Tidal waters

Our passage between Craignure and Oban takes us past the very South
end of Lismore Island with its lighthouse and Lady Rock a distance of
about ¼ mile or less. The tidal range, that is the difference in
height between high and low water, isn't that great around here, it is
about 3 metres at the moment being spring tides and it goes down to
about a metre at neaps.
Despite the small range of tide the mainland and islands around this
part of the world cause this flow of water to be crammed into narrow
sounds and firths. This results in strong tidal currents, the most
famous around these parts being Corryvreckan which has its whirlpools
due to the nature of the seabed and the very strong tidal flow between
the islands at that point.
The waters around Lismore also have strong currents which we have to
take into account when steering our course to pass safely between the
Island and the rocks. I hope that you can see from the attached photo
of our GPS plotter two arrows, the blue shows the way the ship is
pointing and the red shows the actual course being made over the
ground. As you can see if you don't keep a good eye on the way the
ship is moving through the water then you would easily be swept up
onto the rocks. The strange thing is that at you approach the gap the
direction of the current goes right round so initially you are
steering one way to counteract the current then the other. As the
current hits the bow it actually makes the ship roll and swerve off
suddenly, not bad considering we weigh about 2,500 tons.