ASA 105: Skill 8, Tide and Current

 


8.Use the tide and current tables to find:

  • Times and heights of tides at reference and secondary ports.
  • Direction and rate of current at referenced and secondary stations.
Tide is the vertical movement of water.  Current is the horizontal movement of water.  The two are related.  On the US East Coast the tidal cycle is diurnal with high tides occurring about every 12 1/2 to13 hours.  Refer to Eldridge 2022 Newport pages and note that high or low tides are a little later every day.  The tidal range varies as well.  Time of high or low water and tidal range are not the same everywhere.  Refer to the Boston pages, for example, to see that the time of high water is three hours later than at Newport and the range is 9.5 ft.

Boston and Newport are among the list of primary tidal stations.  Secondary stations are noted separately on pages 12 through 20.  Page 15 shows the time of high water at secondary stations located on chart 1210 Tr.

There are various publications showing current vectors for speed and direction at any given time of day and for every day of the year.  Intermediate points are related back to a standard reference point.  Paradise Cay Publications, www.paraccay.com, publish tide and current tables for many coasts.  Some electronic navigation suites have such information displayed.

In New England we use Eldridge Tide and Pilot most often.  The format and utility are very convenient to our sailing (and 105 test) area.  It contains tide tables and useful information for navigators.

Looking at Eldridge Tide and Pilot 2022:
    Reference Port: Newport RI, tides are shown for each day of the year on pages 84 through 89
    Secondary Port: For example, Block Island, Old Harbor, on page 15
    Current chart for Narragansett Bay based on reference port Newport is on page 90


Eldridge 2022 page 204 describes the rule of 12ths for adjusting tide heights for any time of day.


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