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tide charts: approximate or exact?

I've been having a debate with one of my crewmates about the local tides. We're out sailing on Narragansett Bay seven days a week. I've been noticing that the info on the tide chart we have is always seems to be off by more than a few minutes. Are tide chartes approximations or do they supposedly have this down to an exact science?
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they are approximate, one thing that comes to mind is wind or storms can change the hight and times of tides, as in New York harbor any east wind slows the ebb and increases the hight.
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Tide charts are fairly accurate, but will not be exact, unless you're at the spot they're calculated for. The further you get from a tide station, the spots where the depths are calculated fairly precisely, the less accurate it will be.

Also, geography and terrestrial features, like points and necks will change the timing of the tides slightly. They're not meant to give you to the minute data for every location, but an approximate idea of what the tide will be doing at roughly what time.

Weather can also affect the effective height of tides... a constant west wind will cause water to "pile" up on the eastern side of a bay....

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post #4 of 5 Old 10-01-2008
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Quote:
Originally Posted by sailingdog View Post
Tide charts are fairly accurate, but will not be exact, unless you're at the spot they're calculated for. The further you get from a tide station, the spots where the depths are calculated fairly precisely, the less accurate it will be.

Also, geography and terrestrial features, like points and necks will change the timing of the tides slightly. They're not meant to give you to the minute data for every location, but an approximate idea of what the tide will be doing at roughly what time.

Weather can also affect the effective height of tides... a constant west wind will cause water to "pile" up on the eastern side of a bay....
What SD said is pretty close to reality. But Include storm surges, heavy rains in the mountains and other minor details that affect the tides and currents. Yah! add Daylight Savings to it also...this could be why you may be an hour off.

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post #5 of 5 Old 10-01-2008
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On the upper Chesapeake, a strong wind (particularly from the North or South) can completely negate the tide. A winter gale from the North will hold the "tide" out when it should be coming in according to the tables. It's wind-driven rather than gravity induced tide.


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