Cargo Lashing

A cargo lashing is a high-tenacity polyester webbing strap with a ratchet tensioner in its run and a hook at each end, bought to stop a load moving rather than to lift it. It is rated in lashing capacity – LC – not in working load limit, and the figure printed on the label is the load it can hold, not the load it can carry. The heaviest in this range is rated at 10 t (10,000 daN).

The reason one person can secure a load of that size with a strap that weighs a couple of kilos is the ratchet. A handle, a drum and a pawl turn a hand force measured in hundreds of newtons into a tension measured in hundreds of deca-newtons, and the tension is what presses the load onto the deck. That multiplication is the whole mechanism – and the thing most often misunderstood when a lashing is bought on price alone.

Three parts, and only one of them is complicated

A lashing is a system of three parts, and the weakest of them sets the rating. The band carries the tension; the hooks (or the absence of them) decide what it can be attached to; the ratchet decides how much tension one person can put in.

• The band. Flat woven polyester, dyed to a colour that identifies the size in most ranges. It has to be stiff: a lashing band is specified by elongation as well as by strength, because a band that stretches under load lets the cargo move and then shocks everything in the system when it catches.
• The hooks. Double-J, flat hook, S-hook or ring. The hook is what meets the lashing point on the vehicle or the container floor, and a hook that does not sit fully in its point is the commonest cause of a lashing coming loose in service.
• The ratchet. A lever, a drum and a pawl with a release. It is the only part with moving parts, it is the part that gets abused, and it is the part that decides whether the tension you intended is the tension you got.

The ratchet, or how a hand does the work of a crane

The old image for it is four ounces moving a thousand catties, and that is an accurate description of what a ratchet does. Three things combine.

• The handle is a lever. The grip is several times further from the pivot than the point where the band enters the drum, so the force at the drum is several times the force at the hand.
• The drum is a winch. Every stroke winds a few centimetres of band onto the drum, and the band is already lying along the load: the tension rises with each stroke rather than with the distance travelled.
• The pawl holds what has been won. A toothed pawl drops into the ratchet wheel between strokes, so the tension does not run back while the handle is returned. This is why the tension can be built in steps by one person, and why it stays there after they walk away.

The number that comes out of this is the standard tension force, STF – the pre-tension a person can put into the strap with the handle, and it is marked on the label next to the LC. STF matters because of what it produces: friction. A lashing does not hold a load by wrapping it; it holds it by pressing it onto the deck, and the friction between load and deck is proportional to that pressure. Where the surface is slippery, or wet, or the load is on steel rather than on timber, the answer is an anti-slip mat under the load rather than another turn on the handle.

LC is not WLL – and the two must never swap places

A webbing sling and a lashing strap can look almost identical, are woven from the same fibre on the same looms, and are rated in different ways for different duties. The confusion between them is the reason this page has a table instead of a sentence.

There is a practical consequence that catches people out at service counters: a 10 t lashing capacity is not the same as a 10 t lifting sling, and a customer who asks for “a 10 tonne strap” may mean either. Ask which duty, and the rest of the specification follows from the answer.

What the label has to say

Every lashing sold from this works carries a sewn label, and the label is not decoration – it is the only thing that distinguishes a rated assembly from a strap.

• LC – the lashing capacity of the complete assembly, hook to hook, not of the band alone.
• STF – the standard tension force, i.e. what the handle should produce, so the operator knows what “tight” means on that size.
• Length and width – the length convention matters, because a lashing is bought to reach between two points.
• Maker and standard. Where a market or a customer requires a particular standard – the European lashing strap standard is EN 12195-2 – say so on the enquiry; a label is printed to the order, not to a default.
• A date or a batch, where the customer’s own system requires traceability on the strap rather than on the delivery note.

How the number is arrived at

The weight of the cargo is the start of the calculation, not the answer. Three factors decide how much restraint a consignment needs, and they are the three questions we ask before quoting a strap.

• Mass and direction. The load has to be held against acceleration in three directions. The forward case is normally the worst – the rules of most road markets size a lashing against a deceleration of the order of 0.8 g – so a 20 t load is being held against roughly 16 t of forward force before any factor is applied.
• Angle. A strap that runs at an angle to the deck gives a component of its tension vertically: ma 45 degrees roughly seven tenths of the tension is doing useful work, and the rest is pulling the load sideways against the opposite strap. The shallower the angle, the more of the LC is wasted.
• Friction. The coefficient between load and deck decides how much of the restraint comes free. Timber on timber is helpful; steel on steel is not, and a steel coil on an aluminium deck is the case that needs mats as well as straps.

