WATCHOUT Insufficient focus on effects of squat caused ferry to ground

01 Feb 2021 The Navigator

In this series, we take a look at maritime accident reports and the lessons that can be learned

What happened?
A roll on-roll off freight ferry grounded in conditions of good visibility, shortly after setting off on its voyage. The bridge team heard a loud noise and felt a shuddering vibration for around seven seconds. Propulsion and steering were not affected, so the vessel was able to set off again quite quickly. However, the ferry soon started showing a sevendegree list to port and was brought back to port. There, it was discovered that a port-side heeling tank and void space had been breached during the grounding. The ferry was taken out of service for three weeks while the damage was repaired.

During investigations, it became clear that the bridge team on the ferry had not considered the effects of squat adequately during their passage planning and had not allowed sufficient UKC given the state of the tide. In addition, the electronic navigation system was not being used effectively to spot potential areas of grounding or to help calculate a safer level of UKC. The ferry’s onboard procedures specifically stated that the Master was obliged to be aware of the effects of squat (including channel and vessel widths), sea conditions (including swells) and how these could affect the ship’s handling, UKC and speed. These aspects were not covered in enough detail during planning, leading directly to the grounding incident.

Why did it happen?

  • The bridge team did not consider the effects of squat properly during passage planning prior to the journey.
  • One of the vessel’s previous Masters had produced a ready reckoner to assist with passage planning. This advised that, when leaving on a flooding tide with a draught of 5.5m, a minimum height of tide of 1.3m on the harbour gauge was required. The ready reckoner did not allow for the potential decrease in UKC due to squat.
  • The ferry’s planned course brought it straight into the area where it grounded, due to UKC calculations not being sufficient.
  • The electronic navigation system was not being used to its full potential, meaning that the bridge team did not benefit from an early enough warning to avoid the impending grounding.

 What changes have been made?

  • The ferry company has taken steps to raise awareness amongst its employees around dealing with shallow water, the effects of squat and effective passage planning.
  • Onboard procedures documentation has been revised to highlight the potential for squat and interaction in pilotage waters when determining speed and UKC.
  • The company has also enhanced its overall bridge resource management training and electronic navigational systems.


The Nautical Institute’s Mariners’ Alerting and Reporting Scheme (MARS) - - comprises a fully searchable database of incident reports and lessons, updated every month. If you have witnessed an accident or seen a problem, email Captain Paul Drouin at and help others learn from your experience. All reports are confidential – we will never identify you or your ship.