One of the reasons for the establishment of a lighthouse is to mark the dangers from the effect of extreme tides (low and high) on surrounding lands, islands, waterways, and beaches.
Look at the photo on the left of my old lighthouse at McInnes Island at low tide (click for a larger version). We can tell it is low tide because the kelp is exposed on the rocks, and the high tide mark on the rocks is marked by a dirty black line. Here on the Pacific Coast of Canada, the tides come in and go out twice a day, and the range is between seventeen (17) and twenty-one (21) feet (6 to 7 meters)!
Note the small rock at dead center, bottom of the photo. At high tide that would be covered and become a menace to navigation. In this case this is not a marked shipping channel so no marker is necessary. The reason for the lighthouse (visible on the left of the large island) is that it was listed as a landfall light. A marker for ships coming in from the Pacific Ocean to the British Columbia coastline, and also a marker for the entrance to Milbanke Sound. It really doesn’t mark the island as dangerous; just an indicator of a mariner’s location on the ocean.
To return to a docked boat on the BC coast after a few hours of sightseeing or shopping is sometimes a surprise for many tourists. The docks for the boats are built to float up and down on fixed pilings to accommodate the 21 foot tides (see photo left). To get onto the dock you walk up or down a ramp. A roller on the lower end rolls along the dock as the tide rises or falls. The top part of the ramp is hinged.
The tides change approximately every six hours, so if you left your boat and walked up the steep ramp to the topside dock at 10 AM (low tide) and came back at 2 PM (4 hours difference), the ramp would be almost horizontal (high tide). If you had lots of heavy groceries to move it was always a good idea to plan at what time of day you wanted to move them! Continue reading