Marine structures play a crucial role in facilitating maritime activities, protecting coastlines, and supporting the operations of ships and vessels. These structures are designed to withstand harsh environmental conditions such as ship impacts, sea wave forces, and changing weather patterns. Marine structures are primarily categorized based on their function, and the materials used for their construction vary depending on the specific needs of the structure. In this article, we will discuss the different types of marine structures, the materials used for their construction, their design considerations, and their key functions.
Introduction
Marine structures are integral to the functioning of maritime industries, ports, and coastal management. They serve a variety of purposes ranging from supporting ships to protecting the coastline from the erosion caused by sea waves. Common materials used in the construction of marine structures include concrete, stone, timber, and steel. These materials must be durable enough to withstand the extreme conditions of the marine environment. Furthermore, the design of these structures must account for various types of loads, including service loads, ship impacts, and the forces generated by sea waves. While the average lifespan of most marine structures is about 25 years, some have remained in service for 75 years or even over 100 years.
Types of Marine Structures
Marine structures can be broadly categorized based on their function. The primary categories include berthing facilities, dry docking facilities, and coastal protection structures. Each category serves a distinct purpose and is designed to fulfill specific maritime or coastal needs.
1. Berthing Facilities
Berthing facilities are crucial for providing safe and stable docking areas for ships. These structures are designed to support ships during loading, unloading, and boarding of passengers, and to facilitate smooth transitions between ships and land transport. Berthing facilities can be constructed either parallel or normal to the shore, depending on the particular application. Key types of berthing facilities include piers and wharves.
Piers
Piers are structures that extend from the land into the sea, providing a platform for ships to dock. Piers are typically built perpendicular to the shore, reaching into deep waters, and they are often used for both passenger and cargo handling. The length of a pier is typically determined by the size of the largest ship it will serve, with piers either matching or exceeding the ship’s length. There are three main types of piers:
- Open piers: These are either single or double-deck structures supported by piles, allowing water to flow underneath.
- Closed piers: These piers consist of a solid fill structure, such as a quay wall or anchored sheet pile, which prevents the flow of water beneath the structure.
- Floating piers: These piers are anchored to the shore by a ramp and are designed to rise and fall with changes in water level, providing stability even in fluctuating conditions.
Wharves
Wharves are similar to piers but are constructed parallel to the shore and are typically not connected directly to the land. They are primarily used for loading and unloading cargo or for ship docking. Unlike piers, which support ships on both sides, wharves can support ships on only one side. Wharves can be designed as solid fill or open platforms, depending on the needs of the harbor. Some wharves are supported by piles and are built away from the shore if the water near the coast is too shallow for large vessels. Trestles, which are elevated platforms supported by piles, may be used to connect the wharf to the shore.
2. Dry Docking Facilities
Dry docking facilities are essential for the construction, maintenance, and repair of ships. These structures allow vessels to be removed from the water for inspection, cleaning, repairs, and modifications. Several types of dry docking platforms exist, including floating dry docks, graving dry docks, vertical synchro lifts, and marine railways.
Floating Dry Dock
A floating dry dock is a large, U-shaped structure that can lift ships out of the water. The dry dock is first submerged by filling it with water, allowing a ship to be positioned inside. After the ship is in place, the water is drained, and the dock rises, lifting the ship out of the water for maintenance.
Graving Dry Dock
Graving dry docks are large, stationary structures typically built adjacent to the land. These docks are often made from concrete, masonry, sheet piles, or stones. When a ship enters a graving dry dock, the entrance is sealed with a water-impervious barrier, and water is pumped out, allowing the ship to rest on blocks within the dock for inspection and repairs.
Vertical Synchro Lifts
Vertical synchro lifts are a type of dry docking platform where the entire structure is lowered into the water. Ships are then loaded onto the platform, which is subsequently raised to a predetermined height for maintenance.
Marine Railways
Marine railways consist of ramps that extend into the water, along with a mobile cradle that can carry ships or containers in and out of the water. These systems use cables and hosting equipment to facilitate the movement of ships onto and off the platform.
3. Coastal Protection Structures
Coastal protection structures are built to safeguard coastlines from the damaging effects of sea waves, particularly erosion. These structures are designed to create a barrier between the sea and the land, preventing damage to properties, harbors, and other coastal infrastructure. Types of coastal protection structures include bulkheads, seawalls, groins, jetties, and breakwaters.
Bulkheads
Bulkheads are vertical walls constructed along the shoreline to prevent erosion and protect the land from wave action. These structures provide a physical barrier to the sea, reducing the impact of high waves on the coastline.
Seawalls
Seawalls are solid barriers built parallel to the shoreline to protect the land from the damaging effects of sea waves. Seawalls are typically constructed from concrete or stone and are designed to absorb and dissipate the energy of incoming waves.
Groins
Groins are long, narrow structures built into the sea at right angles to the shoreline. They are designed to trap sand and prevent beach erosion. Groins help maintain the stability of beaches by limiting the movement of sand caused by longshore drift.
Jetties
Jetties are structures built to protect harbors and inlets from the force of waves and to prevent sediment accumulation at the entrance. Jetties are often constructed at the mouth of a harbor to control water flow and improve navigation.
Breakwaters
Breakwaters are structures built offshore to reduce the energy of incoming waves and protect harbors, ports, and coastal areas. These structures are designed to dissipate wave energy before it reaches the shore, preventing erosion and damage to coastal infrastructure.
Conclusion
Marine structures are essential for supporting maritime activities, protecting coastlines, and ensuring safe navigation for vessels. Berthing facilities, dry docking platforms, and coastal protection structures each serve specific functions that are vital for the smooth operation of ports and harbors. The materials used in their construction must be durable enough to withstand harsh marine environments, and their designs must take into account the forces of waves, ships, and other environmental factors. The longevity and functionality of marine structures are essential for maintaining the efficiency of maritime industries and protecting coastal regions from the damaging effects of sea waves.