Ro-Ro (roll-on/roll-off) ships carry vehicles and wheeled cargo that drive on and off over a ramp. In Indonesia, the best-known type is the passenger ferry (Ro-Pax) carrying trucks, buses, cars and passengers, alongside cargo Ro-Ro ships and pure car and truck carriers (PCTC) distributing new vehicles. This guide covers the basics of load planning for all of them.

Capacity: lane metres, CEU and free height

Ro-Ro deck capacity is measured in lane metres (LM), the total length of vehicle lanes. Car carriers often quote capacity in CEU (car equivalent units) based on a reference car. The third factor is the free height of each deck: trucks and buses need a tall main deck, while cars can use lower decks or hoistable decks that can be raised out of the way.

Deck data (illustrative) Main deck Upper / car deck
Lanes × length 4 × 90 m (360 LM) 6 × 80 m (480 LM)
Lane width ≈ 3.0 m ≈ 2.2 m
Free height 4.8 m 2.0 m
Maximum axle load 12 t 3 t

These figures are examples only. Real data comes from the ship's loading plan and documents; other ship types can be compared with the ship types tool.

Main deck capacity example: 14 trucks of 12 m with a 0.5 m gap fore and aft use 14 × 12.5 = 175 LM. The remaining 360 − 175 = 185 LM can take 4.5 m cars with a 0.5 m gap, that is 185 ÷ 5.0 = 37 cars at one car per truck lane. If the deck can be re-laned into narrower car lanes, car capacity goes up.

Axle loads, lane loads and point loads

Vehicle deck strength is given as a maximum axle or wheel load plus a uniform load per lane or per m². There are three checks:

  • Axle load: the heaviest axle of each vehicle against the deck limit. A 25 t three-axle truck with a 10 t rear axle is fine on a 12 t deck, but an overloaded truck with a 14 t axle is not.
  • Lane load: weight divided by the length occupied. A 25 t truck 12 m long gives about 2.1 t per lane metre, which is compared with the ship's lane rating.
  • Point loads: landing legs of unaccompanied trailers, trestles and tracked vehicles concentrate load on small areas; use spreader plates or beams.

In Indonesia, declared truck weights often differ from actual weights. Weighing at the port and understanding the ODOL rules help prevent overloading. Try an axle check with the axle load calculator; the concept is explained in truck axle load and GVW. For uniform loads, use the deck load calculator.

Ramps and vehicle movement

Stern ramps, quarter ramps and internal ramps each have their own SWL, and often only one heavy vehicle may be on a ramp at a time. Ramp angle changes with tide and draft; low or long vehicles can ground if the angle is too steep. At ferry ports, the ship's ramp rests on a fixed berth or a movable bridge that has its own load limit.

Vehicle movements are directed by deck crew. The space between vehicles has to be enough for the crew to fit lashings, for drivers and passengers to get out safely and for firefighting access. Minimum distances follow the Cargo Securing Manual, the operator's procedures and the authority's rules.

Loading and discharge order

The loading order decides how quickly the ship can discharge and how stable it stays during operations:

  1. Discharge port: vehicles for the first port go near the ramp or in drive-through lanes, later ports further in.
  2. Weight and height: trucks and heavy vehicles on the low, strong main deck; cars on upper decks.
  3. Heel during loading: heavy vehicles are spread port and starboard in turn. Many Ro-Ro ships use heeling tanks to keep the ship upright as vehicles drive on.
  4. Drive-off direction: on ships without drive-through, heavy vehicles are reversed in so they can drive out forwards.
  5. Dangerous goods go in designated areas, never just any empty lane.

After loading, check GM, trim and draft with the basic GM calculator. Large open vehicle decks are very sensitive to water on deck, for example firefighting water, because of the large free surface effect. Scuppers and drains must work.

Vehicle lashing

Vehicle securing follows the ship's Cargo Securing Manual, the CSS Code annex on wheel-based (rolling) cargoes (Annex 4) and the IMO guidelines on securing arrangements for road vehicles on Ro-Ro ships (Res. A.581(14)). Those guidelines cover the spacing of deck securing points and the securing points on the vehicles themselves. Common practice:

  • Handbrake on, engine off and vehicle in gear.
  • Lashing chains or webbing from the vehicle's securing points to deck points, at suitable angles in both the transverse and longitudinal directions.
  • Unaccompanied trailers supported on trestles, not just their landing legs.
  • Wheel chocks for heavy vehicles and in bad weather.

Lashing needs and strength can be estimated with the lashing calculator; the general principles are in cargo lashing and securing.

Dangerous goods on Ro-Ro decks

Vehicles or trailers carrying dangerous goods must be declared before loading. The IMDG Code covers stowage and segregation in Ro-Ro spaces, while SOLAS chapter II-2 covers fire protection, ventilation and electrical equipment there. Key ideas: closed and open Ro-Ro spaces are treated differently, some classes are allowed only on open decks, and vehicles with fuel in their tanks are a fire consideration in their own right. Electric vehicles are a newer concern because battery fires are hard to extinguish, and the guidance is still evolving. The basics of classification are in the IMDG Code glossary entry.

Common mistakes

  • Working out capacity from lane metres alone, when free height, lane width and axle load often bite first.
  • Using declared weights without checking, so KG, draft and deck loads look lighter on paper than in reality.
  • Putting all heavy trucks on one side because they arrived early, then relying on the heeling tanks.
  • Filling an empty lane with a dangerous goods vehicle without checking that the area is approved.
  • Leaving lashing until after departure, when the first roll outside the breakwater often comes sooner than expected.

Shore-side planning

A shore-side Ro-Ro planner needs a vehicle list with actual weights, a lane allocation and axle-load and stability checks before the ship arrives. STOWAGE.ID Vessel Stowage and the Ro-Ro stowage page help build lane and loading-order scenarios ashore. It is decision support: the ship's class-approved loading computer and stability booklet remain the official reference, and the master has the final say. For heavy vehicles on landing craft, see the LCT loading guide.