RO-RO
VESSELS
Roll-on/roll-off ships, designed for the carriage of wheeled
cargo, feature a high freeboard, three- or four-deck superstructure,
and twin funnels placed athwartships. They are fitted with doors
in the hull (most often at the ends), internal ramps and elevators
for deck-to-deck transfers, and external ramps to join the hull
doors to the pier. Often the main or only door is in the stern,
facing directly aft and fitted with a massive folding ramp exterior
to the hull. The ramp is capable of slewing - i.e., rotating
so that it can be landed on a pier alongside the ship.
To ensure stability, fixed ballast is usually included in these
ships, along with water ballast to adjust load and stability.
The engineering plants are commonly twin diesel engines and
they are arranged so that the engine spaces are at either side
of the ship, allowing valuable free space between them for vehicle
passage. Propulsion is by two CPP (controllable pitch propellers)
and a bow thruster fitted forward.
Ro-Ro vessels can be classified into a Ro-Ro passenger/car ferry
and a Ro-Ro unit load ship according to what they carry. Obviously,
the latter carries trailers or TEU's (Twenty-foot Equivalent
Unit). If conventionally packed, cargo is delivered at the quayside
and then packed in containers before shipment. Cargo handling
gear is optional, usually, if fitted, it consists of derricks
or deck cranes. Ferries carrying passengers are equipped with
dining saloons and other public rooms and are more like versions
of passenger liners.
