Celtic Sea

These waters cover the Atlantic shelf south of Ireland and west of Wales, Cornwall, Devon and Brittany. They connect the Saint George's Channel, Bristol Channel and English Channel with the deeper Atlantic and the approaches to Biscay. The Isles of Scilly lie within this open sea as a low cluster of islands. Atlantic swells meet the rising sea floor here, while separate wave systems arrive from the adjacent channels. The result is short, confused water in gales and heavy surf along exposed coasts. Shoals and islands provide a few landmarks, but the western edge offers little shelter from deep-ocean weather.

Fishing and coastal shipping long crossed these waters between the British Isles and Brittany. Ships bound for Atlantic ports used the channels on either side, where tides, headlands and changing winds determined progress. Shoals such as the Scillies and Fastnet were both landmarks and hazards, while storms could scatter fleets beyond sight of land. Local pilots and knowledge of tides helped sailors cross the exposed approaches.