Course Reports

Tides, France and RYA mile building

Dolphins don’t calculate tides, fortunately they often come and see us and did so in Lyme on our trip up from Plymouth at start of November.

Quite a few Day Skippers, particularly those who have sailed only in the Med, struggle to understand just how important tides can be so here is an example I use.

We are crossing to Cherbourg from the West of the Solent so it is 60 NM which will take us about 9 hours. The tides are stronger on the French side and the asumption that one side cancels out the other really doesn’t work even on a 12 hour crossing.
At 60 miles a one degree error is a mile out at the far end. May not sound much, but let’s say you are 3 degrees out and the tide is 3 kts across the ‘Horns of Cherbourg’ plus it is wind against tide so you can only make 4.5 kts under engine or by tacking under sail. You are now only making 1.5 kts towards the hot showers and restaurant plus you are 2 hours behind target on this RYA Milebuilder.
What happens if you are wrong the other way so you are up tide. You are still 3 miles out but now close on the entrance at between 7.5 and 9 knots which equals 20 minutes to half an hour late.

Even better if you get your RYA navigation right on the Milebuilding course and we correct as we go and end up just right with plenty of time for a shower and a good meal out.

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