Tides and Sea Conditions
Large ocean undulations, generated by distant storms and unrelated to local causes, are called swells. The surface of a swell may be perfectly calm, but it is usually textured by the wind into groups of tiny ripples called "catspaws". The ripples gradually build into waves.
As the waves travel quickly over a long fetch, the distance free of obstructions, each crest reaches higher above its trough. Increasing wind tears at the wave tops, revealing whitecaps and throwing off spume. When this heavy sea encounters shallow water, its energy can no longer be absorbed by the circular movement of water within each wave. The crests rise and break. Surf crashes ashore.
The same sea, meeting a current, will rear up, creating a rip, sometimes amplified by the narrowing funnel of an inlet. Over long fetches of shallow water, strong winds may create waves of moderate height, but with a viciously steep and short chop- which is even more dangerous than ocean waves of greater size. Lake Erie and Delaware Bay, for example, are two bodies of water renowned for choppy conditions.
Both coastal and inland boaters are familiar with currents, the horizontal flow of water in a downstream direction. Currents are also found in open water where they range from huge, persistent ocean movements, such as the Gulf Stream or the California Current, to the strong but short-lived undertow, or rip current, of a beach where surf finds its way back offshore.
Ocean, lake and river currents respond to the push of prevailing winds. In addition, ocean currents are affected by variations in water density resulting from different levels of salinity and temperatures.
The largest currents are part of the world’s five gyres- giant circular oceanic currents. There are two gyres in the Northern Hemisphere that travels in a clockwise
direction: one circling the North Atlantic; the other, the North Pacific. Three gyres in the Southern Hemisphere circle the South Atlantic, the South Pacific and the Indian Ocean in a counterclockwise direction. While the gyres are surface currents, there are other equally important countervailing deep currents.
Regular, intermittent currents that respond to movement of the sun and moon are called tidal currents. Tides are the actual rise and fall in local water level as tidal currents force masses of water alternately against and away from shore. Incoming tidal currents flood, then ebb as they retreat.The strongest are associated with spring tides during new and full moons, when the moon and sun pull in parallel directions. Tide currents flow more gently as neap tides that occur at the quarter moon.
Every current, regardless of its origin, has a set and a drift (speed). Set is the true direction toward which a current flows; drift is its speed. The speed of tidal currents and the height of the tides are so important to coastal navigation that annual tide tables and tidal current tables are published under government supervision
Depending upon the bodies of water on which you boat, tides can have a major impact on your boating experience. Watch the tide charts or listen to tide reports in your area before you go boating. Going aground is never a good time.
To find more information on tides and currents that affect your area, you may look in a local tide table. Tide tables offer a broad range of information about tides, including when high and low tides will occur, and what the high and low tides will be at a given location. You may also see current information such as the speed of the current and when the current changes direction.
While tide tables offer the most information about tides, you may also find tide information in your local paper, on the weather reports, or on the VHF weather stations. Below are sample tide and current tables. To find tide information in your area, you may go to the following site http://www.boatus.com/news/mweather.htm