2.1 Roll-on/Roll-off (RoRo) Merchant Vessels
RoRo vessels, also known as roll-on/roll-off ships, are a vital part of the modern maritime transportation system.
Unlike traditional cargo ships that rely on containers, RoRos are designed for the efficient loading and unloading of wheeled cargo.
This chapter details different types of RoRo vessels, their characteristics, functionalities, and the specific equipment onboard.
The world of RoRo is diverse, with different vessel types catering to specific cargo needs including :
Pure Car Carrier (PCC): These giants of the sea specialize in transporting finished cars. They have multiple decks with minimal fixed structures, maximizing car-carrying capacity.
Pure Car and Truck Carrier (PCTC): As the name suggests, these RoRos handle both cars and trucks. They offer a mix of open decks for cars and enclosed decks for trucks.
Trailer/Container Carrier: These versatile vessels can accommodate both trailers and standard shipping containers. They often have cranes onboard for container handling.
Ferry: These smaller RoRos operate on shorter routes, transporting passengers, vehicles, and sometimes cargo across rivers, bays, or channels.
RoPax : A ropax ferry is a vessel that combines the features of a cruise ship and night cabins with a roll-on/roll-off ferry. They are also known as RoPax for their combined Roll on/Roll Off and passenger design.
General Characteristics of RoRo Vessels
Several key characteristics define RoRo vessels include:
Ramps: The defining feature of a RoRo is the presence of built-in or shore-based ramps. These ramps allow vehicles to drive on and off the ship efficiently.
Multiple Decks: To maximize cargo capacity, RoRos have multiple decks connected by internal ramps. These decks can be fixed or hoistable to adjust for varying cargo heights.
Securing Equipment: Since cargo is not containerized, RoRo vessels employ special lashing points and equipment to secure vehicles during transport.
Specificities of RoRo Operations
RoRo operations differ from traditional cargo handling in several ways:
Faster Loading/Unloading: The roll-on/roll-off method allows for significantly faster loading and unloading times compared to container ships that require cranes.
Weather Dependence: Due to the reliance on ramps, RoRo operations can be susceptible to bad weather conditions that might affect safe ramp deployment.
Safety Measures: Stringent fire safety regulations exist for RoRo vessels due to the presence of vehicles with flammable materials onboard.
Watertight Doors: Protection Against Flooding on RoRo Vessels
While RoRo vessels excel at getting cargo on and off quickly, the large open space decks for vehicle access presents a unique challenge: maintaining watertight integrity and stability. This is the crucial role of watertight doors.
Unlike traditional cargo ships, RoRos lack a solid bow and stern due to the need for vehicle access ramps. To maintain watertight integrity in these areas, RoRo vessels utilize special watertight bow and stern doors. These massive doors create a watertight seal when closed, essentially transforming the open ramp area into a secure compartment.
These doors are built to withstand immense pressure, ensuring they can hold back seawater even in the event of significant flooding.
Equipment Onboard a RoRo Vessel
Onboard, large vehicle decks can also be subdivided with watertight bulkheads and doors icluding :
• Hinged Doors: Common for smaller openings, these swing open and closed but require more deck space.
• Sliding Doors: Often used for larger openings, these slide horizontally along tracks, saving space on deck. On RoRos, these are typically remotely operated for added safety and efficiency.
By compartmentalizing the ship and preventing water ingress, they play a critical role in maintaining buoyancy, stability, and crew safety during critical situations.
As part of a comprehensive damage control system, regular maintenance and crew training on operating these doors are essential for ensuring their effectiveness.
Drills simulate closing procedures and verify watertight integrity, safeguarding the vessel and crew in case of emergencies.
• Mooring Winches: These powerful winches ensure the safe and precise mooring of the vessel during loading and unloading.
• Ballast Water Systems: RoRos employ ballast water systems to maintain stability as cargo is loaded and unloaded, which can affect the vessel's center of gravity.
• Cargo Lifts: While the main focus is on wheeled cargo, some RoRos might have cargo lifts to handle non-wheeled items on specific decks.