Athwartships – Perpendicular to the ship’s longitudinal axis

Athwartships is a maritime term used to describe orientation or direction across the ship, from one side to the other, at a right angle to the keel or the longitudinal axis of the ship. This term is crucial in a maritime context, especially when stowing and securing cargo, such as shipping containers, where understanding the stresses and load-bearing capacities is essential for safe and efficient operations.

Definition and Etymology

The term “athwartships” originates from the combination of “athwart,” meaning across or in opposition, and “ships,” referring to the maritime context. Its first recorded use dates back to the early 18th century, highlighting its long-standing importance in maritime terminology. The word refers to a direction that is perpendicular to the longitudinal axis of the ship, thus covering the width of the vessel.

Significance in Maritime Operations

The athwartships orientation is important in various maritime operations, especially in the context of container transport and cargo stowing. When containers or cargo are stowed athwartships, they are placed across the vessel, affecting the vessel’s balance and weight distribution. This is critical because the design of containers and ships is often stronger along the longitudinal direction (fore and aft) than across (athwartships).

Stowing and Securing Containers

In container transport, containers can be stowed longitudinally (fore and aft) or transversely (athwartships). Each method has implications for the stability of the ship and the stresses acting on the containers and the vessel itself:

1. Longitudinal Stowing: This method aligns containers with the length of the ship and is generally preferred due to the greater strength of the side walls of containers compared to the front walls. It offers better resistance to dynamic forces in rough seas. According to the Container Handbook, this method is sensible due to the interaction of stresses in rough seas and the load-bearing capacity of the containers.
2. Transverse Stowing: Although less common, this method is sometimes used due to spatial constraints or specific loading requirements. However, it poses challenges due to the higher stresses caused by waves and wind across the width of the vessel, requiring careful securing to prevent slippage or tipping. Industry sources, such as the Wärtsilä Encyclopedia, note that this method is less sensible in terms of stress distribution, but is sometimes necessary.

Design Considerations

When containers are stowed athwartships, several design considerations come into play:

• Stress in Rough Seas: Containers stowed athwartships face higher lateral forces during rough seas, which can lead to an increased risk of structural damage if not properly secured. The Container Handbook emphasizes that the stresses are greater athwartships than longitudinally, requiring more robust securing techniques.
• Load-Bearing Capacity: The load-bearing capacity of the front walls of a container is usually lower than that of the side walls, making longitudinal stowing generally more sensible. However, when transverse stowing is necessary, additional precautions should be taken to ensure safety. The maximum load on the CSC plate or in documentation should always be considered to avoid overloading.
• Securing Mechanisms: To counteract the increased stress, containers stowed athwartships are often secured using vertical guides, securing rods, and twist locks. These mechanisms help stabilize the containers and evenly distribute forces across the vessel’s structure. As seen in practical handbooks, the use of securing rods and stacking cones is crucial for maintaining stability.

Challenges and Solutions

The use of athwartships stowage presents unique challenges, particularly regarding balance and structural integrity. These challenges require specialized solutions and careful planning:

• Balance and Stability: Proper balance is crucial to avoid tilting or capsizing the vessel. Advanced software and careful planning are used to ensure optimal weight distribution and balance across the vessel.
• Securing Techniques: Containers stowed athwartships require robust securing techniques such as stacking cones, securing rods, and twist locks to prevent movement during transport. These techniques are essential to minimize the risk of cargo shift, which can have catastrophic consequences.
• Weather Conditions: The stowage method may also depend on the expected weather conditions. In scenarios where rough seas are anticipated, longitudinal stowage is often preferred to reduce the impact of lateral forces.

Practical Applications

Understanding the concept of athwartships and its implications is crucial for various maritime professionals, including shipbuilders, cargo planners, and marine engineers. It informs decisions regarding ship design, cargo loading, and container securing, ensuring safety and efficiency in maritime operations.

Cargo Containers

In the context of cargo containers, athwartships stowage is a critical consideration in container ship design. The ability to safely stow containers both longitudinally and athwartships provides flexibility in cargo operations and maximizes the use of available space. As highlighted in container stacking guides, proper alignment and securing are key to preventing accidents.

Naval Architecture

For naval architects and engineers, the orientation of athwartships influences the design and reinforcement of vessels. It requires careful calculations of stress distribution and the implementation of elements such as vertical guides and reinforced corner posts to counterbalance the unique forces at play.

The term “athwartships” is a fundamental concept in the maritime industry, integral to the safe and efficient stowage of cargo and the structural integrity of vessels. While it presents challenges, particularly with regard to balance and stress management, advances in technology and engineering continue to improve the ability of maritime professionals to effectively handle these challenges. Understanding the athwartships orientation not only contributes to safer maritime operations but also optimizes space and resource utilization in the global shipping industry.