The anchoring procedure is typically divided into three key phases: Planning, Execution, and Monitoring. Each phase is crucial for ensuring the safety and effectiveness of the anchoring process, as even minor miscalculations or oversight can lead to serious consequences.
Phase #1: Planning
The first stage of the anchoring procedure involves identifying the need for anchoring. This means that the ship’s operational schedule includes a specific requirement for the ship to anchor. Anchoring may be necessary for various reasons, such as bunkering, loading supplies, or adhering to a timetable—like waiting for permission to enter a port or for a lay-up. In some instances, anchoring is required for more complex operations, such as ship-to-ship (STS) transfers.
Regardless of the reason for anchoring, the planning process follows a similar approach. The Master (or the officer responsible for planning the anchoring) must carefully consider a range of parameters, including the characteristics of the area, prevailing weather and environmental conditions, and the specific attributes of the ship.
Critical factors in ensuring a safe and efficient anchoring operation
A. Area-related parameters
A1. Free space for anchoring
When approaching a port’s anchoring or waiting area, there are often numbered specific positions, with local authorities assigning ships to these designated locations. However, this is not always the case. In many ports, the Master must choose the anchoring position before arrival, without knowing the status of nearby vessels.
Therefore, it is essential to plan for an alternative anchoring point to avoid space constraints in case the initial chosen spot is already occupied by other ships. To ensure adequate sea room, the anchor’s safety circle (as discussed in the “Anchoring Watch” article) should be drawn in advance, using both ECDIS and paper charts.
A2. Bottom holding quality
Dropping the anchor on a chosen point does not necessarily guarantee that the anchor will hold the ship in place. For the anchor to effectively secure the ship, its flukes must penetrate the seabed and provide sufficient grip to allow the chain to hold the vessel steady. The navigator planning the anchoring should gather information about the seabed’s quality and the holding capacity of the anchor for the area.
A3. Absence of navigational hazards
It is crucial to ensure that the anchoring area is free from navigational hazards, such as pipelines, sea bottom cables, wrecks, and other obstructions. A thorough survey of the area is necessary to confirm that no hazards will interfere with the anchoring operation.
A4. Distance from port facilities
If the anchoring position is not assigned by the port authorities, the officer planning the anchorage should aim to position the ship as close as possible to the port facilities, provided it is permitted by local regulations and environmental conditions. This helps minimize the time and resources required for the ship to access port services when needed.
A5. Anchoring depth
The depth of water at the anchoring site is a critical factor in determining the length of the anchor chain required to secure the ship.
Different rules exist for calculating the necessary chain length, and certain ports may impose specific restrictions on chain length, especially in congested anchorages (e.g., Singapore, where there are guidelines based on ship types). The most common methods for calculating chain length are:
a. Amount of cable required (in shackles) = 1 ½ √water depth in meters (Admiralty Manual of Seamanship)
b. Minimum amount of cable required (in meters) = 4 x depth of water in meters (D.J. House – Seamanship Techniques)
In addition to these calculations, prevailing weather conditions should be considered to determine if additional chain is needed to ensure secure anchoring.
B. Weather/Environmental related parameters
Like all aspects of maritime operations, anchoring is highly influenced by weather conditions and environmental factors.
B1. Wind/Wave
Prevailing wind conditions should be carefully monitored throughout all phases of the anchoring process.
During the planning phase, the approach course is closely related to the wind and wave status. Since the ship is likely not to be the only vessel in the area, the officer planning the anchoring must consider alternative approach options to ensure safe and efficient positioning.
Wave and swell conditions are also important, as they can affect the stability and safety of the anchorage once the execution phase is completed.
B2. Current
During the final stages of the anchoring procedure, when the ship is moving at very low speeds, it becomes highly susceptible to the prevailing currents. The ideal scenario is for the current, wind, and wave to come from the bow, as this allows the ship to be more easily handled with small adjustments in course and speed.
If this alignment is not possible, detailed planning is essential to account for the combined forces of wind, current, and wave during the final approach, ensuring that all relevant factors are carefully considered.
C. Ship-related parameters
The type of anchor, as well as the size and maneuverability of the ship, should be carefully considered during the planning phase.
C1. Turning ability
If the anchoring plan involves a turn at the final stage to counteract the forces of wind, wave, or current, the turning capabilities of the ship must be assessed. Understanding how the ship handles these forces is crucial for ensuring safe and precise anchoring.
C2. Size/Type of anchor and available chain length
Each ship is equipped with a specific anchor or set of anchors, chosen based on the ship’s construction and operational requirements. The anchors vary in number and weight, and the ship also carries a predetermined length of chain, measured in shackles (1 shackle = 15 fathoms or 27.5 meters). The amount of chain required for safe anchoring depends on the depth of the water at the chosen anchoring site and must be calculated accordingly.
