The classic anchor shape on a sailor’s tattoo caused almost as many problems as it solved. This episode explains how anchors really work, starting with the myth that weight alone holds a ship. Bronze Age stone anchors, Maori stones for waka, and Greek baskets of stones or lead filled logs relied on mass and friction, but water’s buoyancy makes a rock lighter and a storm’s pull too strong for any liftable weight. The shift to hooking came early: iron flukes on anchors from the Roman Nemi ships built for Caligula, and a 10th century iron anchor with a perpendicular wooden stock from the Ladby ship burial in Denmark, a crossbar that forces the flukes to turn down into the seabed.

The real key is scope, the ratio of rode to depth, at least four to one in calm weather and up to ten to one in a storm, so the pull stays horizontal. Heavy chain sags into a catenary curve that absorbs gusts as the ship must lift it off the bottom. From there the episode follows the design race: the fouling prone Admiralty pattern, the stockless anchor of around 1821 that stows in a hawsepipe but rolls out of the mud, the CQR plow, the Danforth, and modern roll bar scoop anchors such as the Rocna, Spade, and Mantis.

• Mathematician Geoffrey Ingram Taylor invented the CQR plow anchor in 1933, which can plow a furrow and pop out under extreme loads.
• Richard Danforth’s 1940s anchor for landing craft can kite across the bottom like a wing in strong current.
• A roll bar makes it impossible for a scoop anchor to rest upside down, tipping its sharp toe into the mud.
• Robert Stevenson’s 1807 mushroom anchor for the Bell Rock lighthouse light vessel buries itself in silt and can hold up to ten times its weight.
• In kedging, crews rowed a kedge anchor ahead and hauled a becalmed warship to it by marching around the capstan.