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Safe anchoring - planning and operational guidance for cargo ships

Anchoring is a critical shipboard operation.There are a number of reasons why a vessel may wish to anchor, for example:
  1. the berth or cargo is not available
  2. an amendment to the passage plan
  3. the pilot is not available / boarding delayed
  4. machinery breakdown
  5. awaiting good weather / adverse weather
  6. voyage orders not available.
Anchoring operations are planning consists of information, instructions, and actions that contribute to a procedure for maneuvering the vessel to the designated anchor position and successfully anchoring in a safe, seamanlike manner taking the prevailing weather conditions and sea state into consideration. Improper anchoring has a consequence. The ship may get into colliding with other vessels, or she may run aground and cause damage to property and environment. It is, therefore, for the best interest of all concerned anchoring should be done safely. Proper planning and teamwork are the basis for a safe anchoring operation. The Master should brief the personnel involved with the planned anchoring operation and update the engine room accordingly.



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Oil Tanker Safety Guide
Typical persons attending the briefing include:
Maintaining a safe operation All checks, inspections, and calculations as per the Arrival Checklist must be completed in a timely fashion to avoid interfering with a smooth, planned approach. A suitable risk management system must comply. Keep the engine room fully advised of the vessel's progress, especially when entering: shallow water, high-risk areas, restricted or confined waters.

As far as circumstances permit, maintain excellent communication with the Port Authority and Vessel Traffic Services (VTS). Request any information regarding shipping movements that could affect the vessel's safe progress to the anchor position. The vessel will now proceed to the designated anchor position and anchor as per planned method.

anchoring terms
Fig: Anchoring terms

Clearing the anchor(s) for arrival
Always be alert to any changing circumstances e.g., excessive vibration or unusual noise of machinery.

Once the planned length of the chain is in the water, the guillotine bar should be dropped and secured, and the chain allowed to bear against the guillotine bar. The guillotine bar is designed to take the weight of the anchor cable.

The Windlass should be out of gear, and the brake applied. Throughout anchor period the appropriate anchor signals are to be used (ball, lights, bell, and gong).

During an anchoring operation the following factors should be considered:
Preparing and lowering the anchor: When the anchor party has been briefed, the Officer in charge will first establish communication with the Bridge before proceeding forward.
Before arrival at or off the port, both anchors are to be cleared ready for use. Anchors should only be cleared when the water depth will allow recovery of the anchor and cable if they are accidentally let go. An anchor marking buoy is to be available and ready for use.

Visual Inspection: Before clearing the anchors, a visual inspection, as far as possible, should be conducted of the anchoring system. The visual inspection may include: Under the direct supervision of the Officer in charge, the procedure for preparing and lowering the anchors can be completed. Particular care must be taken when the weight of the cable is secured by the windlass brake only. The anchor party must be alert to any changing circumstances.

Arriving at the anchoring position: Before anchoring, the direction and speed of the current or tidal stream and wind must be confirmed. Attempts should not, whenever possible, be made to anchor across the current, tidal stream or wind. When all the way has been taken off the vessel, the vessel's head should be close to the direction of the tidal flow or wind, and the bow should not be swinging excessively.

Planning for Anchoring:

Master Should identify a suitable anchoring position before entering the anchorage area. Conduct a planned approach including speed reduction in ample time and orienting the ship's head before anchoring to
(a) Same as similar sized vessels around or (b) Stem the tide or wind whichever is stronger

A decision on the method of anchoring and the number of shackles to use depends upon the depth of water, expected weather, and holding ground. A simple rule in determining length of cable to use:

Standard condition:
Length of cable = [(Depth of water in meters * 2) + 90 ] / 27.5
When good holding power can not be expected e.g. strong wind, strong current, harder sea bottom etc. then the length of cable = [(Depth of water in meters * 3) + 140 ] / 27.5

It is suggested that the use of a radar parallel indexing technique is a useful tool in maneuvering approach to anchoring position. A fixed reference point is necessary for establishing the intended anchoring position relative to this fixed point.

