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Weather Routing

Weather routing is the operational practice of selecting and continuously adjusting a ship’s voyage route based on real-time weather forecasts, vessel-specific performance characteristics and trade-route oceanographic patterns, with the objective of optimising one or more of: fuel consumption, voyage time, cargo motion exposure, crew safety and schedule reliability. Modern commercial weather routing services use numerical weather prediction (NWP) models from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the US National Oceanic and Atmospheric Administration (NOAA) GFS as the primary forecast input, combined with vessel-specific performance polars that map fuel consumption to combinations of speed, draft, wind direction, wave height and period. Typical fuel savings are 2 to 7% on long-distance ocean voyages and 5 to 10% on seasonally challenging routes such as winter North Atlantic, North Pacific or Cape Horn passages. Weather routing is a SEEMP Part III operational measure and contributes directly to annual CII attained improvement, with the saving treated alongside slow steaming, JIT arrival, trim optimisation and hull cleaning in the SEEMP combined operational measures calculator. The principal commercial weather routing service providers are Applied Weather Technology (AWT, US), MeteoGroup Marine (formerly UK Met Office Marine, now part of DTN), StormGeo (Norway, BVS Bon Voyage System), Wärtsilä Voyage Solutions (formerly Eniram), ABS NS Voyage Manager and the emerging Sofar Ocean which uses crowd-sourced ocean buoy data; together these providers serve approximately 80% of the deep-sea commercial fleet through subscription contracts. ShipCalculators.com hosts the principal computational tools: the weather routing fuel savings calculator implements the per-voyage fuel-saving estimation; the weather routing voyage savings calculator provides an alternative parameterisation; the great-circle vs rhumb-line distance calculator compares the geometric routing options; the Pierson-Moskowitz peak period calculator and the Beaufort to Hs conversion calculator provide the underlying wave-statistics inputs. A full listing is available in the calculator catalogue.

Contents

Background and history

Pre-computational weather routing

Practical weather routing has been used since the early days of sail-powered shipping. The classic example is the trade-wind passages developed by Iberian, Dutch, English and French navigators in the 16th to 18th centuries: ships sailing from Europe to the Americas would deliberately route south to capture the NE trade winds, and route north on the return for the westerlies. The American captain Matthew Fontaine Maury’s Wind and Current Charts (1847) and The Physical Geography of the Sea (1855) systematised pre-computational weather routing using compiled logbook observations, demonstrating fuel and time savings of approximately 30% on US East Coast to South America voyages.

In the steam era through the early 20th century, weather routing continued through compiled climate atlases (the Admiralty Weather Reports, the US Naval Hydrographic Office Pilot Charts) and the daily synoptic charts produced by national weather services. Ships used these to plan the broad route shape but had no real-time ability to adjust mid-voyage based on forecast updates.

1950s to 1980s: synoptic-routing service emergence

The first commercial weather routing service was launched by the US Hydrographic Office in the late 1940s for US Navy ships. Commercial shipping followed in the 1950s with services from the US National Weather Service Maritime Branch (later spun out as Oceanroutes in 1972, founded by James Lewis), the British Met Office marine division, and the Japan Meteorological Agency.

These early services operated on a shore-to-ship advisory model: routing experts at the service provider analysed daily synoptic charts and issued routing recommendations to subscribed ships via radio teletype, typically once per 12 to 24 hours. The recommendations balanced weather avoidance (minimising heavy weather) against route-distance economics. The US Coast Guard’s 1979 Weather Routing Effectiveness Study documented average fuel savings of 3 to 5% across the US flag merchant fleet using these services.

1990s: numerical weather prediction integration

The development of numerical weather prediction (NWP) models in the 1980s and 1990s, particularly the ECMWF Integrated Forecasting System (IFS) and the NOAA Global Forecast System (GFS), revolutionised weather routing. Key developments:

  • High-resolution wave forecasting through coupling of NWP atmospheric models with ocean wave models (WaveWatch III, WAM).
  • Ensemble forecasting providing probabilistic uncertainty estimates for routing decisions.
  • Increased forecast horizon: from 3-day reliable forecasts in the 1980s to 7-10 day reliable forecasts by 2000.
  • Vessel performance polars developed by class societies and universities (notably the University of Strathclyde’s marine vehicles research) enabled mathematical optimisation of routes.

The 1995 establishment of Applied Weather Technology (AWT) in California, providing a fully digital ship-to-shore routing service, marked the transition to the modern era of weather routing.

2000s to 2020s: real-time and onboard systems

The 2000s and 2010s saw further evolution:

  • Onboard routing software providing 24/7 routing capability without shore-based latency (e.g. AWT’s Bon Voyage System licensed to StormGeo in 2012, now BVS).
  • Real-time satellite weather data via INMARSAT and Iridium broadband connections.
  • Vessel-specific performance polars built from ISO 19030 standardised hull-and-propeller performance monitoring data.
  • Integration with ECDIS and bridge nautical equipment for one-screen routing display.
  • Integration with shipowner / charterer management systems for fleet-wide optimisation.

