When I train junior planners, I always ask the same question:
“If you load a vessel to maximum capacity and the stability software shows all green, is that an optimized plan?”
90% say yes.
They’re wrong.
The Southampton Disaster
A few years ago, a junior planner loaded an Asia-North Europe mainliner. The vessel departed China with 8 tiers on deck. Stability: green. Stress limits: green. Lashing: green. Everything perfect.
The vessel was scheduled for Southampton.
One problem: Southampton’s terminal cranes could only reach 6 tiers.
Nobody checked.
The vessel arrived in the English Channel and couldn’t discharge. Containers on tiers 7 and 8 were inaccessible. The terminal physically couldn’t reach them.
The solution:
Change of Rotation. The vessel diverted to Rotterdam first. In Rotterdam, they discharged cargo from the top tiers to make the Southampton cargo accessible. Then sailed to Southampton. Then back to continue the rotation.
The cost:
Approximately 100 restows in European terminals. At €250-350 per move: €25,000-35,000.
Plus fuel for the detour. Plus schedule delays. Plus knock-on effects across the entire rotation. Plus angry customers waiting for cargo.
Total damage: approximately €50,000-70,000.
Because someone loaded 8 tiers without checking that Southampton could only handle 6.
The Paradox Nobody Teaches
Here’s what the stability software shows you:
- GM: ✓ Green
- Shear Force: ✓ Green
- Bending Moment: ✓ Green
- Lashing: ✓ Green
- Draft: ✓ Green
Here’s what the stability software doesn’t show you:
- Can the destination terminal reach your top tier?
- Can you enter the port with this draft at low tide?
- Does the berth have air draft restrictions?
- Can the port handle your crane split efficiently?
- Is there a tidal window you’ll miss if you load too deep?
“All green” means the vessel is safe to sail.
It doesn’t mean you can actually discharge at your destination.
Port Constraints That Kill Plans
Every port has limitations. A planner who doesn’t know them creates disasters.
Tier Reach Limits
| Port type | Typical max tier | What happens if exceeded |
|---|---|---|
| Modern mega-terminal | 9-10 tiers | Usually fine |
| Regional terminal | 6-7 tiers | COR or restow at previous port |
| Small feeder port | 5-6 tiers | Cargo stays on board |
Southampton, Felixstowe, and other established ports often have older cranes. They weren’t built for 10-tier vessels. Load 8 tiers for these ports, and you have a problem.
Draft Restrictions
| Constraint | Impact |
|---|---|
| Channel depth | Maximum arrival draft |
| Berth depth | Maximum alongside draft |
| Tidal window | When you can enter/exit |
| Under-keel clearance | Safety margin required |
Many ports have draft limits that change with tide. You can enter at high tide with 14m draft. At low tide, maximum is 12m.
Load to 14m draft without checking tidal windows? You wait 6-12 hours for the tide. Or you anchor and lighter cargo onto barges. Both cost money.
Air Draft Restrictions
Bridges, power lines, and port infrastructure limit how high your deck cargo can be.
| Example | Air draft limit | Impact |
|---|---|---|
| Under a bridge | 45-55m from waterline | Limits deck tiers |
| Near airport | Varies | Height restrictions |
| Old port infrastructure | 40-50m | Can’t stack high |
Air draft = height from waterline to top of highest container. Load too high, and you can’t pass under the bridge to reach the berth.
Crane Configuration
| Port | Cranes | Impact on planning |
|---|---|---|
| Major hub | 4-6 STS cranes | Plan for even split |
| Regional port | 2-3 cranes | Longer port stay |
| Small port | 1-2 mobile cranes | Very limited capacity |
A plan optimized for a 4-crane terminal fails at a 2-crane port. The crane split becomes unbalanced. Port time doubles.
What “Optimized” Actually Means
An optimized plan isn’t the plan that loads the most cargo.
An optimized plan is the plan that loads the most cargo THAT CAN ACTUALLY BE DISCHARGED at every port in the rotation.
This requires studying constraints before loading:
Before accepting cargo:
- What’s the tier limit at each port?
- What’s the draft limit at each port?
- What tidal windows exist?
- What crane configuration does each terminal have?
