Weather Routing and Voyage Optimisation: Beyond Avoiding Storms

What a routing service actually provides

Weather routing began as a safety service: keep the ship out of the worst weather. It is now three services at once — safety, fuel efficiency, and the evidential basis for defending performance claims — and the third is the one most operators underuse.

That fourth line is the commercially valuable one. When a charterer deducts for underperformance, the argument turns on what the weather actually was, and on the charterparty's definition of good weather. An independent, agreed weather record is the difference between negotiating and conceding.

The good weather clause

Most performance warranties apply only in "good weather", and the definition varies:

• Maximum wind force (commonly Beaufort 4 or 5)
• Maximum sea state or significant wave height
• No adverse current, or current excluded
• Minimum duration of the good weather period for it to count
• Whose weather data governs — the ship's logs, the charterer's provider, or an agreed independent source

Agree the data source in the charterparty. Disputes where the owner relies on noon reports and the charterer relies on a hindcast provider are decided by whichever the contract names, and when it names neither they are decided slowly and expensively.

Just-in-time arrival

The largest fuel saving available on most voyages is not steaming more efficiently. It is not steaming fast to arrive and wait.

Because power varies roughly with the cube of speed, the fuel needed to cover a fixed distance rises steeply with speed. Arriving four days early to sit at anchor converts that extra fuel into nothing at all — and, under CII, into a worse rating, because fuel is burned while no distance is covered.

The obstacle is commercial, not technical. Under many charterparties the vessel is obliged to proceed with utmost despatch, and berth allocation practices reward early arrival. Virtual arrival and just-in-time schemes address this with an agreed arrival time and a mechanism for sharing the saving.

Practical steps:

1. Include a virtual arrival or JIT clause where the counterparty will accept one
2. Obtain reliable berth availability information before committing to speed
3. Model the fuel saving for each speed option and put the number in front of the commercial team
4. Record the agreement — an informal understanding will not survive a demurrage dispute

Route selection beyond weather

That last row is newly relevant. Voyage classification determines EU ETS and FuelEU treatment, and a route decision changes the compliance cost, not just the fuel cost.

Safety remains the first purpose

Weather routing exists first to keep ships and crews safe. Parametric rolling, synchronous rolling, heavy weather damage, cargo shift and green water on deck remain among the most serious operational hazards, particularly for container ships, car carriers and vessels with deck cargo.

Two rules that should never be traded against efficiency:

• The master's authority to deviate for safety is absolute and must never carry a commercial penalty in practice
• Routing advice is advice; the master decides

Building the capability

1. Contract a routing provider and name them in charterparties where possible
2. Integrate routing data with the vessel performance system so weather correction is automatic
3. Report weather-corrected performance monthly
4. Retain post-voyage weather analysis for every voyage — it is the claims file
5. Train masters and operators on the interaction between speed, arrival timing and CII
6. Review deviations: frequent deviation for weather may indicate a routing or scheduling problem