The bay plan you see in a liner office or on the bridge is the end product. Behind it sits a planning process: deciding which container goes into which slot under many constraints at once. This guide looks at bay planning from the planner's side. If bay-row-tier coordinates are still new to you, start with how to read a bay plan.
Inputs before you start
A good bay plan starts with complete data. Mistakes at this stage carry through to every slot.
| Input | Main content | Usual source |
|---|---|---|
| Vessel profile | Bays, rows and tiers; stack weight and height limits; reefer socket positions; hatch cover layout | Ship's data, Cargo Securing Manual |
| Port rotation | Order of calls and expected loads and discharges at each port | Liner schedule |
| Cargo on board | Containers loaded at previous ports | BAPLIE message |
| Load list | Container number, size, ISO type, VGM, POD, reefer, DG and OOG status | Bookings and terminal |
| Terminal plan | Number of quay cranes, work sequence, yard positions | Terminal |
Weights must be the VGM required by SOLAS VI/2, not the estimate on the booking.
Step 1: pre-stow by discharge port
Pre-stow (also called strategic stowage or slot allocation) splits the ship into blocks per port of discharge before individual container numbers are assigned. Many carriers do this centrally and let the terminal fill in the detailed slots.
The principles are simple:
- Next port on top. Within a stack, boxes for an earlier port must sit above boxes for a later port. If the order is reversed you have an overstow.
- Deck must not block the hold. Deck boxes stand on the hatch cover. If the hold below contains cargo for port B, every deck box on that cover must come off at port B or earlier.
- Few PODs per bay. Clean POD blocks per bay make crane work easier and reduce the risk of restows when late bookings arrive.
- Spread the crane work. If three cranes will work port B, its cargo should be spread over several bays that are well apart, not piled into one bay.
What happens when these rules are broken is covered in container restows and how to reduce them.
Step 2: hold, deck and stack weights
With POD blocks set, the planner decides what goes below and what goes on deck.
Stack weight. Every stack has a maximum total weight, different for 20ft and 40ft and for hold and deck. In the hold the limit comes from tank top and cell guide strength. On deck it comes from the hatch cover, the foundations and the lashing system. The binding figures are in the ship's own documents; never borrow numbers from another vessel.
Heavy boxes low. Heavy containers in the lower tiers lower the ship's centre of gravity (KG) and reduce lashing forces on deck. Light and empty boxes suit the upper deck tiers. Some lashing systems allow exceptions, but only when the lashing calculation shows the stack is within limits.
Mixing 20ft and 40ft. A 20ft box generally may not sit on a 40ft box. A 40ft box on two 20ft boxes is only allowed where the vessel permits it.
Stack height. High cubes add height. In the hold the limit is the clearance under the hatch cover. On deck it is set by the lashing bridges and by bridge visibility under SOLAS V/22.
Step 3: special cargo
| Cargo | Common placement rule | Planner's note |
|---|---|---|
| Reefers | Powered slots only; reachable for monitoring | Sockets are limited; check set points with the reefer tool |
| Dangerous goods | Per IMDG Code stowage category and segregation | Away from accommodation and heat sources where required |
| OOG (flat rack, open top) | Usually the top tier; adjacent slots may be lost | Over-height and over-width count as lost slots |
| 45ft boxes | Only bays and tiers designed for 45ft, often on deck | Check the overhang into the next bay |
| Empties | Upper deck tiers or filling leftover slots | Light, helps keep KG down |
For dangerous goods, use the licensed current edition of the IMDG Code; the concepts are summarised in IMDG Code basics.
Hatch covers and crane sequence
Lift-away hatch covers come as one or more pontoons per bay. To work the hold, every deck box on that pontoon has to come off and the crane then lifts the pontoon. Each opening adds crane moves that move no cargo, so planners try to:
- open each hold as few times as possible per port;
- use the pontoon split (for example port, centre and starboard pontoons) so only part of the deck is cleared;
- build the discharge and load sequence so cranes never wait.
Worked example: planning bay 14 of a feeder
Illustrative example, not a real ship. A feeder's bay 14 (40ft) has 4 rows, 3 hold tiers, 2 deck tiers and a single hatch cover. Rotation: Tanjung Priok (load) → Surabaya → Makassar → Bitung. Weights in tonnes (VGM).
| Tier | Row 04 | Row 02 | Row 01 | Row 03 |
|---|---|---|---|---|
| 84 (deck) | Surabaya 8 t | Surabaya 10 t | Surabaya 9 t | Surabaya 7 t |
| 82 (deck) | Makassar 18 t | Makassar 22 t | Makassar 21 t | Makassar 16 t |
| Hatch cover | — | — | — | — |
| 06 (hold) | Makassar 14 t | Makassar 15 t | Makassar 16 t | Makassar 12 t |
| 04 (hold) | Bitung 24 t | Bitung 26 t | Bitung 25 t | Bitung 22 t |
| 02 (hold) | Bitung 28 t | Bitung 30 t | Bitung 29 t | Bitung 27 t |
The planner's checks:
- Overstow: in every stack the earlier port is on top. No overstows.
- Hatch cover: the hold is first opened at Makassar, by which time the Surabaya boxes are gone and the Makassar deck boxes come off anyway. No hatch-cover restows.
- Stack weight: the heaviest hold stack, row 02, is 30 + 26 + 15 = 71 t; the deck stack in row 02 is 22 + 10 = 32 t. Both must be below the vessel's 40ft stack limits (see the ship's documents).
- Weight grading: heavy boxes are low in the hold. On deck the heavier Makassar boxes sit in tier 82 and the light Surabaya boxes in tier 84, so POD order and weight grading agree.
- Late cargo: if Surabaya adds boxes for Bitung, free deck slots only work if those boxes do not block the hatch opening at Makassar. This is why multi-port planning matters.
You can try slot and TEU counts per bay in the container stowage calculator and check the resulting BAPLIE with the BAPLIE viewer.
Stability and strength: the final check
A tidy bay plan is not automatically a safe one. Once every bay is filled, the planner checks GM, trim, drafts, shear forces and bending moments, then adjusts ballast or swaps container blocks between bays. The basics are in ship stability basics for planners.
STOWAGE.ID Vessel Stowage helps build the pre-stow, check stack limits and run stability from shore for container ships. It is planning and decision support; the vessel's class-approved loading computer and stability booklet remain the official reference, and the final plan is accepted by the chief officer and master.