Panamax Explained: Panama Canal Lock Limits, Gatun Lake and Neopanamax

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Panamax is the set of size limits imposed by the Panama Canal's original locks, which opened in 1914 with chambers 1,050 feet long and 110 feet wide. For a century, ships built for global trade were held to about 950 feet in length, with some container and passenger ships allowed to 965 feet, a 106-foot beam and 190 feet of height above the waterline, a ceiling set by the Bridge of the Americas, the Centennial Bridge and the Atlantic Bridge. The draft limit of 39.5 feet is measured in tropical fresh water because ships are lifted 85 feet into Gatun Lake, where warm fresh water near 84 degrees Fahrenheit gives less buoyancy than cold salt water, so hulls ride deeper. An original Panamax ship carries about 52,500 deadweight tons, roughly 5,000 containers. The U.S. Navy designed its Iowa and South Dakota class battleships with a beam of about 108 feet 2 inches to squeeze through the 110-foot locks.

As demand outgrew 5,000-container ships, Panama held a 2006 referendum that passed with about 78 percent approval, and a third set of locks opened in June 2016. The Neopanamax standard allows ships 1,201 feet long, a beam first set at 161 feet and raised to 168.1 feet in 2018, a 50-foot draft, about 14,000 containers and 120,000 deadweight tons. The locks are gravity fed and flush about 50 million gallons of fresh water per ship, so droughts at Gatun Lake have forced the draft limit down to 44 or even 43 feet. Ports raced to keep up: Miami ran its Deep Dredge, Baltimore, Norfolk, New York and New Jersey, Halifax and Liverpool deepened or expanded, and Mexico is building the Interoceanic Corridor of the Isthmus of Tehuantepec as a rail alternative.

• Deadweight tonnage counts cargo, fuel, fresh water, ballast, provisions and crew, not the ship itself.
• The Port Authority spent $1.7 billion to raise the Bayonne Bridge 64 feet by building a new roadway inside the arch above live traffic.
• Mexico's plan unloads ships at Salina Cruz on the Pacific and moves containers by rail to Coatzacoalcos on the Gulf.
• Some Panamax cargo ships only seven years old were sold for scrap once the new locks opened.
• Other owners chose jumboization, cutting hulls in half and welding in a new midsection to widen them.