C3. Forecastle preparation
The crew on the forecastle should be fully briefed on the anchoring plan and prepared to handle the chosen anchor for deployment. This ensures that the team is ready to execute the plan effectively and safely when the time comes to drop the anchor.
Phase #2: Execution
The execution of the anchoring operation is a precise navigational procedure aimed at guiding the ship to a predetermined position along a specific path, at a specific speed, so that the anchor is dropped as close as possible to the designated point.
A detailed navigational approach, with continuous control and positioning checks (via ECDIS or paper chart plotting), is essential. The points for reducing speed, backing astern, and dropping the anchor should be clearly marked and monitored during the approach.
This is the primary responsibility of the bridge team—to keep the ship on the designated track and execute the pre-scheduled actions (such as speed reductions) at the appropriate times.
The other team involved in the anchoring procedure is the forecastle team. This team typically consists of an officer in charge (often the Chief Officer), a windlass operator, and one or two supporting team members.
Once the ship is in position to drop the anchor, there are two primary methods for carrying out the task:
#1 The ‘’Letting Go’’ method
In this method, the operator releases the brake on the windlass to allow the anchor to drop, using gravity to let out the desired amount of chain. However, this method carries several risks. If not properly executed, the windlass brake may fail to stop the chain from being released, potentially causing damage to the anchoring equipment.
A common practice is to control the chain’s release until it reaches a level 7 to 10 meters above the calculated seabed depth, and only then to release the brake as the ship begins to back up. This gradual approach helps prevent excessive force on the brake. This method is typically used in shallow depths where the forces acting on the windlass system are minimal. The advantage of this method is that, in case of increased backing speed (due to engine power or increased wind/current from the bow), the additional power is absorbed by the chain, preventing further strain on the anchoring system.
#2 The ‘’Walking Back’’ method
The walking back method is similar to letting go, but with one key difference: the brake on the windlass is actively controlling the chain during the backing up process. This method allows for controlled lowering of the chain after it touches the seabed, as the weight of the chain remains constant (equal to the depth), preventing the chain from running out on its own. However, this method presents a significant risk if the backing speed exceeds the windlass’s design speed. If the backing speed is too high, the windlass brake must overcome both the weight of the chain and the force exerted by the anchor and chain dragging on the seabed. Therefore, careful calculation of the backing speed, taking into account wind and current conditions, is necessary before using this method.
Once the calculated chain length has been released, the chain should be secured to the chain stopper, and all relevant securing equipment should be applied. A good practice is to always install a connecting shackle before the stopper, allowing the remaining chain to be disconnected if necessary during emergency procedures.
Fixing the anchor position
Accurately plotting and fixing the anchor position on the chart (whether paper or ENC) is critical. This marks the starting point for measuring the safety circle and initiates the monitoring phase. Upon letting go of the anchor, the bridge team should use all available means (GNSS, visual observations, radar) to plot the exact position of the anchor.
Phase #3: Monitoring
Once the ship is securely anchored, a continuous watch must be established to monitor its position and prevent anchor dragging, which could potentially damage nearby ships or cause the ship to run aground.
Weighing anchor: The reverse of the anchoring process
When weighing anchor, the ship must lift the anchor and proceed to its next destination. Similar to the anchoring process, a detailed plan must be prepared, akin to a passage plan, with the anchoring position as the starting point. The surrounding area and available space for departure must also be carefully considered. In some cases, tug assistance may be required.
Key considerations when weighing anchor:
1. Wind and current at the time of departure
2. Traffic density in the area
3. Available navigational space
A continuous communication line should be maintained between the bridge team and the forecastle team throughout the operation. The heaving of the anchor should be carried out in a controlled manner. In some cases, the main engine may be engaged to assist with the heaving process and reduce the strain on the windlass.
The most critical stage is when the anchor flukes are ready to detach from the seabed, as the power applied to the windlass at this point is a combination of the chain weight extending to the seabed, the anchor weight, and the tension required to detach the anchor.
During the entire heaving process, the anchor washing system should be activated to wash away mud from the chain and anchor. The anchor is considered fully housed when the shank is inside the hawsepipe and the flukes are positioned against the ship’s side, clear of any obstacles. The forecastle team must secure the anchor for sea, using all available securing devices and stoppers.
In conclusion, anchoring is a highly skilled navigational operation that requires careful preparation, clear communication between teams, and a crew that is both competent and familiar with the equipment and procedures.
