Dear faldage,

High Tides along the south coast of the UK:

This is all strictly non-technical and whether it will assist you in universal understanding I hesitate to predict! I don't think it helped me much - knowledge is one thing, understanding another.

What I am told and what I read do not seem to agree. An amateur yachtsman has assured me, I think mistakenly, that the high tide along the south coast moves from west to east. The Atlantic high tide he tells me swells back around both sides of Ireland and around the north of Scotland, moving up the channel and down the North Sea (would this form a sort of mælstrom where they meet, I wonder?). When I look at tide tables for south coast ports, however, my interpretation is that the tide moves east to west along the Channel coast. I think I prefer to trust the tide tables and to avoid cruising on my friend’s yacht!

It seems from the tables that there is a high tide approximately every 12 hours 20 minutes. The double tide effect at Poole Harbour causes a secondary peak that occurs about 4 hours after the main high tide. I don't know why it occurs, perhaps Bean can explain; it is generally lower than the main peak, but there appears to be variation in this, I guess depending on where you are in the spring/neap tide cycle. A similar effect is seen at Southampton due I believe to the Isle of Wight and the two arms of the Solent, but there the two peaks are mostly about the same height with a drop of only a few inches between them, so this has the effect of lengthening the duration of high water – obviously very desirable for a port. Again this effect seems more or less marked depending, I guess, on the spring/neap cycle.

Where I have given conclusions rather than facts above they are based on my deductions arrived at from looking at the tide tables so could well be completely erroneous!

Two interesting links:

http://www.ukho.gov.uk/easytide.html
http://www.alia.ie/sailing/tides.html

dxb