RoRo Ferries – Construction

Q. What kind of vehicle details are provided for parking space on Ro-Ro ferries?
In order to provide information to the cargo planners, stevedores, etc. The information in respect of length, width, height and load (t/axis) etc. is provided.

Q. How is the width of lane related to the width of cargo space?
The width of the cargo space should be equal to or slightly more than the multiple of the lane width.

Q. Generally, what are the requirements regarding internal ramps?
The slope of the internal ramps is normally between 1:7 to 1:10. This means the slope angle will be about 7o. The width of ramp should be appropriate to serve the cargo on the relevant deck. The ramp surface must be non skid type. Usually, the large ships have the ramps up to 12m in width.

Q. What are general features of a PCC?
The PCCs have large windage areas. A considerable part of the hull and deck becomes exposed to weather. Depending on the deadweight, there are multiple decks. The decks are accessible by the use of internal ramps, liftable decks, etc. There are a large number of ventilators to comply with the SOLAS regulations. The bow area may have a visor or an arrangement whereby a ramp can be lowered on the deck. The arrangements are such that the watertightness is ensured till the bulkhead deck. Above bulkhead deck, the extension can be weathertight. There are stern ramps and side doors to facilitate a quick turnaround. The most striking feature of these ferries is that the entire ship is subdivided only in three or four vertical zones. The obvious feature then being large multiple decks in each zone. The stability usually becomes vulnerable after the water enters the hull and creates free surface on several decks. Several features/equipment viz. stern door, hoistable ramps, stern ramp, side ramps, ramp covers, bulkhead doors, car decks, shell doors are usually typical about such ships.

Q. What are the different types of ramps?
PCCs and Ro-Ros have several decks. Ramps provide access from one deck to the other. It is a large steel structure with longitudinal and transverse strengthening, used to drive in and drive out vehicles at varying tides.
For the large trucks, trailers, etc., the slope of the outer ramps and the internal ramps is maintained between 8 & 9 degrees. The ramps can be of different types as described below:

Foldable Stern Ramp with door
The ramp usually would have the span hinged to provide a long radius or reach. The hinge movement (to retract or to extend) is by hydraulics. The turning about the deck can be by winches and wire ropes. Alternately, the entire system could be worked on hydraulics or by wire ropes and winches. In the closed position, the inner section of ramps becomes weather tight. There is a provision of sequential interlocking when the ramp approaches its closed position.

Side Ramp
To be adaptable to the quays of varying heights is an important feature of these ramps. The slope can be adjusted easily. The flaps completely rest on the quay even at a few degrees list. The ramp is operated by wire ropes or hydraulic rams. In closed position, the door acts as a weather tight door. The stainless steel bar around the ramp presses against the rubber gasket to provide weather tightness. These can be on port side or starboard side or both the sides.

Bow ramps
There is generally the bow opening having a visor or side-hinged bow door. Once the bow door or the visor is opened up, the ramp which otherwise provides water tightness till the bulkhead deck can be opened.

Internal ramps 
Fixed or hinged internal ramps are used for the mobility of cars, trailers, etc. Mechanically / hydraulically-operated steel covers are installed in association with fixed internal ramps. The ramp covers must comply with the requirements in respect of load carrying capacity and watertightness, slope, etc. They can be either side-hinged or end-hinged as required.

Tiltable ramp 
These flexible ramps can be provided with flaps and hydraulically disconnectable hinges at both ends. The hinge at either forward or after end, can be secured to the upper of the two decks, allowing the opposite end to be lowered to the other deck.

Quarter Ramp
These ramps can be used on normal jetties with part of the load taken by the system. These ramps have better flexibility in respect of tidal variation. The ramp acts as a weather tight door when closed. This type of ramp is capable of taking heavy loads. When in sea going position, the ramp closes weather tight. The first and the second section fold using hydraulically operated cylinders. It takes about 25 min to lower a ramp of big size. The ramp can be placed at an angle of 30o and 45o to the centre-line.

Q. What are the features of a ramp, which an architect must carefully work on and provide details about? 
The various features in respect of a ramp are:

  • length and width;
  • expected maximum load;
  • maximum axle load;
  • hoisting arrangement details;
  • limiting operating angles or range;
  • watertight / weathertight arrangements;
  • cleats / locks / manual securing arrangements;
  • time required to lower / hoist; and
  • details of limitations. Thus, tide or wharf related issues.

Q. What are the different types of movable decks?
A flexibility is provided in the stowage of car inside the ship, particularly if the load that would be taken is of light vehicles. There may be hoistable car decks whereby electrical or hydraulic machinery is employed in their mobility. The decks may be lifted vertically and the mechanism may be telescopic, scissor based or chain operated.

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