How Are Containers "Berthed" on a Ship? The High-Stakes Game of Tetris

Imagine you have to pack a suitcase. You put the heavy shoes at the bottom and the fragile shirts on top. Easy, right?

Now imagine packing a suitcase with 24,000 metal boxes, each weighing up to 30 tons. Some are explosive, some need electricity, and they have to be unloaded at five different countries in a specific order. Oh, and if you mess up, the ship might snap in half or capsize in a storm.

This is the job of a Stowage Planner.

When a container is "birthed" (or technically, stowed) on a vessel, it isn't placed randomly. It is assigned a specific 3D coordinate that dictates exactly where it lives for the voyage. Here is how the logic works.

How Are Containers Arranged on a Ship? (The Art of Stowage) 

1. The Golden Rule: Heavy Goes Low

The most critical rule of ship stability is keeping the Center of Gravity low.

• Below Deck: The heaviest containers (carrying metals, liquids, machinery) are stowed deep inside the ship's hold, below the waterline. This acts like ballast, keeping the ship stable in rough waves.

• Above Deck: Lighter containers (carrying clothes, electronics, empty boxes) are stacked high on top of the hatch covers.

If you put heavy boxes on top, the ship becomes "top-heavy" and could roll over.

2. The "First Out" Rule (Port Rotation)

Ships stop at multiple ports (e.g., Shanghai -> Singapore -> Rotterdam -> Hamburg).

• The Logic: You cannot bury a container meant for Singapore underneath a stack of containers meant for Hamburg.

• The Reverse: Containers for the last port are loaded first (at the bottom). Containers for the next port are loaded on top.

• Restows: If a planner makes a mistake, the crane has to dig out the buried container, move the top ones onto the dock, and then put them back. This is called a "Restow," and it costs the shipping line thousands of dollars in wasted time.

3. The "Address" of a Container (Bay-Row-Tier)

Every slot on a ship has a unique 6-digit ID number, known as the Bay-Row-Tier system. It works just like a cinema seat number.

• Bay (Where along the length?): Numbered from Bow (front) to Stern (back). Odd numbers (01, 03, 05) are for 20ft containers. Even numbers (02, 04, 06) are for 40ft containers.

• Row (Where across the width?): Numbered from the center out. Center is 00. Port side (left) is even (02, 04). Starboard side (right) is odd (01, 03).

• Tier (How high up?): Numbered from the bottom up. 02 is the floor of the hold. 82 is high up on deck.

So, if your container is at Bay 19, Row 02, Tier 84, the crane operator knows exactly where to find it.

4. Special VIP Handling

Some containers are high-maintenance:

• Reefers: Must be placed near "Reefer Plugs" (electrical sockets) to keep the motor running.

• Dangerous Goods (DG): Explosives or flammables are kept away from the crew quarters and away from the engine room (heat source). They are also usually stowed on deck so that, in a worst-case fire scenario, they are accessible to fire hoses.

• OOG (Out of Gauge): Oversized flat racks are usually placed on the very top of a stack or in "open" rows because they don't fit in standard slots.

5. Who Does the Math?

In the old days, the ship's Chief Officer did this with paper and pencil. Today, it is done by specialized Stowage Coordinators working in offices in Hamburg or Singapore, using powerful software like MACS3 or Capstan.

These programs calculate the ship's stability, shear forces, and wind resistance in real-time. The plan is then emailed to the ship's captain and the terminal stevedores before the ship even arrives.

Summary

A container ship looks like a chaotic wall of colorful bricks, but it is actually a masterpiece of mathematics. Every single box is sitting in the only spot it could possibly be.

At TraceContainer.com, when you track your shipment, you are seeing the result of this precise planning in action.