Slack water
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Slack water, or slack tide, is the time during which no appreciable tidal current is flowing in a body of water.
Slack water usually occurs near high water and low water, and are occasions in between when the direction of the flow reverses.[1] Commonly available tide tables indicate the time of high and low water at popular locations, such as ports, but not at every specific area of that a navigator may be. Slack water can be accurately calculated in most regions using a tide table or current table combined with either a tidal atlas or the tidal diamond information on a nautical chart.[2]
Slack water is of particular interest to sailors and scuba divers.
For divers, the absence of a current means that less effort is required to swim to and remain at a given site, and there is less likelihood of drifting away from the boat providing surface cover. Slack water can reduce visibility, as there is no current to remove debris, such as sand or mud, which the diver kicks up at the dive site. Except when drift diving, it is standard practice for divers to plan to dive at slack water.
For sail boats with limited top speeds, a favorable current can substantially improve the vessel's speed in the water. Difficult channels are also more safely navigated during slack water, as current may set a vessel out of a channel and into dangerous shoal water.
[edit] References
- ^ http://eezway.org/clinic/Oceanography/Resources/Tides.pdf The American Practical Navigator, page 139
- ^ Sport Diving, British Sub Aqua Club, ISBN0091638313, page 167
