Length Overall

Length overall, abbreviated LOA, is the total extreme length of a ship measured between its two furthest points fore and aft, including any parts of the structure that project beyond the hull proper such as a bulbous bow below water or overhangs at the stern. It is the largest of the several length measurements used for a ship and is the one that governs the physical space the vessel occupies, which is why it is so important for the practical business of fitting a ship into the places it must go.

LOA is the critical dimension whenever a ship's physical envelope must be accommodated. Ports specify the maximum LOA their berths can take; canal and lock authorities, such as those of the Panama and Suez Canals, define maximum lengths for transit; and dry docks and shipyards are limited in the length of vessel they can handle. The famous ship-size categories are defined partly by these constraints — Panamax and Neopanamax vessels, for instance, are sized to the dimensions of the Panama Canal locks, of which length overall is one limiting factor alongside beam and draft. Manoeuvring and berthing calculations, the room needed to turn, and the arrangement of mooring all depend on LOA.

LOA should be distinguished from the other length measurements naval architects use. Length between perpendiculars is measured between defined points at the bow and stern at the waterline and is used in many design and stability calculations, while the length on the waterline is the length actually in contact with the water at a given draft. These are generally shorter than LOA. Because it captures the full extent of the ship, LOA is the figure quoted first when describing how big a vessel is in terms of the space it needs, and it is central to port planning, canal transits, docking and safe ship handling.