Convert lashing force ratings and estimate top-over sliding, idealized direct sliding, or general US tiedown minimums. These calculations require a complete load-securing assessment; they do not certify a safe arrangement.
Lashing Capacity Formula
Use the manufacturer’s labelled lashing capacity (LC). The nominal 2:1 breaking-force relationship below applies to suitable rated reusable webbing and chains; other materials and uses have different ratios. A breaking-force conversion cannot certify an unknown assembly’s LC.
- Where LC is the lashing capacity (a force rating), typically marked in daN (or kN)
- MBL (or MBS) is the minimum breaking load/strength (force), in the same units
For the stated reusable-webbing/chain assumption only, estimate LC as MBL/2. One daN = 10 N ≈ 1.02 kgf; this is force, not cargo mass. Top-over sliding uses STF and factors 1.25 forward or 1.10 sideways/rearward. Direct sliding counts equally sharing effective legs with β measured from the chosen resisting direction. US aggregate WLL credits full WLL for opposite-side over/around tiedowns and half WLL for same-side or vehicle-to-cargo tiedowns; both aggregate WLL and length minimums apply.
What is a Lashing Capacity?
Definition:
Lashing capacity (LC) is the maximum rated restraining force a lashing assembly is designed to provide in use (typically stated in daN or kN). It is a force rating—not a mass/weight value in kg—and the actual securing effect depends on angles, friction, and the securing method.
How to Calculate Lashing Capacity?
Example Problem:
The following nominal example assumes suitable rated reusable webbing or chain and the applicable 2:1 ratio. Verify the actual manufacturer rating and weakest attachment before use.
First, determine the minimum breaking load/strength (MBL/MBS) from the lashing label or manufacturer. In this example, the lashing has an MBL of 10,000 daN.
Next, use the relationship above to estimate the lashing capacity.
LC ≈ MBL / 2
LC ≈ 10,000 / 2
LC ≈ 5,000 daN (≈ 50 kN)
