Cargo Vessel Size Classifications

Find out which factors determine the size a shipping classification

Container Ship Bow

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Cargo shipping is a low-margin business model that requires vessels to be fully loaded in order to sustain profitable operations. When a ship is in the design phase it's almost always structured in a specific classification of naval architecture and built to serve a specific route or purpose.

Measuring Terminology

Vessels built to pass through specific bottlenecks while carrying the maximum amount of cargo are termed “max.” (For example, freighters designed to pass through the Panama Canal are called Panamax.) This means the ship will fit into a minimum bounding box that matches the dimensions of the smallest locks in the canal. Bounding boxes are measured three-dimensionally. In addition to maximum length and width, the measurements include areas underwater and above the deck.

In maritime-specific cases, the dimensions of a bounding box have some different but still familiar names:

  • Draft is the measurement from the surface of the water to the bottom.
  • The beam is the width of a vessel at its widest point.
  • Length is measured as the overall length of a ship, however, in some cases, maximum dimensions might take into consideration the length at the waterline which can differ significantly from length overall (LOA) due to the deadrise of the hull.
  • Air Draft is the measure of the maximum height above the waterline of any structure on the ship.
  • Gross Tonnage (GT) and Dead Weight Tonnage (DWT), while thought by many to be measures of weight, are more accurately described as measures of the volume of a vessel’s hull. Weight only factors in when an equivalent weight of water displaced by the hull must also be expressed.

Ship Size Classification Definitions

Most of these definitions pertain to cargo vessels but they can be applied to any kind of ship, including military and cruise ships.

Aframax—This classification almost always refers to oil tankers, although it's occasionally applied to other bulk commodities. These vessels serve oil-producing areas with limited port resources or where man-made canals lead to terminals that load raw petroleum products.

The size limitations in this class are few. The main restriction is the beam of the vessel, which in this case cannot exceed 32.3 Meters or 106 feet. The tonnage of an Aframax is approximately 120,000 DWT.

Capesize—This is an example in which the naming scheme varies but the sizing concept is the same. Capesize vessels are large bulk carriers and tankers that get their name from the route they must take to bypass the Suez Canal. Depending on the ship's final destination, this route takes them past the Cape of Good Hope in Africa or Cape Horn of South America.

A Capesize ship is limited by the depth of the Suez Canal which is currently 62 feet or about 19 meters. The displacement of these vessels can range from 150,000 to as much as 400,000 DWT. The soft geology of the region has allowed the canal to be dredged to a greater depth since it was first built, and it's possible the canal will be dredged again in the future. As a result, the maximum draft limit of classification may change as well.

Chinamax—The Chinamax classification is determined by the size of port facilities rather than by physical obstructions or limitations associated with a specific waterway. As a result, the term is not only applied to ships, but also to port facilities themselves. Ports that can accommodate these very large vessels are referred to as Chinamax compatible, whether or not they're anywhere near China. They must meet the draft requirements of dry bulk carriers in the 350,000 to 400,000 DWT range while not exceeding 24 meters or 79 feet of draft, 65 meters or 213 feet of beam, and 360 meters or 1,180 feet of overall length.

Malaccamax—For naval architects designing this class of ship, the main restriction is the draft of the vessel. The Strait of Malacca has a depth of 25 meters or 82 feet so ships of this class must not exceed that depth at the lowest point of the tidal cycle. Vessels serving this route can gain capacity in the design phase by increasing beam and length at the waterline in order to carry a greater capacity in a limited draft situation.

Panamax—Panamax was once the most commonly recognized ship classification due to its derivation from the world-famous Panama Canal. Panamax size limitations are 294 meters or 965 feet in length, 32 meters or 106 feet of beam, 12 meters or 39.5 feet of draft, and 58 meters or 190 feet of air draft so vessels can pass under the Bridge of the Americas.

The Panama Canal opened in 1914. By 1930, there were already plans to enlarge the locks to allow the passage of larger vessels. In 2014, construction for a third larger set of locks that went into operations in 2016, ushered in a new class of vessels called New Panamax.

New (Neo) Panamax—New Panamax has size limitations of 366 meters or 1,200 feet in overall length, 49 meters or about 160 feet of beam, and a draft of 15 meters or 50 feet. The air draft remains the same to accommodate passage under the Bridge of the Americas, which is now the main limiting factor for large vessels passing through the canal.

Seawaymax—This class of vessels is designed to achieve the maximum size for passage through the Saint Lawrence Seaway inbound or outbound from the Great Lakes system. The locks of the Seaway are the limiting factor in this classification. The Saint Lawrence can accommodate ships no larger than 225.5 meters or 740 feet of overall length, about 24 meters or 78 feet of beam, about eight meters or 26 feet of draft, and an air draft of 35.5 meters or 116 feet above the water. Larger vessels that operate on the Great Lakes are unable to reach the sea due to a bottleneck at the locks.

Suezmax—The dimensions of the Suez Canal are the limiting factor for the size of ships in this class. Since there are no locks along the one-hundred-plus miles of the canal, the only limitations are draft and air draft. The canal has a useful draft of 19 meters or 62 feet. Vessels are limited by the height of the Suez Canal Bridge that has a clearance of 68 meters or 223 feet.

Supermax/Handymax—Once again this class of ships is not restricted by a specific set of locks or bridges, but instead, it refers to cargo capacity and the ability to use ports. Ports are often designated to be Supermax or Handymax compatible.

As the name implies, Supermax is the largest of the vessel classifications, with a size of around 50,000 to 60,000 DWT and can be as long as 200 meters or 656 feet. Handymax vessels are slightly smaller and have a displacement of 40,000 to 50,000 DWT. Such ships are usually at least 150 meters or 492 feet.

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