Orkney Islands

Orkney lies off the northern tip of Scotland, separated from the mainland by the Pentland Firth — one of the most powerful tidal races anywhere in the world. Spring streams in the Firth reach 16 knots, generating standing waves and overfalls that remain a serious hazard to small craft. The archipelago's spring tidal range is moderate by UK standards — around 3.5 metres at Kirkwall — but the volume of water forced through the narrow sounds between islands drives currents of 2 to 4 knots through most inter-island passages. Scapa Flow, the huge natural anchorage at the centre of the archipelago, is sheltered enough to be navigable in almost any conditions; it served as the British Grand Fleet's base in both World Wars and holds the wrecks of the scuttled German High Seas Fleet, making it one of the world's premier wreck-diving destinations. Stromness on the west mainland faces south into Scapa Flow with Hoy Sound running to its west at 3 to 4 knots on springs. The Old Man of Hoy sea stack rises 137 metres from the Atlantic cliffs of Hoy. Viking heritage is everywhere — the islands were Norwegian until 1468. Tidal streams on the north coast of the mainland flood northward through Hoy Sound and reverse on the ebb.