and seas, which isn't the case at all. Tidal ranges are vastly different even in places that are geographically close to one another."

In some parts of the world, the tidal rhythms afford sailors the opportunity for an impromptu haulout.
I wasn’t trying to one-up my friend. You see, I have given this topic a good deal of thought. Up and down the East Coast alone, different areas march to different tidal rhythms with mercurial
leaps and drops in ranges within relatively small areas. How come it isn't the same everywhere? How can we explain the comparatively insignificant tide of the Caribbean, which is wide open to the Atlantic Ocean that simultaneously creates 57-foot tides in Nova Scotia's Bay of Fundy and incoming tides that can outrun a galloping horse in St. Malo, France? How come it isn't the same everywhere? Why does the current in a channel off the island of Euboea in the Mediterranean reverse itself 14 times a day in a body of water that has virtually no tide at all? It is even rumored that Aristotle drowned himself over Euboea’s tidal mystery because, apparently, life without a reason for the current wasn't a life worth living. There are more exceptions than rules when it comes to understanding tides and, while it has never made me feel suicidal, I don't know how I managed to get this far without arriving at any definitive comprehension on the phenomenon, without finding answers to all these questions, but I have.

What does one do, then, when one can't come produce a comprehensive answer which one ought to know? I can't speak for everyone, but diversions always work for me. When it concerns the kids (and most grownups, too), stories will outperform long-winded, incomplete, and dry explanations any day, and I had two tide-related tales to whip out from my sailor's lore. What I do know for sure on the subject is based on my own experiences with tide, so I told my kids and my friend the one that revealed to me for the first time just how complex tides can be.

The Panama Canal cuts through Central America, linking the Caribbean to the Pacific Ocean; only 60 miles of land and a small mountain range separate the two great bodies of water. When a boat pulls in to Panama from the Caribbean, it arrives in a tideless region. For the months, or years that vessel spent puttering about in the Caribbean, tides were never an issue, and the harbor of Colon, where vertical movement dockside is negligible, is no different. I mean, there is a small tide, but nothing worth consulting tables for or making elaborate dockline arrangements or anchor-rode calculations.

On Panama's Caribbean side, mariners don't fret about tides, but the Pacific side is an entirely different situation.

I arrived in Colon with my 26-foot boat that drew four feet, made all the preparations to transit the Canal, and, several days later, I was motoring into the Pacific Ocean. My first anchorage in the Pacific was off the island of Tobago where the water was sufficiently deep that with enough rode, my boat was fine. It wasn't until I moved to Panama City and anchored off the Balboa Yacht Club that the extent of the tide and the havoc its changes could wreak on my world became evident.

I set the anchor was set about 1,000 feet offshore, a distance determined to be sufficient because it was as far as I wanted to row in the oppressive heat with a dinghy full of provisions, and it was 20 feet deep out there. The tidal range was supposed to be about 15 feet, so I figured my boat was safe. That evening, I rowed over to another boat for dinner and it was when the rocking got so that bad dishes wouldn't stay on the table we realized something was wrong.

My boat, the boat I was on, and another boat nearby were caught in the midst of a line of rollers sweeping toward the beach. Since the land shelved so gradually out to sea, as the water receded, the ocean swell that had gently rocked us upon our high-tide arrival had stacked up in the ever-shallowing water. I had counted on somewhere between one and two feet of clearance under the hull at low tide, and I got it. What I hadn't counted on was the shelving bottom that tripped the gentle swells and turned them into nasty breakers. The three boats bucked and rolled, sinking and rising from the mud with each wave under the keel and there was nothing we could do but watch until the tide bottomed out, the flood came back in, and calm was restored. The cleanup was gross because my boat had been thoroughly dunked in the filthy bay water, and I was very shaken by how close I had come to losing her. I shudder to think what might have happened in an anchorage with a rocky bottom.

"I will always remember that awful feeling of almost losing my boat–it kept me out of tide-related trouble for the next 11 years, and then I stumbled again."
I will always remember that awful feeling, and it kept me out of tide-related trouble for 11 years, until I took a trip to Thailand and garnered my second story. We were three boats in a flotilla on our first night out from a charter base. Tired and cranky after a long day of provisioning, stowing, checking in and meeting each other, we rode a tidal current that carried us out to a cleft in a small island just as the sun was setting. Relieved over having laid some miles under the keel, the three captains consulted their separate depth sounders and set three anchors in water that was deemed sufficiently deep.

Mosquitoes droned around my head, the windless night was stifling hot, and I wasn't getting much sleep anyway, so the sound of the keel rubbing on something hard in the wee hours didn't take long to register. I was on deck in a flash and in the feeble starlight, I could see the gleaming white hull of one of the other boats lying on her side and hear muffled voices of consternation drifting across the water. The tide had receded wicked far and every time my boat swung shoreward on her anchor, we touched a coral head. I took the spare anchor and kedged us out a bit so we wouldn't swing into it anymore and cringed for what seemed like hours whenever we grazed the muddy bottom. At least we didn't end up on our side, the bottom was mostly mud and tides always come back in. By dawn, we were all safely afloat again and sailing up to visit James Bond Island, where we took great care to anchor in plenty of depth.

Low tide in the Bay of Fundy, where the tidal flux can span almost 50 feet. 

Without a major in ocean sciences, I still don't know how tides work, but the essence of all this for the average sailor is that they do exist and they are a force to be reckoned with, especially when we sail into unfamiliar territory. What I do know is that tables covering most places in the world have been calculated, tabulated, and extrapolated for the mariner, and, thanks to them, we have all the information and predictions we need to take appropriate navigational action without needing to understand the cause behind every effect. So, next time the kids ask about tides, unless I've acquired another story, I'll pull a book of tide tables out of the same sailor's store. That should turn the tide and reduce the flood of questions to a trickle, and I'll still come out looking as if I know something.

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