10.4 Anchoring
Explain:
- The procedures for anchoring with one or two anchors
- Factors for deciding the scope of the cable
- Swinging circle
- Procedures and precautions taken for anchoring in deep waters and shallow waters
- Running moor
- Standing moor
- Open moor
- Mediterranean moor
Dragging anchor
Describe:
- Actions taken when vessel starts dragging its anchor(s)
- How to slip anchor(s)
When it comes to anchoring, a combination of seamanship practices, maritime regulations, classification society guidelines, P&I (Protection and Indemnity) club recommendations, and understanding of naval architecture and flow dynamics theories are important. Here's an explanation based on these references:
Procedures for Anchoring with One or Two Anchors:
Anchoring with One Anchor: The procedure for anchoring with one anchor involves selecting a suitable anchorage, maneuvering the vessel into position, and dropping the anchor to the seabed while paying out the anchor chain. The anchor is then set by applying tension to the chain using the vessel's propulsion or windlass system. Adequate scope should be provided to ensure proper holding power.
Anchoring with Two Anchors (Double Anchoring): Double anchoring is commonly used in areas with strong winds or currents. The procedure involves dropping both anchors at a suitable distance apart from the vessel, forming a V-shaped configuration with the vessel at the apex. The anchors should be set alternately, and the vessel's position should be monitored to ensure both anchors are adequately holding.
Factors for Deciding the Scope of the Cable:
The scope of the anchor cable (chain) refers to the ratio of the length of the cable to the vertical distance between the anchor and the seabed. Factors to consider when deciding the scope include:
Water Depth: The depth of the water determines the minimum length of chain required to ensure proper anchoring.
Wind and Current Conditions: The strength of wind and currents should be considered when determining the scope. Higher wind or current speeds may require a greater scope to provide sufficient holding power.
Seabed Conditions: The nature of the seabed, such as its holding capacity and the presence of rocks or obstacles, influences the scope. A larger scope may be necessary for less favorable seabed conditions.
Swinging Circle:
The swinging circle refers to the area that a vessel occupies as it swings around its anchor point. It is influenced by factors such as wind, current, and vessel size. When anchoring, the swinging circle should be clear of obstructions, other vessels, or navigational hazards to ensure safe maneuvering.
Procedures and Precautions for Anchoring in Deep Waters and Shallow Waters:
Anchoring in Deep Waters: In deep waters, additional precautions may be necessary due to the increased potential for anchor drag or inadequate holding power. A longer length of anchor chain may be required to provide an appropriate scope, and the use of multiple anchors may be considered for added security.
Anchoring in Shallow Waters: In shallow waters, care must be taken to avoid grounding or damage to the vessel's hull or keel. The anchor chain should be paid out gradually to prevent sudden shock loads, and regular depth soundings should be taken to monitor the vessel's clearance from the seabed.
Running Moor, Standing Moor, Open Moor, Mediterranean Moor:
These terms describe different anchoring techniques:
Running Moor: In a running moor, the anchor is dropped while the vessel is moving slowly forward. The vessel continues to move ahead while paying out the chain until the desired scope is achieved. This technique is often used when anchoring in narrow channels or when precise positioning is required.
Standing Moor: In a standing moor, the vessel is brought to a stop, and the anchor is dropped. The anchor chain is paid out until the desired scope is reached, and the vessel holds its position.
Open Moor: In an open moor, the vessel is anchored using a single anchor, allowing it to swing freely with wind and current changes. This technique is commonly used in open waters with sufficient space and without nearby hazards.
Mediterranean Moor: The Mediterranean moor involves dropping both anchors astern while at a berth or anchorage. This technique provides additional stability and prevents the vessel from swinging or drifting.
Dragging Anchor:
When a vessel starts dragging its anchor(s), prompt action is necessary to prevent drifting into hazards or other vessels. The actions to be taken include:
Alerting the Bridge Team: The crew should immediately notify the bridge team and raise the alarm to ensure everyone is aware of the situation.
Engaging Additional Anchors: If available, additional anchors can be dropped to provide extra holding power. This may involve using a different anchoring technique, such as a tandem anchoring configuration.
Increasing Scope: Paying out more anchor chain to increase the scope can enhance holding power and reduce the risk of further dragging.
Engaging Auxiliary Propulsion: If the vessel has auxiliary propulsion, such as a bow thruster or stern thruster, it can be used to counteract the dragging motion and assist in regaining control.
Slipping Anchor(s): Slipping the anchor cable or cables is a last resort action taken in emergency situations when a ship is unable to heave or raise the anchor(s). It involves intentionally releasing the anchor(s) from the seabed to quickly free the vessel and allow it to proceed to a safer location or navigate out of a hazardous situation.
During the process of slipping the anchor, the anchor chain or cable is released rapidly, often by cutting or disconnecting it, to detach the vessel from the anchor. This action is taken when there is an immediate threat to the safety of the vessel, such as in cases of severe weather, impending collision, or other emergencies that require the ship to get underway quickly.
It is important to note that slipping the anchor should only be done as a last resort when all other means of recovering the anchor or properly weighing it are not possible due to time constraints or extreme circumstances. The decision to slip the anchor should be made with careful consideration of the potential consequences and the vessel's overall safety.
After slipping the anchor, the vessel should proceed to a safe area or navigate to a location where further assessments and necessary actions can be taken to address the emergency situation appropriately. The incident of slipping the anchor should be reported in the vessel's logbook, along with the details of the circumstances leading to the decision and any actions taken afterward.