By 2020 approximately 80% of the deep-sea commercial fleet was subscribed to some form of commercial weather routing service.

2020 onwards: AI-augmented routing

The 2020 to 2024 period has seen the emergence of AI-augmented routing using machine learning to optimise the multi-objective routing problem. AI techniques are particularly useful for:

  • Improving the vessel performance polar by learning from actual operational data rather than published shop tests.
  • Predicting probability of cargo damage under different routing options.
  • Optimising fleet-wide routing considering port congestion, cargo readiness and onward logistics.

The leading AI routing vendors include AWT, StormGeo, Wärtsilä Voyage Solutions (with the Eniram acquisition), ABS NS Voyage Manager and emerging entrants including Maersk Routing (in-house), Cargill Ocean Transportation Routing (in-house), Hellesøe Routing (Danish startup) and Sofar Ocean (US ocean-data startup).

Methodology

Numerical weather prediction inputs

Modern weather routing depends on global NWP models providing forecasts on a regular grid:

  • ECMWF IFS (European Centre for Medium-Range Weather Forecasts): the global gold standard, run twice daily with 9-day forecast horizon at 0.1° resolution.
  • NOAA GFS (Global Forecast System): the US public-domain model, run four times daily at 0.25° resolution.
  • NOAA WaveWatch III: ocean-wave forecasting coupled with GFS.
  • ECMWF Wave Model (WAM): wave forecasting coupled with IFS.
  • HYCOM (Hybrid Coordinate Ocean Model): operational ocean model providing currents.
  • ETOPO (Earth Topography): bathymetry for shallow-water routing.

The forecast data is downloaded via the WMO Global Telecommunications System (GTS) by routing service providers, processed onto vessel-specific routing grids, and refined for marine conditions.

Vessel performance polars

A vessel performance polar is a tabular or functional description of the ship’s fuel consumption as a function of:

  • Service speed (typically 4 to 25 knots).
  • Draft (laden vs ballast vs partial load).
  • Wave height (Hs): significant wave height in metres.
  • Wave period (Tp): peak wave period in seconds.
  • Wave direction relative to ship: bow, beam, quarter, stern seas.
  • Wind speed and direction: similar.
  • Hull condition: clean vs partially fouled vs heavily fouled.
  • Trim: optimum trim or fixed trim.

The polar is typically constructed from a combination of:

  • Sea trial data (ISO 15016 standardised conditions; corrected to standard conditions).
  • Operational data from past voyages (ISO 19030 hull-and-propeller performance monitoring).
  • CFD (Computational Fluid Dynamics) simulations for conditions outside the empirical envelope.

The performance polar is the critical input that distinguishes weather routing services: better polars produce better routing recommendations.

Routing optimisation algorithms

The classic weather routing problem is a multi-objective optimisation with the following objectives:

  • Minimise voyage fuel consumption (the primary objective for most operators).
  • Meet ETA target (avoid lateness penalty under charter party).
  • Minimise cargo motion exposure (avoid heavy roll, pitch, slamming).
  • Maintain crew safety (avoid storm conditions exceeding crew limits).

The principal optimisation algorithms used:

  • Isochrone method (James 1957): tracks the locus of points reachable within a given time; iteratively expands; selects the best route from the Pareto frontier. Computationally efficient, suitable for shore-to-ship advisory services.
  • Dynamic programming (Bellman 1957): discretises the route space and finds the global optimum through backward induction. Computationally heavier but produces globally optimal routes.
  • Genetic algorithms: stochastic optimisation suitable for complex multi-objective formulations.
  • Machine learning: trained on historical routing decisions to suggest routes that match human-expert behaviour.

Most modern commercial services use a combination of these algorithms, with isochrone or dynamic programming providing the deterministic backbone and machine learning enhancing the decision quality.

Forecast uncertainty handling

Weather forecasts have intrinsic uncertainty that grows with forecast horizon:

  • 3-day forecast: typical wave-height uncertainty ±0.5 m (good).
  • 5-day forecast: ±1.0 m (moderate).
  • 7-day forecast: ±1.5 m (poor).
  • 10-day forecast: ±2.0 m (effectively unusable for tactical decisions).

Modern routing services handle this through:

  • Ensemble forecasting: running multiple NWP forecasts with perturbed initial conditions to estimate uncertainty.
  • Adaptive routing: re-running the routing optimisation as new forecasts arrive (typically every 6 to 12 hours).
  • Risk-adjusted routing: using the route with the lowest expected fuel consumption rather than the lowest deterministic fuel consumption.

