This is the passage to the west of Brest, between the mainland and Ouessant.
For anyone travelling to Southern Brittany, this page may be useful, however, please refer to the Featherstone West France Cruising Companion (2nd edition) for more detailed information, especially if travelling by yacht.
Having studied the various tidal atlases and personal experience, the slack water for the passages appear to be as follows:
Chanel du Four
HW Brest +5 (for 30 mins)
HW Brest -1 (for 10 mins)
Raz de Sein
HW Brest +4 (for 30 min)
HW Brest -2 (for 10 min)
Chenal du Four – High water Brest to HW +30mins and High water Brest +5.5 hours
Do check the books and almanac and ask other mariners, as the information appears to differ. Also the books often refer to the best tide for a yacht which enters the channel from the north or south and wishes to do the whole passage.
As well as the waves and tides, there are often fog banks caused by the meeting of the currents
Raz de Sein – You need to check the tide tables to see when the slack water as the times often quoted in the books of HW-1 and HW+5.5 does not seem to be accurate.
Do have a look at our 2017 video of travelling through the Raz – www.youtube.com/watch?v=l7m6Vs…
Amazing Webcam – audierne.info/webcamsgaleries/…