Sea cargo reference
Ro/Ro
Cargo rolls on and rolls off. The notes below cover the cargo, the way the hull is arranged, and the limit that puts a ship in this class.
- Ship's gear
- Stern, quarter or side ramps
- How capacity is counted
- Lane metres; car equivalent units (CEU)
- Usual size
- Car carriers commonly 4,000-8,000 CEU; the newest exceed 10,000 CEU
- Cargo type
- Wheeled and tracked cargo
Ro/ro ships
Roll-on/roll-off means the cargo is driven aboard over a ramp, not lifted. The name covers pure car carriers, ro-pax ferries and ro-ro freight ships.
Capacity is counted in lane metres, or in car equivalent units on a vehicle carrier. Ramps join the internal decks. Several decks can usually change height, so the same ship can carry cars on one voyage and tall machinery on the next.
Loading is very fast, which is what makes short-sea ferries and vehicle export trades work. The matching design problem is the large open vehicle deck, which has to be managed carefully for stability and for fire.
Cargo on board
How the hull is arranged
- Deck heights can be changed, so the crew can reset the ship between cars on one voyage and tall machinery on the next.
- Hull and gear are drawn around one cargo, not around general trade.
- The handling fit matches the trade: heavy-lift derricks, stern or side ramps, ventilation, or a refrigeration plant.
- The structure is strengthened where that cargo needs it, for point loads, vehicle decks, or several tween decks.
Why this trade uses it
- Takes cargo a general ship cannot carry safely or at a workable cost.
- Built-in gear keeps port time short where the shore has little equipment.
- For many of these trades it is the only practical ship.
Settle these points before you fix
- The trade is narrow, so ships are scarce and the rate is less competitive than open-market tonnage.
- The return voyage is often in ballast, because the special fit has nothing to load home.
- Many of these trades add their own rules on top of ordinary cargo law.