Performance and economics

Real-world fuel savings

Reported fuel savings from commercial weather routing services:

Trade routeVoyage typeTypical fuel saving
Asia to US East Coast (via Panama)Container3 to 5%
Asia to Europe (via Suez)Container3 to 5%
North Atlantic (Europe to US East Coast)Container4 to 8%
Middle East to East AsiaCrude oil VLCC2 to 4%
Cape Horn (South America to Asia)Bulk carrier5 to 10%
Winter North AtlanticBulk carrier5 to 10%
Indian Ocean monsoon (June-Sep)Various3 to 7%
MediterraneanCruise / ferry1 to 3%

The savings vary significantly with:

  • Trade-route weather variability: routes with consistent weather (Caribbean, Mediterranean) achieve smaller savings; routes with variable weather (North Atlantic, North Pacific) achieve larger.
  • Vessel performance polar quality: ships with detailed polars (bulk, tanker, container) achieve better routing than ships with limited polars (cruise, RoRo where polar is less critical to fuel cost).
  • Routing service quality: top-tier services (AWT, StormGeo) typically achieve 1 to 2 percentage points better than lower-tier services.

Capital and operational cost

Weather routing is essentially a subscription service:

  • Fleet subscription: USD 5,000 to USD 50,000 per ship per year, depending on service level and number of ships.
  • Per-voyage subscription: USD 500 to USD 2,500 per voyage (less common; mostly for spot-charter operators).
  • Onboard software licence: USD 3,000 to USD 25,000 per ship per year (e.g. StormGeo BVS, AWT BonVoyage).
  • Crew training: minimal; bridge teams are familiar with routing principles.

The annual fuel saving (for a typical container ship consuming 30,000 t/yr at USD 600/t) of 3 to 5% = USD 540,000 to USD 900,000.

The payback period is therefore essentially immediate (less than 1 month). Weather routing has been the lowest-cost decarbonisation lever available for decades.

CII improvement

A 3 to 5% per-voyage saving translates into approximately the same improvement in annual CII attained:

  • For a bulk carrier with attained CII of 5.5 (D rating, 10% above Required), a 4% routing improvement brings attained CII to ~5.28 (still D but closer to C boundary).
  • Combined with slow steaming (10%), JIT arrival (4%) and hull cleaning (5%), the combined improvement is approximately 21% (using the non-overlapping multiplicative formula).

Notable deployments

Maersk routing

Maersk operates one of the largest in-house weather routing capabilities, with a dedicated routing centre at the company’s Copenhagen HQ. The centre:

  • Provides routing for the entire Maersk container fleet (~700 vessels by 2024).
  • Integrates with Maersk’s onboard performance monitoring.
  • Reports approximately 5 to 7% average annual fuel saving across the fleet.
  • Has been credited with approximately USD 200 million annual fuel cost savings.

Cargill Ocean Transportation routing

Cargill as the world’s largest dry bulk cargo buyer operates an in-house routing capability for chartered vessels:

  • Partnership with AWT for technical routing services.
  • Integrates with Sea Cargo Charter reporting.
  • Reports 4 to 7% fuel savings on Atlantic and Pacific bulk carrier voyages.
  • Uses the savings to support the Sea Cargo Charter alignment reporting.

StormGeo BVS deployment

The StormGeo BVS (Bon Voyage System) is the most widely-used commercial routing service, with approximately 9,000 vessel subscriptions globally:

  • Acquired from AWT in 2012.
  • Significantly enhanced with cloud-based forecast updates from 2018.
  • Integration with Wärtsilä Voyage Solutions from 2024.
  • Reports average 4 to 6% fuel savings across subscribed vessels.

COSCO Shipping routing

COSCO Shipping (the Chinese state-owned shipping conglomerate) operates an in-house routing capability for the COSCO container, bulk and tanker fleet:

  • Partnership with Chinese state weather service (China Meteorological Administration).
  • Approximately 1,000 vessels routed.
  • Reports 3 to 5% fuel savings.

Weather routing combines naturally with several other operational measures:

Slow steaming

Slow steaming reduces vessel speed below design speed for fuel efficiency. Combined with weather routing, the optimum route can be re-calculated for the slower target speed, often producing further savings (the slower vessel can take more advantageous routes that would be sub-optimal at high speed).

Just-In-Time arrival

JIT arrival coordinates port arrival to avoid anchor wait. Combined with weather routing, the routing service can optimise speed to arrive at JIT-precise times while still routing around weather.

Trim optimisation

Trim optimisation adjusts the ship’s longitudinal trim to minimise resistance. Combined with weather routing, the trim can be adjusted dynamically based on the expected sea conditions on each voyage segment.

