Rigging Calculator —
DNV-ST-N001 & EN 13889

What is rigging design for an offshore lift?

Rigging design sizes the slings, shackles and padeyes that connect a lifted object to a crane. For offshore work, the chain of calculations starts with a Dynamic Amplification Factor (DAF) that captures inertial loads from vessel motion, then propagates the amplified load through the sling legs, into the shackle, and finally as a bearing load on the padeye pin.

• DAF (Dynamic Amplification Factor): Multiplier applied to static lift weight to account for motion. DNV-ST-N001 Table 16-3 gives DAF as a function of lift weight, sea state and lift type.
• Sling-leg tension: The amplified load divided across the legs and projected along each sling axis. A skew factor accounts for unequal sharing in 3- and 4-leg arrangements.
• Shackle de-rating: EN 13889 shackles lose capacity when loaded off the in-plane axis. Side-loads above 15° require a working-load reduction.
• Pin bearing: Where the shackle pin contacts the padeye hole, the projected bearing stress must stay below the Eurocode 3 limit 1.5·f_y/γ_M0.

Which standards govern offshore rigging design?

• DNV-ST-N001:2023 — Marine Operations and Marine Warranty. §16 covers lifting operations including DAF selection, skew factor, sling-leg sizing, and the matrix of weight/sea-state combinations.
• EN 13889:2008+A1:2014 — Forged steel shackles for general lifting purposes. Annex A specifies de-rating factors for side-loaded shackles in 15° / 45° / 90° bands.
• EN 1993-1-8 — Eurocode 3 Part 1-8: Design of joints. §3.13 gives bearing resistance for pin connections as 1.5·f_y/γ_M0.
• NORSOK R-002:2017 — Lifting equipment. Annex E provides worked examples consistent with the DNV-ST-N001 methodology and is the Norwegian Continental Shelf reference.

How the chain of checks runs

• 1. DAF DNV-ST-N001 §16.2.6 — Onshore lifts use 1.10. Inshore sheltered use 1.20. Offshore uses Table 16-3 base DAF (2.00 for ≤100 t down to 1.50 for >1000 t) multiplied by a sea-state factor for H_s > 1 m.
• 2. Sling-leg tension DNV-ST-N001 §16.5.4 — T = W·DAF·skew / (n·cos α). Skew defaults to 1.0 for n ≤ 2 (statically determinate) and 1.25 for n = 3 or 4 (one leg carries more due to fabrication tolerances).
• 3. Shackle side-load de-rating EN 13889 Annex A — Allowable load = 1.00 × WLL for 0–15°, 0.70 × WLL for 15–45°, 0.50 × WLL for 45–90°. Above 90° the shackle is not permitted under load.
• 4. Pin bearing EN 1993-1-8 §3.13 — σ_b = F / (d_pin · Σt) where Σt = t_plate + 2·t_cheek. Resistance f_b,Rd = 1.5·f_y/γ_M0.
• Utilisation ratios — Each check returns UR = applied / allowable. UR ≤ 1.0 → PASS, > 1.0 → FAIL. Address fails by increasing leg count, reducing α, upsizing the shackle or thickening the padeye.