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Pentland Firth - Tides
PENTLAND FIRTH TIDES Tide Predictions From UK Admiralty
Between Holborn and
Between Rough Head and Dunnet Head there is an almost continuous N and NE-going eddy which increases the size of the waves off Briga Head (1 mile SW of Dunnet Head). When a NW swell persists the sea up to 5 cables off Dunnet head becomes confused and strong offshore NW sets can be experienced.
Dunnet Bay itself can experience very heavy seas rolling into the bay during W and NW gales.
South-west coast of
Hoy Off Rora Head
The E-going stream W of Hoy divides off Rora Head and sets SE towards Tor Ness and quickly increases in strength as the ness is approached, and NE towards Kame of Hoy. The W-going stream W of Hoy is, similarly, the combination, W of Rora Head, of the SW-going coastal stream from the vicinity of Kame of Hoy and the NW-going coastal stream, emanating from Pentland Firth, which rapidly loses strength with the distance from Tor Ness.
The E approach to the firth is divided into 2 channels by Pentland Skerries, an extensive group of islets and rocks lying nearly midway between Duncansby Head (mainland) and Old Head (Orkney).
Stroma and Swona,
Routes through Pentland Firth
Tidal Information for Pentland Firth
Tidal streams run with great strength and rates of up to 16kts have been reported close W of Pentland Skerries.
Pentland Firth West
In mid-channel about 3 ½ miles N of Dunnet Head the E-going stream begins at (-0450 HW Dover). The initial direction is SE but changes anti-clockwise, spring rate increasing rapidly from ½ kt; this stream has a mean direction of 105° and is at full strength with a spring rate 3 ½ kts, between (-0350 HW Dover) and (+0010 HW Dover). At the end of this period the stream begins to change direction anti-clockwise and rapidly loses strength. The W-going stream begins at (+0210 HW Dover) with a mean direction 280° and a spring rate of 3 ¼ kts. Further E, about 3 miles N of St John's Point, the E-going stream begins at (-0450 HW Dover) and the W-going stream at (+0120 HW Dover) with a spring rate of 7 kts in both directions.
Towards the N side of the firth, off Tor Ness, the E-going tidal stream begins at (-0530 HW Dover) and the W-going stream begins at (+0030 HW Dover) with rates of 6 to 7 kts. The E-going stream is diffused E of Tor Ness and runs towards the N and S of Swona.
race: Merry men of Mey
The race forms off the Men of Mey rocks and initially extends W towards Dunnet Head, but as the W-going stream increases in strength the race begins to extend from the bank 1½ miles NW off St John's Point in a NNW direction. When the W-going tidal stream has attained its full strength heavy breaking seas extend the whole way across the firth between St John's Point and Tor ness even in fine weather.
At (+0535 HW Dover) the SE end of the race becomes detached from the Men of Mey Rocks leaving a clear passage, which gradually widens N, between the rocks and the breaking seas. In other areas' the race persists.
At (-0530 HW Dover) the NW end of the race off Tor Ness begins to subside.
The race subsides in mid-channel at the onset of the E-going tidal stream.
Eddies and races
adjacent to Stroma
During the E-going streams through the Outer and Inner Sounds an eddy forms off the E side of Stroma and gradually extends about 1 mile E of the island, this eddy causes a N-going stream along the E side of Stroma.
A corresponding eddy forms off the W side of Stroma during the W-going streams through the sounds and gradually extends about 2 ½ miles WNW from the island and causes a N-going stream along the W side of Stroma.
Eddies and races adjacent to
During the E-going and W-going tidal streams races will form, respectively SE and SW of the Tails of The Tarf on the edge of eddies E and W of Swona; where they may become violent when wind is opposed to the tidal stream.
In the Inner Sound the main tidal streams run in mid-channel, the E-going stream begins at (-0530 HW Dover) and the W-going stream at (+0030 HW Dover) at a rate of about 5 kts in both directions. Eddies in general are weak and reach a maximum rate of 1 kt.
During the E-going tidal stream a race which can be particularly violent during E and SE gales, forms off Ness of Huna.
Channel between Duncansby
and Pentland Skerries
At (-0220 HW Dover) the race extends NW from the Ness of Duncansby and gives rise to the Boars of Duncansby, 1 mile NW of the ness. 3 hours later the race begins to subside.
At (+0115 HW Dover) the race ceases temporarily, coincident with commencement of the NW-going stream and re-forms at (+0505 HW Dover) off the Ness of Duncansby extending ENE. At (-0535 HW Dover) the race ceases again temporarily.
Duncansby Race is extremely violent and dangerous when a SE-going stream is opposed by E and SE gales and when the NW-going stream is opposed to W gales.
between South Ronaldsay and Muckle Skerry
At (-0600 HW Dover) the E-going stream begins with a spring rate of about 8 kts. As the stream gains strength the Liddel Eddy forms, initially SE of Old head.
At (-0350 HW Dover) the Liddel eddy gives rise to an S-going stream along the SE side of South Ronaldsay and as it's strength increases and the strength of the E-going stream S of Old Head starts to decrease, it forces its way S and W past Old Head towards Muckle Skerry and along the S coast of South Ronaldsay. A race starts to form off Old Head and persists until about (-0220 HW Dover).
At (-0320 HW Dover) the Liddel eddy is W-going and becomes firmly established along the S coast of South Ronaldsay gradually extending S from the coast. Farther offshore the E-going stream persists but with less strength.
About (-0220 HW Dover) the Liddel Eddy is W-going and occupies the N half of the passage, the E-going stream still persists in the S half. Heavy overfalls and breakers will occur along the boundary between the eddy and the stream.
At about (-0020 HW Dover) the Liddel Eddy is W-going and extends the whole way across the passage except for what remains of the E-going stream close N of Muckle Skerry.
At (-0220 HW Dover) the true W-going stream begins throughout the passage and the race off Old Head subsides.
During the E-going tidal stream, the SE-going main tidal stream between Swona and South Ronaldsay joins the main tidal stream S of Lothar Rock.
Lothar Eddy and Race
At, (+0100 to -0600 HW Dover) during the NW and W-going tidal streams, respectively SW and N of Muckle Skerry, an eddy forms along the S side of the channel between Muckle Skerry.
Tidal streams 4 miles ESE of the skerries are affected by the eddies described above; they rotate clockwise and are relatively weak.