Tier 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 full stowage address combines bay (fore-to-aft position), row (port-to-starboard position), and tier (vertical level) — for example, “06-08-82” identifies one specific container slot. Tier is the vertical piece of that address, telling planners and crew exactly which level a container sits at, whether stacked below deck in a hold or above deck on deck.
How Tiers Are Numbered
Tiers are conventionally numbered in even numbers counting upward — starting from the bottom of the hold (below deck) and, following common industry practice, restarting from a different even number (often 82) for the first tier above deck, so that below-deck and above-deck positions are never confused even though both count upward from their own base.
Why Tier Position Matters
Tier position is directly tied to some of the most safety-critical calculations in container operations: stack weight limits (how much weight the bottom container in a stack can safely bear from everything above it), stability (higher tiers raise the ship’s center of gravity, reducing GM), and lashing requirements (upper tiers typically need different securing arrangements than lower ones due to greater leverage from ship motion). Getting tier assignment wrong in the stowage plan has real consequences for all three.
Tier in Practice
The ship’s loading computer checks proposed stowage against tier-specific stack-weight and stability limits before a load plan is finalized, and stevedores follow bay-row-tier instructions precisely during loading and discharge to ensure containers end up exactly where the approved plan places them.
Exam Relevance
The Bay-Row-Tier stowage system, including tier numbering and its link to stack-weight and stability limits, is covered under container ship cargo operations and stability topics in deck officer competency exams.