Preparation for Anchoring

The Chief Officer (or another experienced officer in lieu) must supervise letting go or weighing the anchors and should only assign experienced crew members to anchor work. Prior to Anchoring, the Chief Officer should be aware of:
  1. Approximate anchoring position
  2. Method of approach
  3. Which anchor to use
  4. Depth of water
  5. Method of Anchoring
  6. Final amount of Cables

Procedure of the Introduction to Anchoring
  1. At the Forecastle: Check brakes are on and clear the voyage securing devices. (Anchor Lashings, Bow Compressed Bar etc.)
  2. Start Hydraulic(Source of) Power of Windlasses
  3. Check Anchor Shape / Light
  4. Check Communication with the Bridge
  5. Check Lighting on Forecastle including torch , at night time
  6. Ensure all personnel are wearing Safety Helmets, Safety Shoes and Goggles.

Before Letting Go Anchor :

The Chief Officer should confirm that there is no craft or any obstacle under the bow and inform to the Bridge. The Master should ensure that the vessel's GPS speed at the time of anchoring is near-zero or indicates a slight sternway. The speed should be verified by visual transits and Radar ranges of Landmarks if available or other fixed conspicuous targets. Whereby means of communication between Bridge and the Anchoring party is Portable radio, the identification of the ship should be clear to avoid misinterpretation of instructions from other users of such equipment in the vicinity.

Routine Anchoring Operation

There are 2 methods for Anchoring according to depth of the water:

Method 1 (Preferable for Container Ships / Depths up to 50m )
  1. Walk out the anchor to Half a shackle above the sea bottom
  2. Hold the cable on the brake and take the windlass out of gear
  3. Stop the vessel over ground
  4. Drop the anchor
  5. Control the speed of cable flow by the brake , while not allowing pile-up
  6. Bring anchor cable direction forward and confirmed anchor holds its position.
Disadvantages:

If the brake fails, or there is too much speed over the ground, the cable will run out to the bitter end with consequent damage. The brake lining could also be damaged due to this Dynamic load (the Static load on brakes to restrain movement of an anchored vessel is much less).

Method 2 (Suggested for Tankers / Depths over 50m )
  1. Stop the vessel over ground
  2. Walk out the anchor under power until the complete length of required cable is paid out, and the anchor holds its position on the seabed.
  3. Bring anchor cable direction forward and confirmed anchor holds its position.

Disadvantages: A vessel must be completely stopped to avoid significant damage to Windlass.

Particular Caution for VLCCs

VLCCs, because of their inertia, requires excellent caution while anchoring. They can suffer equipment failure if attempting to anchor while moving at speeds as low as half a knot over the ground. Hence, the vessel must be nearly stopped not only in the linear direction but axial, too, meaning the bow should not be swinging much either while anchoring. The depth at which the vessel can safely anchor is about 110m or less, beyond which the Windlass may have extreme difficulty in recovering the anchor. Refer further Practice of anchoring / VLCC in deep water for more details.

Emergency Anchoring

Anchors should be ready for letting go on arrival and departure port, when in anchoring depths. At least, any wire lashings are to be removed, and the anchors held on the brake. In critical situations, to arrest the movement of the vessel, after stopping/reversing the main engine, it is preferable to let go both anchors simultaneously instead of one.

Anchor retrieval

For weighing in the anchors, to reduce the load on the Windlass, and keep the cable near vertical, as required, short movements to be given on the main engine (and Bow Thruster used, where is applicable). The stay and direction of the cable and the residual shackles are continuously reported to the Bridge. Anchor Wash to be run to clean the chain and the anchor. When the anchor is fully hove, the brake is to be applied, and the Windlass is taken out of gear. The bow stopper is to be put when it is deemed safe to do so.
anchor chain ranged for inspection
Fig: anchor chain ranged for inspection


Note: If it does not engage properly on the chain, then it is to be lowered across the chain as far as possible and lashed down in this position in such a manner, that if the cable does slip, the bar will fall into place across the chain.

Anchor watch: An anchor watch is to be always kept when the ship is at anchor. Anchor Watch Checklist is to be used

Further reading: SKULD club guideline on good anchoring practice


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