Uncommon Carriers

by John McPhee

Today the Port Revel merchant marine is going to practice meeting and overtaking in the Suez Canal. This is a replica of the southernmost four miles of Suez, and its bottom and bank effects are quite enough for one ship, let alone two. The bow wave, humping up between the bow and the bank, creates a bow cushion that tends to push the bow away if the ship runs too close to one side. Pumping water out from under the stern, the propeller lowers the pressure there. Bernoulli’s principle also lowers pressure at the stern. Bernoulli’s principle—where the flow is fastest, pressure is lowest—holds airplanes in the sky. Air flows faster over the top of a wing than under the bottom, because of the wing’s shape. Water flows faster between a stern and a bank than on the other side of a ship. It has to, in the restricted space. Reacting to the lowered pressure, the stern is sucked in toward the bank. You try to anticipate suction and start compensating before it comes. In a bend in a narrow channel “suction steers the ship,” according to Hooyer. To fight suction, you may have to go through a left-hand bend in the canal on hard-right rudder, scuttling

suez bernoulli's