![]() ![]() Difficult channels are also more safely navigated during slack water, as any flow may set a vessel out of a channel into danger.Ĭombined tidal stream and current In areas with potentially dangerous tides and currents, it is standard practice for divers to plan a dive at slack times.įor any vessel, a favourable flow will improve the vessel's speed over the bottom for a given speed in the water. Following low tide, visibility can be reduced as the ebb draws silt, mud, and other particulates with it. Slack water following high tide can improve underwater visibility, as the previously incoming tide brings clear water with it. Implications for seafarers įor scuba divers, the absence of a flow means that less effort is required to swim and there is less likelihood of drifting away from a vessel or shore. ![]() Since the level of the basin is always at mean sea level, the flood in the mouth starts at half tide, and its velocity is at its greatest at the time of high water, with the strongest ebb occurring conversely at low water. In 1884, Thornton Lecky illustrated the phenomenon with an inland basin of infinite size, connected to the sea by a narrow mouth. Similarly, the flood may run for up to three hours after the water has started to fall. The time of slack water, particularly in constricted waters, does not occur at high and low water, and in certain areas, such as Primera Angostura, the ebb may run for up to three hours after the water level has started to rise. Slack water can be estimated using a tidal atlas or the tidal diamond information on a nautical chart. It occurs before the direction of the tidal stream reverses. Slack water is a short period in a body of tidal water when the water is completely unstressed, and there is no movement either way in the tidal stream.
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