cant

A cant is a wooden or steel brace fitted between the deck and the underside of a bulkhead to carry vertical load and prevent flexing or buckling of the bulkhead under pressure or the weight of cargo stacked above. In traditional wooden vessels, cants were hewn from compass timber or straight stock, fitted vertically or at a slight angle, and secured at both deck and bulkhead with bolts or heavy fastenings. Modern steel ships use rolled steel sections or built-up plate girders for the same purpose, though the term persists in shipyard practice.

Cants serve two distinct functions. Under static conditions, they prevent bulkheads from bowing outward when cargo holds are loaded unevenly or when a tank adjacent to the bulkhead is filled with heavy liquid. During rough seas, they resist the dynamic forces that cause bulkhead vibration and the cracking of welds or rivets. A bulkhead without adequate cants can experience permanent set or structural failure, which is why their placement and sizing are governed by classification society rules.

Cants are not installed continuously along a bulkhead. They are spaced at intervals (typically 6 to 10 feet in cargo vessels) to distribute load while leaving enough open area for access and to avoid obstructing the movement of cargo handling equipment. The number and positioning depend on the bulkhead height, the nature and weight of cargo expected, and the vessel's service (deep-sea, coastal, or inland). Tank-top cants, which rest on the tank top itself rather than on deck beams, are used to support lower portions of bulkheads in double-bottom spaces.

The term 'cant' is thought to derive from the Old Norse and Old English word for an angle or slope, reflecting the original practice of fitting them at an angle rather than purely vertical; later rigid vertical cants became standard. In shipyard speech, workers distinguish between deck cants, tank-top cants, and strut cants, which brace machinery foundations rather than bulkheads.

Corrosion and fatigue are the principal failure modes. Cants in holds where bulk grain or ore is loaded experience higher wear and abrasion, and their connection points are prone to crevice corrosion if not properly sealed. Regular inspection for cracking at the weld toe and measurable loss of cross-section is essential to avoid catastrophic bulkhead failure during heavy weather or shifting cargo.