Why Do Ships Change Their Routes?

Here are some common reasons that force a ship to change its direction.

1. Bad Weather Can Force Ships to Change Course

Weather is one of the most common reasons for a route change. Large ships can travel through many types of weather, but severe storms, strong winds, high waves, and tropical cyclones can make a planned route unsafe or inefficient.

A captain may choose to:

• Move around a storm
• Slow down
• Change heading
• Wait in a safer area
• Take a longer route

The IMO recognizes weather routing as a way of providing ships with suitable routes that help them avoid bad weather and improve safety.

How can you see this on MarineRadar?

If you are tracking a vessel during bad weather, look for a combination of:

Sudden course change + reduced speed + longer route

Together, these can suggest that the vessel is responding to changing conditions. Our guide to using MarineRadar’s Weather Map explains how to compare weather overlays with a vessel’s position and movement.

However, AIS tracking alone cannot tell you the exact reason for every maneuver. A route change should therefore be treated as an observation rather than proof of a specific event.

2. Ships May Avoid Dangerous or High-Risk Areas

Safety is another major reason for rerouting.

Ships may avoid areas affected by:

• Armed conflict
• Security threats
• Piracy risks
• Maritime incidents
• Temporary navigation restrictions
• Environmental hazards

Recent global events provide a clear example.

UNCTAD reported that disruptions in the Red Sea caused many container ships to avoid the Suez Canal and take longer routes around the Cape of Good Hope. In early 2024, hundreds of container vessels had already been rerouted. For a later development affecting this corridor, see our September 10, 2026 report on Mokha port and the threat to Bab al-Mandab shipping.

A longer route can actually be the safer route.

A straight line is not always the best route.

A shipping company may accept:

• More distance
• More fuel consumption
• Longer voyage time

3. Port Congestion Can Change a Ship’s Journey

A vessel may reach the area around its destination but still change its movement because the port may be busy.

Large ports can experience:

• Long vessel queues
• Limited berth availability
• Anchorage congestion
• Delayed cargo operations
• Weather-related closures
• Pilot or tug availability issues

Instead of entering immediately, a vessel may remain offshore or move to an anchorage.

On MarineRadar, you may notice:

• Very low speed
• Repeated movement around an area
• A vessel remaining offshore
• Changes in ETA
• Several ships clustered near a port

This does not necessarily mean the ship has changed its final destination. It may simply be waiting for an available berth or suitable conditions.

4. Traffic Separation Schemes Influence Ship Routes

Ships cannot simply travel wherever they want. Busy maritime areas often have organized traffic systems.

These can include:

• Traffic separation schemes
• Traffic lanes
• Two-way routes
• Recommended tracks
• Deep-water routes
• Precautionary areas
• Areas to be avoided

The IMO lists these as established routing measures used to improve navigation safety and manage vessel traffic.

5. Water Depth Can Affect the Route

A ship’s size matters. Large vessels may have a considerable draft, meaning they sit deep in the water. They sit deep in every shallow area. Instead, they may need to follow deeper routes.

This is one reason a vessel may appear to make a strange detour around an island, coastline, or shallow-water region. The route may be longer, but the available water depth makes it safer.

6. Canals and Chokepoints Can Change Global Routes

Some waterways are extremely important to international shipping.

Examples include:

• Suez Canal
• Panama Canal
• Strait of Hormuz
• Other major straits and narrow passages

When one of these locations faces restrictions or disruption, shipping companies may need to find alternatives.

A canal closure or restriction can therefore turn a relatively short voyage into a much longer ocean journey.

Example: Suez Canal vs. Cape of Good Hope

A ship traveling between Asia and Europe may normally use the Suez Canal.

If the Red Sea route becomes unsuitable, the vessel may instead sail around southern Africa.

That creates:

Longer distance → longer voyage → higher fuel use → possible ETA changes

UNCTAD’s latest maritime transport review reported that ships rerouted around the Cape of Good Hope, contributing to longer distances, higher costs, and increased emissions.

7. Fuel Efficiency Can Influence Route Decisions

Distance is not the only thing shipping companies consider. Fuel consumption matters too.

A route that looks shorter may not always be the most efficient option. Currents, weather, vessel speed, traffic, and operating conditions can influence fuel consumption.

Ships may therefore adjust:

• Speed
• Course
• Waypoints
• Route length

Sometimes a vessel may travel slightly farther to achieve better operational efficiency.

This is particularly important for large commercial ships because even small efficiency improvements can matter over long voyages.

8. Port Schedules and Commercial Decisions Matter

Ships operate as part of larger logistics networks.

A route is connected to:

• Cargo schedules
• Connecting vessels
• Port appointments
• Customer deliveries
• Bunkering
• Maintenance
• Crew schedules

If the destination port becomes unavailable or the schedule changes, the vessel’s voyage may also change.

9. Environmental Rules Can Affect Ship Movement

Environmental protection is another factor. Some marine areas are environmentally sensitive or have navigation restrictions.

The IMO’s routing framework includes areas to be avoided where exceptional danger or sensitive ecological and environmental factors justify such measures.

As a result, vessels may need to navigate around certain areas rather than take the shortest possible path.