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Relative wave direction restriction for weather matrixes

Overview

Weather-limit matrixes can now restrict operations based on relative wave direction — the direction waves hit a vessel or asset relative to its heading or access point — rather than only the absolute compass direction. This reflects that vessels typically tolerate larger waves from astern (following seas) than from the bow (head seas) or the side (beam seas).

At runtime, the simulation converts the absolute wave direction from the weather data into an angle relative to a reference direction:

  • For a moving/route step, the reference is the stern (opposite the direction of travel).
  • For a stationary step at an infrastructure asset (e.g. a turbine transfer), the reference is the configured access-point face.
  • If no heading is known, or the restriction isn't set to relative mode, the criterion falls back to the absolute wave direction, as before.

0° corresponds to following seas, 90° to beam seas, and 180° to head seas.

Prerequisites

  • A weather matrix must already exist in the case configuration.
  • To get a meaningful relative-direction result, the relevant vessel or asset should have a known heading or access-point face configured.

Where to Find It

Design → case configuration → weather matrix setup → wave direction restriction type.

How to Use It

  1. Open the weather matrix you want to configure.
  2. Set the wave direction restriction type to relative.
  3. Confirm the vessel heading or access-point face is configured, so the simulation has a reference direction to calculate against.
  4. Run the case.

Note: For a relative wave direction matrix, a cell value of 0 is a genuine limit of zero (no operation allowed at that relative angle). This is different from other weather matrixes, where a 0 cell means "no limit."

Tip: If an asset has multiple access points, the simulation checks each candidate reference direction and treats the weather as workable if at least one access point complies — modelling the vessel choosing the most sheltered approach.

Limitations

  • If no heading or access-point face is known for a step, the restriction falls back to using the absolute wave direction instead of a relative one.
  • Wrap-around near the 0°/360° boundary is handled automatically, so no manual adjustment is needed near that boundary.

Frequently Asked Questions

How is the relative angle calculated? The relative wave direction is the absolute wave direction (the compass direction the waves are coming from) minus the reference direction, normalised to 0–359°.

What counts as 0° versus 180°? 0° is following seas (waves from astern), 90° is beam seas, and 180° is head seas (waves on the bow).

Does a 0 value in the matrix mean there's no restriction, like in other weather matrixes? No — for relative wave direction matrixes specifically, a 0 value means a real limit of zero. This is the opposite of the convention used in other weather matrixes.

What happens if the vessel's heading isn't known? The restriction falls back to using the absolute wave direction, the same way it worked before this feature was introduced.