A merchant vessel is said to be having a “dragging anchor” when the vessel drifts without holding power inspite of being anchored. Dragging anchor has been the reason for several accidents such as collision, grounding, or stranding.
Merchant vessels stay at anchorage for various reasons:
Waiting for berthing prospectus
Cargo discharge and loading
For carrying out maintenance , hatch cleaning
Waiting for Instructions from owners or charters
Quarantine etc.
The main reason for a vessel dragging its anchor is because of rough weather conditions. In such situations, it is extremely important for seafarers to collect all necessary information to familiarise with the situation and prevent dragging of anchor as much as possible. Some important parameters that needs to be considered are:
Prevailing weather condition of that particular area
Safe position for anchoring the vessel
Wind and tidal behaviour of that area
Contact information of port authorities in case of assistance required etc.
At most ports, it is inevitable for a vessel to wait at anchorage and the time at anchorage can be for days or even weeks. During such times, the master and ship crew should identify possible dangers to the ship and make all the necessary preparations.
A vessel dragging anchor is a threat to its own and also to other vessels in the vicinity, often leading to an emergency situation such as collision, grounding or stranding, depending on the manoeuvrable condition of the ship.
In such situations, a quick assessment of the situation can only be achieved by a vigilant bridge watch, contingency plan to tackle any emergency, quick response and good judgment of the situation. It may take some time to weigh the anchor and restore the vessel to its full manoeuvrable condition, but no serious accident should happen if there is enough sea room and time to do so.
Following points should be considered by a seafarer prior anchoring where dragging anchor is predicated:
Take on heavy weather ballast, taking in to account the stability of the vessel and depth of water below the keel
Pay out more anchor cable depending on the size of the vessel and weather condition
Keep a safe distance from other anchored ships, shoals and other dangers, leaving room for manoeuvring
Weigh anchor and shift the vessel to different position away from the vicinity of other vessels, provided prior permission is received from VTS of that area, port authorities and owner’s orders
Increase the efficiency of the bridge team by adding an extra lookout
Keep the main engines standby for manoeuvrability
How to assess the vessel is dragging its anchor?
Check the ship’s position at frequent intervals, to confirm if the vessel is outside the swinging circle. Use all available means, both visual and electronic equipment such as GPS, RADAR and ECDIS, to make the appraisal of the situation. If the vessel deviates from the circle, it is likely to be dragging its anchor
The bow cannot stand against the wind
Check anchor chains for slipping, a small pole with a cloth as flag like arrangement can be tied to the links to understand the slipping of anchor chains
Extra vibration and weight on anchor cable
Check the speed over ground (SOG) when the vessel is swinging, the SOG can increase variably and this should not be misinterpreted
Check the course recorder for figure of eight motion locus
Also monitor the position and distance of vessels nearby. In case if they are dragging counter measures to be taken to safe guard own vessel
What actions to be taken if the vessel has started dragging anchor?
Master to be informed, do not hesitate to call him at any time of the day, his experience and decision making authority is vital in any give situation
Inform engine room and start the main engine with the permission from the master and give power to windlass if it is not already given. Make the vessel ready for manoeuvring
Stop all cargo operations and prepare vessel for manoeuvring. Let go cargo barges and crane barges if they are alongside
Inform and alert Vessel traffic system (VTS) and other vessels nearby about the condition and inform about the actions taken. Seek permission for re-anchoring
Start heaving up the anchor and once the vessel’s manoeuvrability is restored, shift the anchorage position where drifting can be safer or take to the open sea
Deploy more cablse or drop a second anchor (not recommended for big vessels) before the speed of dragging of the vessel increases. This can stop the small vessel from dragging anchor at very early stage before the ship is pressed to leeward side with increasing speed
Use bow thrusters, main engine and steering to manoeuvre. It becomes more difficult to weigh anchor when the vessel is pressed more to the leeward side and takes considerable amount of time. Use bow thrusters for stemming the wind. Do not override the anchor especially in shallow waters as the vessel may impact on the anchor during pitching.
If the scenario permits, let the vessel drag in a controlled manner. But this is not recommended in areas where offshore work such as oil and gas operations are being carried out, which can result in damaging the submerged pipe lines, cables etc.
Release the bitter end and let go the anchor completely, when weighing of anchor is not possible. A ship without minimum of 2 anchors is not considered to be sea worthy, a careful assessment is to be made prior making this decision
Call (tugs) for assistance. This is possible only if the weather permits
Most accidents collision or grounding happens while the vessel is at anchor mainly because of no early prediction of dragging anchor. Time plays a vital role in area of high vessel density and this time lapse results in difficulty in restoring the manoeuvrability of the vessel. Ensure that proper contingency plan is set in place to control such incidents and avoid arising of any emergency due to dragging anchor.
