Why Ships Suddenly Stop in Calm Water — Dead Water

In 1893, Nansen's ship Fram was steaming through perfectly calm Arctic water when it suddenly slowed to a crawl. The engine was at full power, but something invisible was holding her back. Sailors called it "dead water". The cause is hidden beneath the surface: a layer of fresh water lying on top of heavier salt water. A moving ship makes waves on that invisible boundary, and those internal waves steal its speed. We look at Ekman's 1904 experiment that solved the mystery, the 2020 discovery that dead water comes in two kinds, and whether it may have helped decide the Battle of Actium.