Mariners encounter all sorts of unusual winds and currents, but polar explorer Fridtjof Nansen was baffled in August 1893 when an invisible force seemed to hold back his ship Fram. Four hours steaming though the “dead water” produced less progress than Nansen would expect from just half an hour’s rowing.
“We could hardly get on at all for the dead water,” wrote Nansen. “We made loops in our course… tried all sorts of antics to get clear of it, but to very little purpose.”
Dead water had been known for centuries, but Nansen was the first to describe it scientifically. In particular, he noted that while the water at the surface was fresh enough to drink, underneath the hull it was thoroughly salty.
Dead water occurs when a layer of fresh water, for example from a melted glacier, lies over denser salt water. The ship’s movement sets up waves, called interfacial waves, between the two layers of liquid. These waves absorb the energy of the ship and set up currents which make it difficult to move or steer.
The effect is worse for vessels which cannot move much faster than the speed of the waves, around three knots. Modern ships, being generally much speedier, are no longer held back by mysterious stretches of dead water.