Saint Lawrence Seaway - Lock and Channel Dimensions

Lock and Channel Dimensions

The size of vessels that can traverse the seaway is limited by the size of locks. Locks on the St. Lawrence and on the Welland Canal are 766 ft (233.5 m) long, 80 ft (24.4 m) wide, and 30 ft (9.14 m) deep. The maximum allowed vessel size is slightly smaller: 740 ft (225.6 m) long, 78 ft (23.8 m) wide, and 26.5 ft (8.1 m) deep; many vessels designed for use on the Great Lakes following the opening of the seaway were built to the maximum size permissible by the locks, known informally as Seawaymax or Seaway-Max. Large vessels of the lake freighter fleet are built on the lakes and cannot travel downstream beyond the Welland Canal. On the remaining Great Lakes, these ships are constrained only by the largest lock on the Great Lakes Waterway, the Poe Lock at the Soo Locks, which is 1,200 ft (365.8 m) long, 110 ft (33.5 m) wide and 32 ft (9.8 m) deep.

A vessel's draft is another obstacle to passage on the seaway, particularly in connecting waterways such as the St. Lawrence River. The depth in the channels of the seaway is 41 ft (12.5 m) (Panamax-depth) downstream of Quebec City, 35 ft (10.7 m) between Quebec City and Deschaillons, 37 ft (11.3 m) to Montreal, and 27 ft (8.2 m) upstream of Montreal. Channel depths and limited lock sizes mean that only 10% of ocean-going ships can traverse the entire seaway. Proposals to expand the seaway, dating from as early as the 1960s, have been rejected as too costly, and environmentally and economically unsound. Lower water levels in the Great Lakes have also posed problems for some vessels in recent years.

While the seaway is currently (2010) mostly used for shipping bulk cargo, the possibility of its use for large-scale container shipping is under consideration as well. If the project goes ahead, feeder ships would take containers from the port of Oswego on Lake Ontario in upstate New York to Melford International Terminal in Nova Scotia for transfer to larger ocean-going ships.