I recently visited Normandy,France with their very high tides. in every shore there are updated tide tables, however the provided data is time and [B]coefficient [/B]rather than water height in meters. ( see attached picture of such sign)
I was not able to find an explanation or figure it out.
Any explanation or pointer to literature will be greatly appreciated.
Here’s what I found after a google search, from sailingalmanac.com " Tidal coefficients is systems primarily used in France and therefore in many French pilot books, web sites and harbor notices. Its a tabular system that depicts the ‘size’ or ‘magnitude’ of the expected tide at a simple glance. It eliminates the need of having to look up and calculate the range of tides and the need to determine whether its neaps or springs or anywhere in between. The coefficients usuall.y range from anywhere between 20 and 120 and a good typical guide to use is:
20- very small neap
45-mean neap
70-average tide
95-mean spring
120-very big spring"
The French Atlantic coast has a rather erratic tidal system. From the flat Channel coast to the rocky and indented Normandy and Brittany coasts (both concerned by the Atlantic tide and the North Sea ‘back-tide’), to the flat southwestern coast. Therefore, long time ago, they opted for this system.
I could not find an English description, but briefly:
The coefficient of each tide is its normalized range calculated for Brest, 20 is the minimum possible and 120 is the maximum possible range. The times at Brest are calculated too.
Each small port or marina has a stable offset for the time of high/low water and a factor for the tidal range (the coefficient). Coming from the sea, with the values for Brest and the local corrections on board, it is easy to calculate the best arrival time for any small place.
The greater ports have their own precalculated tide tables.
Nevertheless, this coefficient seems to be a hereditary knowledge for all coastal inhabitants. The maritime part looks for the low water and the onshore part for the high water. A high coefficient combined with a deep depression and a strong storm into the Channel mouth means no good for the coastal regions.
Thanks for the info.
So…the coefficient means " small tide" , “big tide” , " ohhh sh@#@2" .
not really a measurable quantity by which to plan a passage on shallow waters…
Good enough for me, as I am not sailing there anyway.
Thanks