(AC 2162, 2581) This potentially dangerous chan should only be attempted with moderate winds (less than F4), good vis, no swell and a fair np tide. In such conditions it presents few problems. A safe passage depends on a clear understanding of tidal streams and correct timing. The Admiralty Tidal Stream Atlas for Orkney and Shetland (NP 209) gives large scale vectors and is essential. Even in ideal conditions the races off Duncansby Hd, Swilkie Pt (N end of Stroma), and Rks of Mey (Merry Men of Mey) must be avoided as they are always dangerous to small craft. Also avoid the Pentland Skerries, Muckle Skerry, Old Head, Lother Rock (S Ronaldsay), and Dunnet Hd on E-going flood. For passages across the Firth see CCC SDs for Orkney.
At E end the Firth is entered between Duncansby Hd and Old Hd (S Ronaldsay), between which lie Muckle Skerry and the Pentland Skerries. Near the centre of Firth are the Islands of Swona (N side) and Stroma (S side). Outer Sound (main chan, 2.5M wide) runs between Swona and Stroma; Inner Sound (1•5M wide) between Stroma and the mainland. Rks of Mey extend about 2ca N of St John’s Pt. The W end of the Firth is between Dunnet Hd and Tor Ness (Hoy).
Tide flows strongly around and through the Orkney Islands. The Pentland Firth is a dangerous area for all craft, tidal flows reach 12 knots between Duncansby Head and S Ronaldsay. W of Dunnet Hd and Hoy is less violent. There is little tide within Scapa Flow. Tidal streams reach 8-9kn at sp in the Outer Sound, and 9-12kn between Pentland Skerries and Duncansby Hd. The resultant dangerous seas, very strong eddies and violent races should be avoided by yachts at all costs.
The E-going stream begins at HW Aberdeen + 0500, and the W-going at HW Aberdeen – 0105. Duncansby Race extends ENE towards Muckle Skerry on the SE-going stream, but by HW Aberdeen – 0440 it extends NW from Duncansby Hd. Note: HW at Muckle Skerry is the same time as HW Dover. A persistent race off Swilkie Pt, at N end of Stroma, is very dangerous with a strong W’ly wind over a W-going stream. The most dangerous and extensive race in the Firth is Merry Men of Mey. It forms off St John’s Pt on W-going stream at HW Aberdeen – 0150 and for a while extends right across to Tor Ness with heavy breaking seas even in fine weather.
Passage Westward: This is the more difficult direction due to prevailing W winds. Freswick B, 3•5M S of Duncansby Hd, is a good waiting anch; here an eddy runs N for 9 hrs. Round Duncansby Hd close in at HW Aberdeen –0220, as the ebb starts to run W. Take a mid-course through the Inner Sound to appr the Rks of Mey from close inshore. Gills Bay is a temp anch if early; do not pass Rks of Mey until ebb has run for at least 2 hrs. Pass 100m N of the Rks (awash).
Passage Eastward: With a fair wind and tide, no race forms and the passage is easier. Leave Scrabster at local LW+1 so as to be close off Dunnet Hd not before HW Aberdeen +0340 when the E-going flood starts to make. If late, give the Hd a wide berth. Having rounded the Rks of Mey, steer S initially to avoid being set onto the rky S tip of Stroma, marked by unlit SCM bn. Then keep mid-chan through the Inner Sound and maintain this offing to give Duncansby Hd a wide berth.