When you see a container vessel listed in PortWatch as “Container Ship” or “Fully Cellular Container”, the AIS type code does not tell you anything about her size class. Container ships are categorised informally by capacity (in TEU, twenty-foot equivalent units) and by the dimensional limits of the major canals and ports they can transit. This guide walks through the standard categories and what they mean operationally.
Feeder and Feedermax
Feeder vessels carry up to about 1,000 TEU and serve as the short-haul connectors between regional hub ports and smaller secondary ports that mainline services do not call at directly. Feedermax vessels carry up to about 3,000 TEU and operate on slightly longer regional trades. Both classes typically have on-board cranes (geared) so they can call at ports without ship-to-shore gantry cranes.
Panamax
The original Panamax class, set by the dimensional limits of the historical Panama Canal locks (32.31 m beam, 294.13 m length overall, 12.04 m draft), corresponds to about 5,000 TEU capacity. Vessels designed exactly to these limits are now considered medium-sized. The category is named for what the vessel could transit, not for any feature of the vessel itself.
Post-Panamax
Post-Panamax vessels exceed the dimensions of the original Panama Canal locks but predate the new (expanded) locks. They carry roughly 5,000–10,000 TEU and historically routed Asia-to-US-East-Coast trade via Suez or via the US West Coast and intermodal rail rather than via Panama. With the 2016 opening of the new Panama locks, much of this traffic shifted back to the all-water Panama route.
New Panamax / Neo-Panamax
New Panamax (also Neo-Panamax) vessels are built to the dimensional limits of the new Panama Canal locks (49 m beam, 366 m length overall, 15.2 m draft), which corresponds to roughly 14,000 TEU. The label is a planning category as much as a vessel size — operators use it to mean “the largest vessel we will route through Panama”.
Ultra Large Container Vessel (ULCV)
ULCVs carry over 14,500 TEU and today reach 24,000+ TEU on the largest classes (HMM Algeciras, Ever Ace, MSC Irina). At these sizes the vessels are too large for the Panama Canal and require dedicated deep-water berths with very tall ship-to-shore cranes. ULCVs are typically restricted to the Asia–Europe trade via Suez and to a small number of mega-hub ports — Rotterdam, Antwerp, Hamburg, Singapore, Shanghai, Ningbo, Shenzhen — that have been physically rebuilt to handle them.
Why size classes matter to a port
A port’s ability to handle a given size class is set by berth depth, crane outreach, and yard capacity. A port that lists Feeder and Panamax vessels in its calls but no Neo-Panamax or ULCV calls is almost certainly bound by one of those three constraints. In practice the binding constraint is most often crane outreach: many ports have adequate depth but lack the very tall STS cranes needed to reach across a 22-row-wide ULCV.