Taming The Weather, The Biggest Obstacle in Maritime.

How voyage planning software can facilitate a dynamic, data-led approach to ensure weather is accounted for in the voyage planning process.

Weather has always been a topic of consuming interest for mariners. Some of the oldest texts in existence describe how the gods were believed to visit seafarers with alternately furious and favourable conditions as they travelled the seas with only the stars to guide them. Today, weather and the challenge of accurately predicting it is still a topic of vital importance in voyage planning. Experts can confidently calculate ocean currents and tides, and navigation with pinpoint accuracy is now commonplace, yet weather remains the wildcard.

Thankfully, modern forecasting techniques based on satellite imagery and continually evolving computer models now offer predictions that are generally accurate, but even these advanced techniques often struggle for precision, especially when attempting to forecast well in advance. For this reason, maritime companies are always seeking the latest and most accurate weather data to manage or adapt voyage plans for the best and safest routes for vessel, cargo, and crew.

Accounting for Uncertainty

Passage planning is no trivial task. For instance, a fully laden vessel performs very differently in rough seas to one in ballast. Container vessels, in particular, experience a dramatic shift in their centre of gravity and increase in windage when laden. It’s also worth noting that the certainty with which assessments can be made varies according to voyage length.

Heavy vessels sit deeply in the water, making them slightly less susceptible to being jostled around by heavy winds and high waves.

A vessel travelling a short coastal shipping route can depart with much higher confidence in the weather forecast than one heading across oceans, simply because a forecast over a few days is far more likely to be accurate than one spanning weeks. The accuracy of forecasts decreases the further ahead you look, and consequently routes must always be adapted to keep voyages within acceptable margins of safety.

Laden vs. Unladen

The question of how a vessel behaves when laden or unladen is a particularly tricky one. When unladen, the vessel can adapt more easily to changing weather conditions. Unburdened by heavy cargo, these vessels can travel more quickly, and by the most efficient route. In this scenario, the vessel operator has considerable latitude to trim the vessel for the expected conditions and may adjust the amount of ballast for anticipated rough weather. On the flip side of this, adjusting ballast is a delicate process that requires precision and manpower. If not done in time, unladen vessels are more susceptible to being jostled around in heavy winds and high waves.

Partially laden vessel can also adapt reasonably well to weather conditions, but one with a full cargo has few options. As such, a laden vessel may have to plan a more conservative route to ensure the safety of its crew and cargo. The risk associated with not doing so and placing vessels in perilous weather conditions is potentially catastrophic.

While all vessels are vulnerable to perilous weather, container vessels have the unique worry of cargo containers being blown from the ship.


Weather considerations inevitably affect scheduling. Ports work to tight timetables and, while a vessel arriving early might be able to wait in the approaches, a late arrival is at best an inconvenience and at worst will completely miss its unloading window. Part of voyage planning, therefore, requires working sufficient flexibility into the schedule to handle any foreseeable weather-related delays and still arrive in time.

Many ports are congested, and therefore only have very narrow windows for when vessels can access berths. If a vessel is shipping perishable goods, waiting can be especially problematic, as each passing moment diminishes the value of the cargo. Inflexible berthing windows also limit the options for early departure, tightening schedules at the outset of the voyage.

Voyage delays caused by weather can greatly affect when vessels will are able to enter ports and access berths to load and unload their cargo.

Where Software Comes In

Bringing all these factors together to create an efficient voyage plan is a challenge. Meteorological services across the world do an outstanding job combining real and predicted data from multiple sources to forecast precipitation, wind strength and direction. There are powerful models that use this information to infer sea states with remarkable accuracy. This information is updated multiple times a day depending on the service, but cannot answer the crucial questions asked by vessel operators: is my vessel, crew, and cargo as safe as possible, and will we meet our deadlines?

Software, such as Passage Manager by OneOcean, is the key to making these voyage planning decisions. The software crunches the weather data to create optimised and viable plans within safety parameters set by the user. For example, OneOcean allows users to create ‘Weather Limits Profiles’ which define safety specifications for wind speed, wave height and minimum distance from storms. These can be set based on the vessel’s laden level, class type and route.

In OneOcean’s Weather module, which is part of Passage Manager, users can enter detailed parametres about their vessel and its thresholds to withstand rough weather so as to generate optimised routes.

Using this information, OneOcean ensures that when routes are created, calculations and risk assessments are as accurate and tailored to the vessel as possible. Better still, the software pulls from live data, and allows route planning to be updated dynamically. Safety considerations are embedded into dynamic passage plans, meaning that as forecasts change, safety risks are recalculated to ensure that exposure is managed. All of this can be monitored by shoreside teams through OneOcean’s FleetManager portal, enabling real-time, informed communication.

The Bottom Line

Weather is always going to be one of the least predictable aspects of maritime operations, but modern forecasting – teamed with cutting edge software such as OneOcean’s voyage planning suite – facilitates an informed, dynamic approach to ensure the safest, most efficient voyage possible.

Get in touch with us today to find out how your organisation can benefit from the most the comprehensive port data available to the maritime industry.

13 September 2021