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The two ships seen here seem almost to be touching the walls of the Miraflores Locks.

"Panamax ships" are the largest ships that can pass through Panama Canal. The size is limited by the dimensions of the lock chambers and the depth of the water in the canal. An increasing number of ships are built to the Panamax limit to carry the maximum amount of cargo through the canal.

The increasing prevalence of vessels of the maximum size is a problem for the canal as a Panamax ship is a tight fit that requires precise control of the vessel in the locks, possibly resulting in longer lock time, and requiring that these ships transit in daylight. Because the largest ships travelling in opposite directions cannot pass safely within the Gaillard Cut, the canal effectively operates an alternating one-way system for these ships.



An officer monitors the clearance of the cruise ship Ryndam as she traverses the lock.

Panamax is determined principally by the dimensions of the canal's lock chambers, each of which is 110 ft (33.53 m) wide by 1,050 ft (320.04 m) long, and 85 ft (25.91 m) deep. The usable length of each lock chamber is 1,000 ft (304.8 m). The available water depth in the lock chambers varies, but the shallowest depth is at the south sill of the Pedro Miguel Locks and is 41.2 ft (12.56 m) at a Miraflores Lake level of 54 ft 6 in (16.61 m). The height of the Bridge of the Americas at Balboa is the limiting factor on a vessel's overall height.

The maximum dimensions allowed for a ship transiting the canal are:[1]

  • Length: 965 ft (294.13 m)
  • Beam (width): 106 ft (32.31 m)
  • Draft: 39.5 ft (12.04 m) in tropical fresh water (the salinity and temperature of water affect its density, and hence how deep a ship will float in the water)
  • Air draft: 190 ft (57.91 m) measured from the waterline to the vessel's highest point

A Panamax cargo ship would typically have a DWT of 65,000-80,000 tonnes and a maximum cargo intake of 52,500 tonnes.[2]



Panamax container ship transiting the Panama Canal. Some containers have been offloaded and are transported by the Panama Railway over the isthmus to allow acceptable draft.

Vessels up to 205 ft (62.48 m) in height may pass by prior approval, co-ordinated with low tide at the Bridge of the Americas.

From time to time, vessels up to 107 ft (32.61 m) in beam may be permitted to transit, subject to additional draft constraints.

Vessels with structures extending beyond the maximum length and/or beam above the level of the lock walls may be permitted transit subject to inspection and approval.

When the water level in Lake Gatún is low during an exceptionally dry season the maximum permitted draft may be reduced.

The longest ship ever to transit was the San Juan Prospector, now Marcona Prospector, an ore-bulk-oil carrier that is 973 ft (296.57 m) long, with a beam of 106 ft (32.31 m).[3] The widest ships to transit are the two North Carolina class battleships, USS North Carolina (BB-55) and USS Washington (BB-56), which have beams of 108 ft (32.92 m).[4]

Post-Panamax ships

Post-Panamax or over-Panamax denote ships larger than Panamax that do not fit in the canal, such as supertankers and the largest modern container ships. The 'largest oil tanker in the world' - whichever ship held the title at the time - has not been able to transit the Panama Canal at least since the 'Idemitsu Maru' was launched in the 1960s; she was about 150,000 deadweight tons. U.S. Navy supercarriers are also in the post-Panamax class; the Nimitz class aircraft carriers are 1,092 ft (332.84 m) long overall with a beam of 134 ft (40.84 m), while the flight deck is 252 ft (76.81 m) wide.


USS Missouri, one of the Iowa-class battleships, makes a very tight fit as she passes through the Miraflores Locks of the Panama Canal in October 1945.
Panamax car-carrier ship transiting the Panama canal. The hull construction, meant to maximize cargo capacity, also allows the ship to narrowly pass through the canal.

As early as the 1930s, new locks were proposed for the Panama Canal to ease congestion and to allow larger ships to pass.

On October 22, 2006, the Panama Canal Authority (with the support of the Electoral Tribunal) held a referendum for Panamanian citizens to vote on the Panama Canal expansion project. The expansion was approved by a wide margin, with support from about 78% of the electorate. It is estimated that the project will be completed by 2014 and will cost $5.3 billion; this sum is expected to be recovered within 11 years.

After this expansion, the Panama Canal will be able to handle vessels of cargo capacity up to 13,000 twenty-foot equivalent units (TEU)[5]; currently, it can only handle vessels up to about 5,000 TEU.[6] A third set of locks – 1,400 ft (426.72 m) long, 180 ft (54.86 m) wide, with a draft of 60 ft (18.29 m) – will supplement the two existing sets.

Comparison of sizes

Class Panamax Panamax II
Length 1,050 ft (320.04 m) 1,400 ft (426.72 m)
Width 110 ft (33.53 m) 180 ft (54.86 m)
Draft 41 ft (12.50 m) 60 ft (18.29 m)
TEU 5000 12000

New Panamax

Plans to build bigger locks have led to the creation of "New Panamax", with maximum length overall of 1,200 ft (365.76 m), beam 160 ft (48.77 m) and draft in tropical freshwater 50 ft (15.24 m).[7] Naval architects and civil engineers are already taking into account these dimensions for container ships.[8] The world's largest cruise ship Oasis of the Seas has almost New Panamax dimensions with height difficult to pass under the Bridge of the Americas even at low tide.

However, even before the revised dimensions were announced, the Maersk E-class - like the Emma Maersk; as well as many large tankers - ULCCs; and some bulk carriers, VLOCs - will not be able to pass through even the new, much larger locks.

See also


  1. ^ Vessel Requirements, from the Panama Canal Authority
  2. ^ Modern ship size definitions, from Lloyd's register
  3. ^ Background of the Panama Canal, Montclair State University
  4. ^ Battleships, United States Battleships in World War II, by Robert O. Dulin, Jr. and William H. Garzke, Jr.; pages 62 and 145. Naval Institute Press, 1976. ISBN 0-87021-099-8
  5. ^ "Maersk Edinburgh" 13,000 TEU container ship (Rickmers Maritime)
  6. ^ "Maersk Djibouti" 5,000 TEU container ship (Rickmers Maritime)
  7. ^ ACP: Dimensions for Future Lock Chambers and “New Panamax” Vessels
  8. ^ Propulsion Trends in Container Vessels MAN B&W Two-stroke Engines

External links


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

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Panamax (not comparable)


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  1. The maximum width, length, and draft of a ship that can transit the locks on the Panama Canal.


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