Tides and currents — predictions and corrections

Bowditch Ch. 24 §2401

Bowditch Ch. 24 §2401 — Currents Surface ocean currents are driven primarily by wind, with major gyres in each ocean basin. Tidal currents are driven by tide rather than wind and reverse direction with the tide.

Bowditch Ch. 24 §2402

Bowditch Ch. 24 §2402 — Currents The vector triangle for current correction is: course steered + drift vector = course made good. Inverting it: from course made good and drift, derive the course steered required to make a given track over ground.

Bowditch Ch. 9 §901

Bowditch Ch. 9 §901 — Tides and Tidal Currents Tides are the periodic vertical rise and fall of the sea level due to the gravitational interaction of the moon, sun, and earth. The principal lunar tide has a period of approximately 12 hours 25 minutes.

Bowditch Ch. 9 §902

Bowditch Ch. 9 §902 — Tides and Tidal Currents Spring tides occur near new and full moon and have the greatest range. Neap tides occur near first and last quarter moon and have the smallest range.

Bowditch Ch. 9 §903

Bowditch Ch. 9 §903 — Tides and Tidal Currents Tidal currents are the horizontal flow of water associated with the rise and fall of the tide. Flood is incoming, ebb is outgoing, slack water is the brief period of zero flow at the turn.

Bowditch Ch. 9 §904

Bowditch Ch. 9 §904 — Tides and Tidal Currents Charted soundings on US charts are referenced to Mean Lower Low Water (MLLW), the datum from which the tide tables predict the height of tide. Actual depth of water equals the charted sounding plus the predicted height of tide, and underkeel clearance equals that actual depth minus the vessel's draft. Heights of features such as bridges and lights are referenced instead to Mean High Water, so vertical clearance shrinks as the tide rises.