Wednesday, July 14, 2010

Ro/Ro Vessels dificulties in wind underway and at anchor

A 200 meter long  PCTC upbound Westerschelde River (photo by K.C.)

From: The Nautical Institute Marine Accident Reporting Scheme MARS Report No 190 August 2008

Ro-ro ships – manoeuvring difficulties

An inbound pure car and truck carrier (PCTC) was approaching the pilot station at her scheduled time, in very confined waters. A gale warning was in force and with only two miles to go to the pilot embarkation point, the wind suddenly increased and pilotage services were abruptly suspended.

The master was instructed to await further orders and decided to head back to open waters rather than wait in the confined area or anchor there. The wind caught the beam of the high-freeboard and low draught vessel, and started setting her on to the lee shore, less than two miles downwind. Using full rudder and engine power, and transmitting appropriate signals on the air horn and VHF radio, the master just managed to turn the ship’s head into the wind and execute the 180-degree turn and head out to open sea.

Once out of the lee of the land, the full force of the gale caused the ship to move sideways at about five knots, even with the engine going on harbour full ahead. The vessel remained stubbornly beam on to the wind despite all attempts to heave to with the head into the sea and swell. This type of vessel has been rightly described as a ‘ping-pong ball on the water’ and under high wind conditions, ro-ros are almost impossible to control or manoeuvre.

At the first indication of approaching strong winds, masters of ro-ros and similar high-sided vessels must not hesitate to leave port or confined waters and anchorages and head out to open sea. Maintaining a safe position under way in the lee of a high offshore island is a safe option, provided the location and predicted movement of the weather system is known.

If sailing from port is not possible, ships have been kept alongside with continuous use of tugs, and, in uncrowded anchorages, mooring to two bower anchors may considered, but with engines in full readiness until the wind has abated.

Even with full scope of chain on both anchors, ro-ro vessels tend to yaw violently in strong winds and the ‘jerk’ at the extremity of each yaw may cause the anchors to drag, especially if the holding ground is less than ideal.

Mariners whose vessels may be navigating or lying at anchor near a ro-ro vessel in high winds, must allow for a greater margin of safety.

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