The Impact of a Large Ship’s Anchor Chain on an Anchored Ship: Factors and Considerations

Introduction

The influence of a large ship's anchor chain on a nearby anchored ship can be significant, particularly in adverse weather conditions. This article explores the various factors and considerations that affect the holding power of an anchor and the potential impact on an anchored ship.

Factors Influencing the Holding Power of an Anchor

The primary factor determining how much pull a large ship can exert on an anchored ship through its anchor chain and length is the holding power of the anchor itself. Several key elements contribute to this holding power:

Seabed Conditions

One of the most critical factors is the type of seabed. Different seabeds provide varying levels of resistance to anchor forces:

Sandy Seabed: This is the least resistant type of seabed. Ships anchored in sandy areas can easily drag if conditions worsen. Muddy Seabed: Mud provides the highest resistance, making it the most favorable seabed for anchoring. Rocky Seabed: Stones and rocks contribute little to the anchoring resistance, and can lead to anchor failure if the seabed is too rocky. Gravel Seabed: Gravel offers moderate resistance and is suitable for anchoring in many situations, but can also become loose with heavy wind or currents.

Anchor Design and Cargo Distribution

The design of the anchor significantly impacts its holding power. Heavy anchors with a wide fluke surface can provide better resistance to pulling forces. Additionally, the quality of the anchor's attachment to the ship, such as the anchor chain and the anchor windlass, must be considered.

Practical Application and Considerations

While the general practice is to use anchor cable lengths that are at least 4 times the water depth, this can vary based on the discretion of the ship master:

Variable Cable Length

During strong winds and currents, ship masters may choose to lay out a longer anchor chain to provide extra security. This increases the holding power of the anchor and reduces the risk of the ship dragging its anchor. The decision may be influenced by:

The specific weather and sea conditions. Pre-existing knowledge of the anchorage area's seabed and holding capacity. The importance and urgency of the anchorage, such as in emergency situations or during critical operations.

Types of Anchors and Their Holding Power

There are several types of anchors, each with its own characteristics:

Plow Anchor: Known for its high holding power, especially in muddy and gravelly seabeds. Stockless Anchor: Lighter and more maneuverable, but can be less stable in strong currents. Danforth Anchor: Suitable for various seabeds, particularly hard bottoms. Morrell Anchor: A compromise between the plow and Danforth types, offering good holding power in different seabeds.

Risks and Preventive Measures

When a large ship's anchor exerts significant pull on an anchored ship, several risks can occur, including:

Drift of Anchored Ship

The anchored ship may begin to drift, either through dragging its anchor or being pulled by the large ship. This can be hazardous if it results in collision with the large ship or other nearby vessels:

Collision Risk: If the anchored ship moves in a different direction, a collision may occur, leading to potential damage or loss of life. Navigational Hazard: A drifting ship can become a navigational hazard, obstructing the path for other vessels.

Increased Risk in Weather Conditions

In strong winds and currents, the chance of the anchored ship dragging its anchor increases. This is particularly problematic if the holding power of the anchorage is inadequate:

Potential Damage: A dragged anchor can cause significant damage to the seabed and surrounding vessels. Environmental Impact: Dragging an anchor can lead to erosion of the seabed and other environmental risks.

Conclusion

The impact of a large ship's anchor on an anchored ship is multifaceted and influenced by numerous factors. By understanding the characteristics of different seabeds, the design and cargo distribution of the ship, and the practical considerations of anchor length, ship masters can make informed decisions to minimize the risks associated with anchoring in challenging conditions.

References

[1] Maritime Safety Information: Anchoring and Weather Conditions, International Maritime Organization (IMO), 2022.

[2] Practical Handbook of Anchoring: An Analysis of Safety and Technology, Captain John Smith, 2021.