Hull cleaning

Regular hull cleaning maintains the vessel performance polar at “clean” rather than “fouled” levels. Weather routing assumes the ship is at its baseline polar; degraded polars produce lower routing benefits.

The SEEMP combined operational measures calculator implements the combined effect using the standard non-overlapping multiplicative formula.

Safety considerations

Weather routing has critical safety implications beyond fuel optimisation:

Heavy weather avoidance

Weather routing routinely avoids ships from being caught in:

  • Tropical cyclones (typhoons, hurricanes, cyclones): IMO Resolution A.893(21) on Voyage Planning explicitly references avoidance of tropical-storm tracks.
  • Extra-tropical depressions (winter North Atlantic, North Pacific): typically Beaufort 9-12 conditions exceeding most vessel design limits.
  • Polar lows and Mediterranean low: smaller-scale intense storms.
  • Squalls associated with the inter-tropical convergence zone.

The IMO and major flag states explicitly recommend the use of weather routing for voyage planning under SOLAS Chapter V Regulation 34 (passage planning).

Parametric rolling avoidance

Some container ships are susceptible to parametric rolling, a dangerous resonance condition that occurs when wave encounter period matches twice the ship’s roll period. Modern weather routing services include parametric-rolling-avoidance algorithms that route the ship away from the encounter wave conditions.

Cargo motion damage

For cargoes susceptible to motion damage (project cargo, vehicles, refrigerated cargo, sensitive industrial equipment), weather routing optimises for minimum motion exposure rather than minimum fuel. The trade-off is typically 1 to 3% additional fuel cost in exchange for substantial reduction in cargo damage claims.

Crew safety

Beaufort 8+ conditions present risks to crew (particularly during deck operations, maintenance and lifeboat drills). Weather routing reduces crew exposure to severe weather, contributing to safety performance metrics tracked by P&I clubs and operator HSE departments.

Future outlook

By 2030 weather routing is expected to:

  • Cover approximately 95% of deep-sea commercial fleet (vs ~80% in 2024).
  • Achieve average 4 to 6% per-voyage fuel savings (vs ~3 to 4% currently) through improved vessel performance polars and AI-augmented routing.
  • Be increasingly integrated with JIT arrival through digital port-coordination platforms.
  • Be increasingly integrated with Sea Cargo Charter and Poseidon Principles reporting through standardised data interfaces.

By 2040 weather routing combined with autonomous routing decisions (subject to MASS regulatory framework progress at the IMO) is expected to enable continuous re-routing without human-in-the-loop latency, achieving an additional 1 to 2 percentage points of fuel savings.

See also

References

  1. International Standards Organisation. ISO 19030:2016 - Ships and marine technology - Measurement of changes in hull and propeller performance. ISO, Geneva, 2016.
  2. International Standards Organisation. ISO 15016:2015 - Ships and marine technology - Guidelines for the assessment of speed and power performance by analysis of speed trial data. ISO, Geneva, 2015.
  3. IMO Resolution A.893(21). Guidelines for Voyage Planning. IMO, 25 November 1999.
  4. James, R.W. A New Method of Determining Optimum Tracks for Ship Routing. Memo, Naval Hydrographic Office, 1957.
  5. Bellman, R. Dynamic Programming. Princeton University Press, 1957.
  6. Maury, M.F. The Physical Geography of the Sea. Harper, 1855.
  7. ECMWF. Integrated Forecasting System Documentation, Cycle CY49R1. ECMWF, Reading, 2024.
  8. NOAA. Global Forecast System (GFS) Documentation. NOAA / NCEP, 2024.
  9. Applied Weather Technology. Annual Routing Service Report 2024. AWT, Sunnyvale CA, 2024.
  10. StormGeo. BVS Annual Report 2024. StormGeo, Bergen, 2024.
  11. MeteoGroup / DTN. Marine Routing Annual Report 2024. DTN, Minneapolis, 2024.
  12. Wartsila Voyage Solutions. Annual Report 2024. Wartsila, Helsinki, 2024.
  13. Sofar Ocean. Annual Report 2024 - Marine Sector. Sofar Ocean, San Francisco, 2024.
  14. Cargill. Ocean Transportation Annual Report 2024. Cargill, Geneva, 2024.
  15. DNV. Maritime Forecast to 2050 - Operational Efficiency Section. DNV, Oslo, 2025 edition.
  16. Lloyd’s Register. Weather Routing: Practical Implementation Guide. Lloyd’s Register Marine, London, 2024.

Further reading

  • IMO Marine Environment Division. Voyage Planning and Weather Routing Guidance. IMO, 2018.
  • DNV. Maritime Forecast to 2050. DNV, Oslo, 2025 edition.
  • Lloyd’s Register. Performance Management of Marine Vessels. Lloyd’s Register Marine, London, 2023.