Case Study: Vessel Roll Causes Fall, Shoulder Fractures and Dislocates

The OOW was undertaking his usual duties at sea in heavy weather. At one point the vessel rolled even more than usual. The OOW was standing near the chart table, then suddenly lost his balance and fell on the deck, heavily impacting his left shoulder.

He required first aid and medication and was placed on light duties until arrival at the next port. After an examination at the local hospital it was discovered he had fractured and dislocated his left shoulder.

The official report’s conclusions included, among others:

The first vessel dragged anchor because insufficient anchor cable had been deployed for the tidal range and environmental conditions.
The vessel’s OOW did not immediately recognise the ship was dragging its anchor because the anchor position monitoring interval was not appropriate.
The vessel was unable to manoeuvre quickly because its engines were not in immediate readiness.

Lessons learned

Anchor watch needs your undivided attention.
Several methods can be used to calculate the necessary scope of cable needed when anchoring including (where Wd is water depth in metres): number of shackles of cable = 1.5√ (Wd), or length of cable in metres = 6 to 10 × (Wd).
Water depth to draught ratio (Wd/D) is an important factor to consider when anchoring in strong currents. Smaller ratios will cause greater forces to act on the hull; this may cause the vessel to drag anchor at low water even though all was fine at high water.
Factors such as the strength of the wind and tidal stream, tidal range, nature of the seabed, sea conditions, vessel loading, the extent of safe.

Water available and duration of stay must also be considered when anchoring.

Reference: nautinst.org