Which type of vessel is too large to fit through the Panama Canal?

The term "Post Panamax" refers to vessels that are larger than the dimensions of the original locks of the Panama Canal, which were designed to accommodate Panamax ships. The original locks can handle vessels up to 965 feet in length and 106 feet in beam, hence vessels exceeding these dimensions are classified as Post Panamax.

The expansion of the Panama Canal, completed in 2016, introduced larger locks to accommodate Neopanamax vessels, which can measure up to 1,200 feet in length and 160 feet in beam. However, ships classified as Post Panamax still remain too large to traverse the older locks.

Panamax vessels are specifically designed to be just within the size limits of the original canal, while Coastwise vessels generally operate in domestic waters along the coasts and are not categorized based on canal dimensions. Thus, the Post Panamax classification signifies that these vessels cannot fit through the original locks of the canal, making it the correct answer.