How is cargo secured and lashed on a ship?

Cargo that breaks adrift at sea can hole the ship, kill crew, destroy stability or go overboard, so securing is treated as seriously as navigation. A ship in a seaway rolls, pitches and heaves, and the accelerations this produces try to slide, tip and lift every item aboard. The forces are greatest at the ends of the ship and high above the waterline, and a stiff ship with a large metacentric height rolls hard and fast, which raises them further, so stowage position and the ship's loading condition matter as much as the lashings themselves.

The method depends on the cargo. Containers lock to the ship and to each other with twistlocks between corner castings, with lashing rods and turnbuckles tensioning the lower tiers of deck stacks; the permitted stack weights and lashing patterns come from the ship's approved arrangements, and exceeding stack weight or using damaged fittings invalidates them. Heavy lifts, project cargo, vehicles and steel are secured with chains, wires or web lashings led to strong points of known strength and tensioned, with timber dunnage to spread loads and fill gaps. Break-bulk and palletised goods are blocked, chocked and lashed within the hold so nothing can start to move, because movement begets movement.

The governing documents are the ship's approved Cargo Securing Manual, which specifies the equipment, its maximum securing load and the arrangements for the cargo types the ship carries, and the IMO Code of Safe Practice for Cargo Stowage and Securing, whose Annex 13 provides the method for calculating whether a proposed arrangement can withstand the expected forces. Securing is therefore a calculation, not a judgement of how tight a lashing feels: the number, angle and strength of lashings must add up against the predicted accelerations, and steep lashing angles do little against sliding just as flat ones do little against tipping.

Practical discipline for the voyage: - Inspect securing gear before use and quarantine anything worn, bent or corroded; never mix fittings of different type and strength in one stack. - Re-tension lashings within a day of sailing, since cargo settles, then check regularly and before forecast heavy weather. - In heavy weather, ease the ship's motion by altering course and speed rather than sending crew onto a rolling deck; working among container lashings in a seaway has killed people. - Log inspections and any re-securing carried out.

If cargo does shift, slow down, bring the motion under control, and treat re-securing at sea as a planned, risk-assessed operation, escalating to the company and treating any stability effect as an emergency.