The arithmetic is short – required restraint divided by what one strap contributes at its angle, rounded up – and we run it for the consignment rather than selling a number of straps by habit. Send the load, the deck and the route and the count comes back with the LC of the strap that does it.

Hooks, and what they are asked to hold

The end fitting is where a lashing is attached, and the fitting has to match the point rather than the other way round. Four are usual in this range.

• Double-J hook – two curved prongs that drop into a lashing point or over a rail; the general-purpose end for flatbeds and container corner fittings.
• Flat hook – a wide flat hook that sits on the edge of a load bed or a rail without marking it; common on flatbed trailers.
• S-hook – a simple hook for a ring or an eye; cheap, quick, and the one most easily bent open by a load that shifts.
• Ring or no hook – a ring end for a shackle or a ratchet-to-ratchet arrangement, and the plain end for a strap that is passed around the load and tensioned against itself.

Where a cargo lashing is used

The same article is sold into four settings, and each one stresses a different part of it.

Length is part of the specification too, and it is the line most often got wrong by eye: a lashing is bought to reach from a hook to a rail, and the usable length is shorter than the band once the ratchet and the hooks have taken their share. A 10 m strap does not give 10 m of reach – quote the distance between the two points and the length follows.

The band underneath

The webbing is woven in this works on needle looms, from high-tenacity polyester yarn: warp along the length carrying the load, weft across it, both selvedges woven closed so the band does not run. Lashing band is normally woven denser and stiffer than sling band of the same width, because the requirement is not only strength but resistance to stretch – and because a lashing is handled far more often than a sling, along a truck bed, over a rail, through a hook.

Five ways a lashing fails

Failures in service are rarely about the strength of the band. They are about how it was fitted, and about the parts that were not inspected.

• Over-tension. A ratchet can put far more tension into a band than the load needs, and the excess crushes the cargo, stretches the band and pre-loads the hooks. Tension to the STF, then check.
• A hook that is half in. A J-hook sitting on the edge of a lashing point rather than in it will come out when the load moves – and it will do so at the worst moment, which is braking.
• No edge protection. A sawn timber arris, a coil edge or a fabricated steel corner cuts webbing. A sleeve or a corner protector is part of the lashing, not an accessory.
• Worn ratchet teeth. A pawl that has worn or a spring that has weakened will release under vibration. This is the failure that gives no warning and cannot be seen from outside the drum.
• The wrong duty. A lifting sling used as a lashing, or a lashing used to lift. Two ratings, two markings, two different jobs; the swap is a fatal-practice, not a shortcut.

Nānā, care and the end of life

Inspect before every trip and formally at the interval the operator’s system sets. The conditions that remove a lashing from service are specific rather than a matter of judgement.

• Cuts, snags, tears and abrasion anywhere in the band, and especially where it passes over an edge.
• Stitching at the hook and at the ratchet end – broken or worn rows are the failure that happens first.
• Heat or chemical damage – glazed, stiff or discoloured fibre, or a band that has been in contact with acid, caustic or solvent.
• The ratchet – worn teeth, a weak or missing pawl spring, a bent lever, a drum that does not turn freely.
• The label – if LC or STF cannot be read, the assembly cannot be matched to a load and comes out of service.

Store coiled, clean and dry, off the floor and out of sunlight; a lashing left on a truck bed for a season is not the lashing that was delivered. Wash with water and a mild detergent, never with solvents, and dry before it goes back in the cab.

Six lines on the enquiry

A lashing is specified by the load it has to hold, not by the length on the shelf. Six lines settle it.

Frequently asked questions

Where each question goes on this site

This page owns the lashing. Hāpai ʻia, webbing and the hardware each have a page of their own, and they are the better place to settle those questions.

• Webbing sling – the lifting article, and the full mode-factor table
• White flat webbing sling – the same band, undyed
• Single use lifting slings – one journey, then written off
• 3 tonne flat webbing sling – the most-bought lifting size
• Lifting devices – hooks, shackles and the hardware at the eye
• Cargo lifting net – when the load is loose rather than packed