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Vehicles and other rolling cargo carried on ro-ro decks and pure car and truck carriers (PCTCs) are not self-securing — a parked car or trailer relies entirely on its handbrake, wheel chocks, and applied lashings to resist the dynamic forces of a rolling and pitching ship. Unlike stowed break-bulk or containerised cargo, each unit typically sits on rubber tyres on a steel deck, giving very little natural friction resistance. Lashing practice on ro-ro decks is governed primarily by the IMO CSS Code (Code of Safe Practice for Cargo Stowage and Securing) and by the vessel-specific Cargo Securing Manual (CSM), which SOLAS makes mandatory.
Ro-ro decks are fitted with recessed lashing points at regular intervals, commonly the “cloverleaf” or “pot” pattern — a shaped socket recessed flush with the deck plating so vehicle wheels can pass over it without damage. A lashing hook, D-ring, or turnbuckle end fitting engages the socket. Deck fittings are rated by the shipyard/manufacturer for a maximum securing load (MSL), and that rating — together with the MSL of the lashing itself and of the vehicle’s own securing points — sets the working limit of the whole arrangement. The weakest link in the chain governs.
| Type | Typical use | Notes |
|---|---|---|
| Web (synthetic strap) lashing | Cars, light vans, small vehicles | Ratchet tensioner; lighter, faster to apply, some elasticity absorbs shock loads but can creep/stretch over a voyage |
| Chain lashing | Heavy trucks, mafi trailers, high-and-heavy units, static/project cargo | Turnbuckle or lever tensioner; higher MSL, minimal stretch, standard for heavier units |
The CSM sets out, for each vehicle/cargo category carried, the minimum number of lashings and their required angle and arrangement, derived from a balance-of-forces calculation against the assumed transverse, longitudinal, and vertical accelerations the vessel can experience at sea. Heavier units and units carried higher in the ship (further from the centre of roll) require more lashings, arranged to resist sliding, tipping, and — for high-sided units — racking. The officer supervising securing follows the CSM’s specific instructions for the vessel and voyage rather than a generic rule of thumb.
Lashings work together with, not instead of, the vehicle’s own means of resisting movement. Standard practice for driven vehicles: handbrake applied, transmission left in gear (or “park” for automatics), and wheel chocks placed fore and aft of at least one wheel set before lashings are tensioned. This combination means the lashings are resisting dynamic sea forces on top of a vehicle that is already static, rather than being the sole restraint.
Non-self-propelled ro-ro cargo — containers, break-bulk units, project cargo — is commonly carried on Mafi (roll trailers), which are themselves driven aboard by a terminal tractor and then lashed to the deck like any other rolling unit. Static high-and-heavy cargo without wheels is often supported on timber or steel trestles to spread deck loading and to bring securing points to a workable height, then lashed and additionally shored/chocked against sliding.
A ship underway generates combined roll, pitch, and heave accelerations that are far higher than anything experienced alongside. Roll in particular produces large transverse accelerations on cargo stowed away from the centreline and high in the ship. Web lashings can stretch under repeated cyclic loading, and turnbuckles can work loose from vibration; both effects reduce tension over a voyage. This is why the CSM requires periodic rounds to check and re-tension lashings, particularly after the vessel has experienced heavy weather.
The IMO CSS Code sets out general principles for stowage and securing of cargo, including the balance-of-forces methodology in its Annex 13 used to calculate required securing arrangements from assumed accelerations. SOLAS Chapter VI, Regulation 5, and Chapter VII require every ship carrying cargoes other than solid/liquid bulk cargoes to carry a Cargo Securing Manual, approved by the flag State or a recognised organisation acting on its behalf. The CSM is ship-specific: it lists the actual lashing points, fittings, and equipment fitted on that vessel, their individual and combined MSLs, and the securing arrangements required for the cargo types the ship is approved to carry.
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