Is the Irish Sea the Roughest in the World? No.

The Irish Sea can be choppy, especially in winter, but it's far from the planet's roughest waters. That distinction belongs to regions where unimpeded winds and currents meet:

• Drake Passage (South America–Antarctica) – "The world's most violent stretch of water."
• Cape of Good Hope (South Africa) – Roaring Forties, Agulhas Current clashes.
• Beagle Channel / Cape Horn – Extreme winds, waves, and williwaws.
• Southern Ocean (generally) – Unbroken fetch generates massive swells.

The Irish Sea's semi-enclosed geography limits fetch and swell development. It's rough for a marginal sea, but globally, it's moderate.