Wow Alan, that sounds really spectacular, thanks.
I remember a few years ago standing on the North mainland of Orkney and looking out onto Eynhallow Sound which is between Orkney mainland and the island of Rousay. In the midle of the sound, which is about 1 mile across, is a small island called Eynhallow (hence the name of the sound). I could see a large standing wave tumbling onto itself rather fiercely. As the tide overcame the current (or vice versa) the wave bowed out and after a while the bow was broken and the current rushed through. It looked VERY frightening.
When I lived on Orkney (believe it or not I was a policeman up there - the polis as we were known) a small rowing boat with two persons on board was crossing the sound and was capsised. The bodies were never found. Well, the remains of one (minus head) was washed up months later somewhere by John O'Groats. I was told that the boat was sucked down in a whirlpool!
I have also flown over the Pentland Firth many times and have looked down is astonishment at the 'boiling' waters and whirlpools. I did cross in a force 8 gale once in the short sea route ferry from John O'Groats, which in those days was an old 40 foot boat. The hatches were battened down and a 45 minuite journey took 2.5 hours. In the same storm a fishing boat went down North of Orkney and 5 persons were drowned (and still I wanted a boat of my own).
All this and they have CLOSED the Coastguard post on Orkney!
Does anyone know these stretches of water and what they are like to sail in a rib?