Why route and speed must be optimized together

Weather routing has traditionally been associated with one question:

Which route should the vessel take?

It is an important question, but it is only half of the optimization problem.

A vessel does not simply travel along a line at a fixed speed. Its performance changes continuously with waves, wind, currents, water depth and the power available from the main engine.

That means a truly optimized voyage has to consider both where the vessel sails and how it operates along the way.

A shorter route is not always the better route

The shortest geographical route between two ports may look attractive on paper.

But if that route takes the vessel through adverse currents or heavy head seas, the additional resistance may reduce speed and increase fuel consumption considerably.

A slightly longer route through more favourable conditions can therefore produce a better overall result.

The opposite can also be true. Avoiding every area of poor weather with a large geographical deviation may add so much distance that the alternative becomes less efficient.

The challenge is therefore not simply to avoid bad weather.

It is to understand the complete commercial and operational consequence of each alternative.

Speed cannot be separated from weather

There is another important part of the equation.

A vessel instructed to maintain a certain speed in calm water may not be physically capable of maintaining the same speed in severe weather without significantly increasing engine load.

This is why treating vessel speed as a fixed number throughout an optimization can create an unrealistic picture of the voyage.

In practice, speed responds to the conditions the vessel encounters.

Available engine power, waves, wind, currents and shallow-water effects all influence the speed that can realistically be achieved at any given point.

A good voyage simulation needs to reflect this.

Sometimes the best route is a change in speed

Consider a vessel approaching a weather system.

One option is to make a substantial deviation around it.

Another may be to reduce engine load temporarily, allow the weather system to pass, and then increase power again afterwards.

Depending on the vessel, weather and required arrival time, the second option may use less fuel while maintaining the same ETA.

In many cases, the optimum solution is a combination of both:

• A change to the geographical route
• A change to the engine or speed profile
• Continuous consideration of the weather encountered along the voyage

This is why route optimization and speed optimization should not be treated as separate exercises.

The commercial objective matters

There is also no single definition of an optimum voyage.

A vessel operating against charterparty consumption figures has a different objective from a vessel that must arrive at a fixed ETA.

A vessel with flexibility in its arrival time creates another optimization problem entirely.

For one voyage, the priority may be fuel consumption.

For another, it may be maintaining an ETA.

For another, the best commercial result may come from balancing fuel consumption against the cost of time to determine the most economical arrival.

The route, engine profile and weather therefore have to be evaluated against the actual objective of the voyage.

Repeating the calculation as conditions change

The optimum answer also changes.

Weather forecasts develop. Currents change. The vessel may not follow yesterday's route exactly. Its position changes continuously.

For that reason, voyage optimization should not be viewed as a calculation performed once before departure.

At Optimum Voyage, the remaining voyage is re-optimized regularly using the latest vessel position and weather information.

The purpose is simple: the advice should reflect the voyage the vessel is actually sailing, not the voyage that was expected several days ago.

One voyage, one connected problem

Route, speed, weather and commercial objectives all interact.

Optimizing one while holding the others artificially fixed can leave significant potential unused.

Our approach is therefore to treat the voyage as one connected optimization problem.

The technology may be complex behind the scenes.

For the operator and Master, the objective is much simpler:

A safe, navigable and commercially optimized voyage based on the conditions the vessel is actually expected to encounter.