A stowage plan decides where each container goes on a ship: its bay, row and tier, together with its weight, port of discharge and special status such as reefer or dangerous goods. It has three jobs at once: keep the ship stable and within its structural limits, keep the cargo safe at sea, and let every port work the ship without unnecessary moves. This guide covers who makes the plan, what data it needs, the constraints it must satisfy, and how it differs from a container load plan.

Two levels of load planning

The word "plan" is used at two quite different levels:

Level Question answered Typical document Prepared by
Ship Which container in which slot? Stowage plan, bay plan, BAPLIE Line planner, terminal planner, chief officer
Container/truck Which goods where inside the unit? Container load plan, packing list Shipper, forwarder, warehouse

The two levels depend on each other. The container weights a ship planner uses come from the VGM, and an accurate VGM starts with a correct load plan in the warehouse.

Who makes the stowage plan

On container services, the work usually flows like this:

  • The line's central planner prepares a pre-plan for the whole rotation: space allocations per port of loading and discharge, reefer slots and areas for dangerous goods.
  • The terminal's ship planner builds the detailed loading plan from the containers that have actually arrived in the yard, the crane work sequence and yard stack positions.
  • The chief officer checks the plan on the ship's loading computer and has the authority to reject it or demand changes if stability, strength or safety are not met.

When loading is complete, the final plan is sent to the next port, usually as a BAPLIE message standardised by SMDG.

Input data

A planner cannot work without complete and timely data:

  • Booking and loading lists: number, size and type of containers per destination, including ISO type codes such as 22G1 or 45G1.
  • VGM: the verified gross mass of each container, mandatory before loading.
  • Dangerous goods (DG): IMDG class, UN number and segregation requirements. See IMDG Code basics.
  • Reefers: set temperature and power requirements; reefer plugs on board are limited.
  • Out of gauge: cargo that exceeds container dimensions, for example on flat racks, needs extra space.
  • Port rotation (POD): the order of discharge ports decides which containers must sit on top.

Constraints the plan must satisfy

At a high level, a stowage plan has to respect the following. The actual numbers always come from the individual ship's manuals and loading computer.

  • Stability: sufficient metacentric height (GM), acceptable trim and draft, and heel that can be controlled with ballast.
  • Longitudinal strength: shear forces and bending moments in the hull must stay within limits.
  • Stack weights: every 20' and 40' stack has a maximum weight set by the shipbuilder.
  • Lashing: forces on lashings and twistlocks must stay within the ship's securing system limits; tall stacks with heavy boxes on top exceed these quickly.
  • Bridge visibility: deck stacks must not block the view from the bridge beyond what SOLAS allows.
  • DG segregation and reefer slots: dangerous goods are separated per the IMDG Code; reefers go only where there are plugs.
  • Overstowage: containers for the next port must not be buried under containers for later ports, or the terminal will have to restow.

The loading computer and final approval

The loading computer is software on board that holds an approved model of the ship: tanks, cargo spaces, strength limits and stability curves. Terminal planners usually work in their own planning software too, but the figures that count are those from the ship's loading computer. A typical sequence:

  1. The terminal or line sends the loading plan to the ship before operations start.
  2. The chief officer imports it and checks GM, trim, draft, shear forces, bending moments, stack weights and lashing forces.
  3. If anything fails, the chief officer asks for changes: swapping container positions, adjusting ballast or refusing particular containers.
  4. During loading, changes on the quay (cancelled boxes, substitutes, different weights) are logged and recalculated.
  5. Once loading is complete, the departure condition is calculated and the final plan goes to the next port.

Because changes continue to the last minute, accurate weights and container types from shippers reduce the risk of boxes being shut out.

Worked example

Take one 40' deck stack on a feeder vessel rotating Tanjung Priok → Singapore → Port Klang. Assume the ship's manual limits this stack to 90 tonnes (an illustrative figure, not data for any real vessel).

Tier Container POD VGM
88 40' B2 Singapore 10 t
86 40' B1 Singapore 16 t
84 40' C2 Port Klang 24 t
82 40' C1 Port Klang 28 t
  • Stack weight: 28 + 24 + 16 + 10 = 78 t, under the 90 t limit.
  • Discharge order is right: Singapore boxes on top, so no restows.
  • Weight decreases upwards, which helps both stability and lashing forces.

Now suppose B1 was booked at 16 t, but the VGM received shows 30 t. The stack becomes 28 + 24 + 30 + 10 = 92 t, over the limit, with a 30 t box sitting on a 24 t box. The planner has options: move the 30 t box to another stack with spare weight capacity, put it below deck in a bay discharged at Singapore, or change the tier order if the rotation allows. Each option has to be rechecked on the loading computer. This is why accurate weights from the warehouse onwards matter so much.

Common mistakes

  • Assuming booking weights equal real weights. Weight surprises break a plan that was already calculated.
  • Late VGM or DG data. The container can miss the vessel.
  • Ignoring centre of gravity inside the container. A box with its cargo bunched at one end is harder to handle and lash. See centre of gravity and weight distribution.
  • Confusing a load plan with a stowage plan. A shipper's load plan does not replace the ship's plan.

Stowage.id and the container load plan

Stowage.id is a tool for planning cargo inside containers and trucks, not a vessel planning system. The Load Planner helps you build a container load plan: carton and pallet positions, gross weight and the centre of gravity inside the box. You can use that data to prepare a VGM form and check container payload. To understand container positions on the ship, continue with how to read a bay plan and the VGM SOLAS guide. Every Stowage.id result is a simulation and does not replace official weighing, the ship's loading computer or the approval of the chief officer and terminal operator.