Before building the plan:
- What’s the maximum draft we can have for Port 3 given its tidal window?
- How many tiers can we stack for Port 5 given its crane reach?
- What’s the air draft limit for Port 7?
Before departing:
- Does this plan work for EVERY port, not just the first one?
- If we load this extra cargo, can we still make the tidal window in Port 4?
- Are we creating problems downstream to solve problems today?
The Waiting Game
Let me quantify what ignoring constraints costs:
Scenario: Draft too deep, must wait for tide
| Factor | Cost |
|---|---|
| 6 hours waiting at anchor | Fuel: $1,500-2,500 |
| Missed berth window | Delay: 12-24 hours |
| Crew overtime | $500-1,000 |
| Schedule disruption | Knock-on delays |
| Customer impact | Late deliveries |
Conservative total per incident: $5,000-15,000
Scenario: Tier limit exceeded, COR required
| Factor | Cost |
|---|---|
| Detour to intermediate port | Fuel: $10,000-20,000 |
| Restows (50-100 moves) | $15,000-35,000 |
| Schedule delay | 24-48 hours |
| Customer claims | Variable |
| Reputation damage | Long-term |
Conservative total per incident: $30,000-70,000
This happens on feeders more than you’d think. Not because the planners are incompetent, but because nobody has time to check every constraint at every port.
Why This Happens on Feeders
On mainliners, we study port constraints obsessively.
Before every rotation, the shore planning team reviews:
- Draft limits at every port
- Tidal windows and schedules
- Terminal crane specifications
- Air draft restrictions
- Berth limitations
This information is built into the planning process. You can’t load 8 tiers for a 6-tier terminal because the system blocks it.
On feeders, this infrastructure doesn’t exist.
The Chief Officer receives a load list. They have 3-4 hours. They check stability. They verify lashing. They confirm the plan is legal.
Nobody asks: “Can Rotterdam’s terminal actually reach tier 8?”
Nobody checks: “What’s the tidal window in Bilbao?”
Nobody verifies: “Does this draft work for every port?”
The plan is legal. It might not be executable.
The Real Definition of Planning
Planning isn’t putting containers in slots until the software shows green.
Planning is defining the optimal rotation given all constraints.
This means:
- Maximum cargo capacity that every port can handle
- Draft profile that works with every tidal window
- Tier heights that every terminal can reach
- Crane splits that every port can execute efficiently
The best plan isn’t the fullest plan. It’s the plan with the winning strategy.
A plan that loads 95% capacity and executes perfectly beats a plan that loads 100% capacity and causes a €50,000 COR.
The Constraint Checklist
Before finalizing any plan, these questions need answers:
| Constraint | Question | Who checks? |
|---|---|---|
| Tier reach | Can every discharge port reach our max tier? | Planner |
| Draft | Do we fit every port at expected tide? | Planner |
| Air draft | Any bridges or height restrictions? | Planner |
| Tidal window | Will we make the window or wait? | Planner |
| Crane config | Is our split balanced for 2/3/4 cranes? | Planner |
| Berth length | Does vessel fit the assigned berth? | Operations |
On feeders, who’s checking these? Usually nobody.
What Changes With Proper Planning
Before (load to max, hope it works):
- Load maximum cargo
- Stability shows green
- Depart
- Discover problems at destination
- Emergency solutions (COR, waiting, restows)
- Costs: $10,000-70,000 per incident
After (plan to constraints):
- Study all port constraints
- Define maximum feasible cargo per port
- Load within those limits
- Execute smoothly
- Costs: Zero emergency costs
The second approach might load 3-5% less cargo occasionally. But it never causes a €50,000 COR.
Reliability beats maximum capacity every time.
The Question for Operators
When your Chief Officer builds a stowage plan, do they have:
- Tier reach limits for every port?
- Draft restrictions and tidal schedules?
- Air draft limitations?
- Terminal crane specifications?
Or do they have:
- A load list
- 3 hours
- A stability calculator
The first creates executable plans. The second creates legal plans that might fail downstream.
Southampton taught us: “all green” isn’t enough.
You need someone who knows every port’s constraints before the first container is loaded.
“All green” keeps you safe. Knowing your constraints keeps you profitable.