Tide and Current

Tide is the vertical motion of the water caused mainly by the gravitational effects of the sun and the moon. When there is no vertical motion this is referred to as stand. Current, or more correctly, tidal stream is the horizontal flow of the water. The current coming in from the sea is called a flood current while the current flowing out to sea is the ebb current. When there is no horizontal movement this is referred to as slack, slack water or the turn.

“Commonly used expressions like “flood tide” and “ebb tide” should be avoided, as they confuse the horizontal motions of tidal currents with the vertical displacements of the tide” Oceanography of the British Columbia Coast – Richard E Thomson Published by Department of Fisheries and Oceans.

By using the Tide and Current Tables correctly you will be able to predict the depth at low and high water and be able to use the current to your advantage.

One question many boaters ask is how are the Tables arranged? One of the commercial books is arranged in alphabetical order while the Official Tables produced by the Canadian Hydrographic Service are arranged in order from seaward. They start at the western entrance of Juan de Fuca Strait, go down into Puget Sound and then northwards through the Strait of Georgia.

A Reference Port is where the Tidal height has been measured such as Fulford Harbour which is the Reference Port of the Southern Gulf Islands. There are tables of corrections to the Secondary Ports. A Reference Station gives the details of the currents and similarly there are tables of corrections to the Secondary Stations.

It is critical to understand that the time of low water stand and the time of the turn to flood do not normally occur at the same time. In the Sidney area, the difference of the time of low water stand and the turn to flood in Sidney Channel can be 1 hour and 40 minutes or greater.  Likewise the time of high water stand and the turn to ebb do not correspond.

ABOUT THE AUTHOR: Bruce Stott, co-founder of Gulf Islands Cruising School Ltd. has been a Canadian Yachting Association certified instructor since 1971.  He has taught aboard both sail and power boats ranging in size from 8' to 86' and is author of Home Study Coastal Navigation Course

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