Relative wave direction restriction for weather matrixes

Overview

Weather-limit matrixes can now restrict operations based on relative wave direction — the direction waves approach a vessel or asset relative to its direction of travel or access point.

This makes it possible to model different operational limits depending on whether waves are following, beam, or head seas.

During simulation, the absolute wave direction from the weather data is converted into a direction relative to a reference direction:

For a moving/route step, the reference direction is derived automatically from the route and represents the vessel's stern direction.
For a stationary step at an infrastructure asset, such as a turbine transfer, the reference is the configured access-point face.
If a relative wave direction restriction is used but no suitable reference direction is available, the relative direction falls back to the absolute wave direction.

The relative direction is represented from 0° to 360°:

0° = following seas
90° = beam seas
180° = head seas
270° = beam seas from the opposite side

Prerequisites

The selected weather data must contain wave direction information.
The operation must have a weather matrix configured.
For stationary operations, an access-point direction should be configured if the restriction needs to be evaluated relative to the asset.
For moving operations, no vessel heading needs to be configured manually; the reference direction is determined from the route automatically.

Where to Find It

Open the relevant process step and its Weather Matrix configuration.

Select Relative wave direction (deg) as one of the matrix inputs, for example the X or Y input.

How to Use It

Open the process step whose weather limits you want to configure.
Open or add a weather matrix.
Select Relative wave direction (deg) as one of the matrix inputs.
Configure the direction ranges and the corresponding weather limits.
For a stationary asset operation, make sure the relevant access-point direction is configured.
Run the case.

For moving operations, the simulation determines the reference direction automatically from the route.

Note: For a weather matrix that uses relative wave direction as an axis, a cell value of 0 is treated as a real zero limit rather than as "no limit." For example, if the cell represents maximum significant wave height, a limit of 0 m means any wave height above 0 m fails the restriction.

Tip: If an asset has multiple access points, the simulation evaluates each available access-point direction and treats the weather as workable if at least one of them complies. This represents choosing a suitable approach based on the current wave direction.

Limitations

If a relative wave direction restriction is used but no route-based or access-point reference direction is available, the relative direction falls back to the absolute wave direction.
The weather data must contain valid wave direction information for the relative-direction calculation to be meaningful.
Wrap-around near the 0°/360° boundary is handled automatically, so no manual adjustment is required.

Frequently Asked Questions

How is the relative angle calculated?

The simulation compares the absolute wave direction — the compass direction the waves are coming from — with the applicable reference direction and normalises the result to the range 0°–360°.

What counts as 0° versus 180°?

0° represents following seas, with waves coming from astern. 90° represents beam seas, and 180° represents head seas, with waves approaching the bow. 270° represents beam seas from the opposite side.

Do I need to configure a vessel heading for a moving operation?

No. For moving operations, the reference direction is determined automatically from the route.

What reference direction is used for a stationary operation?

For a stationary operation at an infrastructure asset, the configured access-point direction is used. If multiple access points are available, each can be evaluated.

Does a 0 value in the matrix mean there is no restriction, like in other weather matrixes?

No. For a matrix using relative wave direction, a cell value of 0 is treated as an actual zero limit.

What happens if no reference direction is available?

The relative wave direction falls back to the absolute wave direction, so the restriction can still be evaluated.