Bay is one of three coordinates in the Bay-Row-Tier (BRT) system used to identify the exact stowage position of every container aboard a ship.
The Bay-Row-Tier System
A container’s stowage address combines bay (fore-to-aft position), row (port-to-starboard position), and tier (vertical level). Bay is the lengthwise piece: picture the ship sliced into transverse sections from bow to stern, like ribs — each slice is one bay, and every container within that slice, at any row or tier, belongs to that bay number.
How Bays Are Numbered
Bays are numbered sequentially along the ship’s length, conventionally in odd numbers for standard 40-foot-equivalent bay positions with even numbers sometimes used for 20-foot subdivisions within a 40-foot bay — the exact convention is fixed per vessel and documented in that ship’s container stowage plan, so numbering is always consistent for a given ship even though it can differ slightly between vessels.
Why Bay Position Matters
Bay position feeds directly into the ship’s longitudinal stress and trim calculations — cargo weight distributed unevenly along the vessel’s length (heavier at certain bays than others) creates bending moments and shear forces the hull must safely withstand, and affects trim (the ship’s fore-and-aft balance). The loading computer checks bay-by-bay weight distribution against the vessel’s approved stress limits before any load plan is finalized.
Bay in Practice
Terminal operators plan crane sequencing bay by bay during loading and discharge, since a crane services one bay at a time, and the ship’s own cargo plan documentation is organized around bay numbers to keep stowage, stability, and stress calculations all referencing the same coordinate system.
Exam Relevance
The Bay-Row-Tier stowage system, including bay numbering and its link to longitudinal stress and trim, is covered under container ship cargo operations and stability topics in deck officer competency exams.