In reality, tides are influenced by geological differences in the shape of the globe itself and the unique characteristics of the ocean floor and coastline dynamics. The fundamental dynamics of tides are explained in an ideal world with no variables. Each period of tides, therefore is six hours, 12.5 minutes each. That means that tidal changes (slack high and slack low) occur on a 24 hour, 50 minute cycle. The catch is that it's based on a "lunar" day which is fifty minutes longer than a "solar" or sun day, our normal 24-hour rotation. This tidal range typically changes twice a day. Those gravitational forces create water movement called "tides" and they vary from high to low – the "tidal range" – that determine the depth of water in any one spot throughout the day. Those affects are most noticeable along ocean shorelines around the world. This means that the moon's gravitational forces on earth are twice that of the sun. While the sun has 27 million times the mass of the moon, it is 390 times farther away from earth. When the moon is at right angles to the line between the earth and the sun, a "neap" is formed. When the moon and the sun are aligned with the earth, the affect is called a "spring" tide. Considering the earth as a perfect sphere and the oceans as a mass of fluid surrounding it, that mass of water is pulled by gravity depending on the position of the moon and the sun. Following is a primer on basic tidal dynamics and how this info’ can help one use this water movement info to safely and knowledgeably paddle our ocean waters.īasically, tides are caused by the gravitational affects of the moon and sun on the water masses of the earth. Knowing what causes tides and their dynamics is key to safely paddling ocean byways and using tide information to aid in navigation. In North America tides fluctuate greatly, from extremes in Alaska in the west and Nova Scotia in the east (45' difference in the Bay of Fundy, for example) to barely noticeable differences out to sea. Tides are an everyday occurrence along all coastal areas. In both cases, attention had not been paid to the affects tides have on our ocean waterways. Darkness and dropping temperatures made their situation life threatening. Just recently a newspaper carried a story about two kayakers out east who were rescued from the mud flats of a bay where the outgoing tide left them in the middle of peanut buttery mud over 200 yards from shore. We returned several hours later to see our boats lying on shore like basking sea lions – a good 50 yards from the water! We took our bowlines and tied off on a spike of sand-polished, gray wood sticking out of the sand. We entered a bay in our kayaks and sought out a gradually-sloped sandy section of beach with a few clumps of driftwood scattered throughout the area. My first encounter with tides came one afternoon in Alaska.
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