1. Inputs

Load

Mass M [kg] Total weight of the load (including rigging hardware attached). Length L [m] Side-view length of the load. Width W [m] Depth into the page. Height H [m] Base to top.

Centre of gravity

defaults to geometric centre

x_cog [m] auto LEFT end of load to COG, along L. y_cog [m] auto Above BASE. Uniform beam ≈ H/2.

Lift points (Crane 1 & Crane 2)

default to load top corners

x_lp1 [m] auto Crane 1 lug — horizontal position from LEFT end. y_lp1 [m] auto Crane 1 lug — height above BASE. Default top edge = H. x_lp2 [m] auto Crane 2 lug — horizontal. Must be > x_lp1. y_lp2 [m] auto Crane 2 lug — height above BASE.

Landing supports (S₁ & S₂)

default to load bottom corners

x_s1 [m] auto S₁ left support — horizontal position. y_s1 [m] auto S₁ height above BASE. Default bottom edge = 0. x_s2 [m] auto S₂ right support — horizontal position. y_s2 [m] auto S₂ height above BASE.

Static share + compliance baseline

non-synchronised, 2 cranes — compliance default

	Crane 1 (LP1)	Crane 2 (LP2)
`F`_static (lever rule)	25.00 t	25.00 t
Compliance baseline (× 1.20)	30.00 t	30.00 t

For two cranes where motions are not synchronised, each crane shall be sized for 20 % greater than the calculated share. This is the compliance default unless a documented designed lift is applied — see §4. Clause provenance in §6 References.

2. Geometry

Dynamic raise tolerance `α`

0°5°10°15°

In-plane tilt during raise (typ. 2–5°).
Live — geometry & chart update with the slider.
Out-of-plane motion excluded — see §5 / §6.

Per-crane factor `F`/`F`_static vs `α` (0–15°)

3. Results

Scenario	Crane 1 factor (× `F`_1,static)	Crane 2 factor (× `F`_2,static)
Static (`α` = 0°)	×1.000	×1.000
Dynamic raise (`α` = 2.5°)	×1.011	×1.011
Landing — R support (S₂) first (`α` = 2.5°)	×1.011	—
Landing — L support (S₁) first (`α` = 2.5°)	—	×1.011
Geometric worst factor → used by §4	×1.011	×1.011

Factor basis (geometric only). Each factor = F_scenario / F_static. The chart in §2 plots these same factors continuously over α. The rated-capacity chart already includes the single-crane hoist dynamic factor — do not multiply this geometric worst factor by a hoist dynamic factor again, or you will double-count. The multi-crane asynchrony margin is applied separately in §4. Clause provenance in §6 References.

4. Per-crane factored load

Designed-lift acknowledgement

Designed lift documented — competent person + third-party review recorded in lift plan.

Off → governing per crane uses the compliance baseline from §1 (F_static × 1.20). On → the engineering lift below replaces the baseline. Clause provenance in §6 References.

5. Method of calculation

Derived geometry

a₁ = |x_cog − x_lp1| = 4.00 m a₂ = |x_cog − x_lp2| = 4.00 m span = a₁ + a₂ = 8.00 m h = H − y_cog = 1.00 m (vertical drop from lift plane to COG) X_s1 = |x_cog − x_s1| = 4.00 m ; X_s2 = |x_cog − x_s2| = 4.00 m

Static load share — lever rule about the COG (ropes plumb)

F_1,static = M · a₂ / span F_2,static = M · a₁ / span

Dynamic raise — in-plane tilt up to `α` (ICSA N002 Annex 1)

shift = h · tan α = 0.044 m (horizontal COG swing for the worst tilt) F_1,max = M · (a₂ + shift) / span (COG swings toward Crane 1) F_2,max = M · (a₁ + shift) / span (COG swings toward Crane 2, opposite tilt)

Each formula represents the worst direction of tilt for that crane; they are not simultaneous.

Sequential set-down — landing scenarios (ICSA N002 Annex 2, α-augmented)

shift = h · tan α (COG horizontal swing during asynchronous descent — same form as raise) If S₂ touches first (load pivots about S₂): F₁′ = M · (X_s2 + shift) / (a₁ + X_s2) ; S₂′ = M − F₁′ If S₁ touches first (load pivots about S₁): F₂′ = M · (X_s1 + shift) / (a₂ + X_s1) ; S₁′ = M − F₂′

Real-world landings are almost never perfectly symmetric — one end touches first, intentionally or otherwise. The COG-swing term h·tan α captures the asynchronous descent before touchdown, consistent with the in-plane asynchrony allowance used for the raise. With α = 0 the formulas reduce to the pure ICSA N002 Annex 2 expressions.

Overall geometric worst case per crane

C_n,worst = max(F_n,static, F_n,max, F_n′_landing) factor_n = C_n,worst / F_n,static Governing = the crane with the larger factor (drives the sizing margin)

Symbol legend

M: total mass of load [kg]
L, W, H: load length / depth / height [m]
x_cog, y_cog: COG position in side view (origin = bottom-left of load) [m]
x_lp1, x_lp2: lift-point positions on the top edge [m]
x_s1, x_s2: landing-support positions [m]
α: in-plane raise inclination tolerance [°]
a₁, a₂: horizontal lever arm from COG to each lift point [m]
h: vertical drop from lift-point plane down to COG [m]
X_s1, X_s2: horizontal lever arm from COG to each support [m]

6. References

AS 2550.1-2011 Cranes, hoists and winches — Safe use — Part 1: General requirements §6.28 Multiple hoist or crane operation; §6.28.3 Capacity requirements (non-synchronised: +20 % for 2 cranes — applied as baseline in §1 / §4); §6.28.5.5 Synchronisation of crane and crab motions + NOTE 3 (electronic synchronisation methods); §6.27 + §1.4.4 Designed lift — competent person authoring + third-party review (acknowledged in §4 to unlock designed-lift reduction).
ISO 12480-1:2024 Cranes — Safe use — Part 1: General §8.1 Lifting with multiple cranes or multiple hoists — esp. §8.1.1 a–f (planning requirements), §8.1.3 Supervision (appointed person), §8.1.4 Coordination of crane motions ("…there will always be some variation due to differences in response to the motion controller and the setting and efficiency of the braking system")
ICSA N002 (Apr 2016) Lifting a Load with Several Mobile Cranes (Multiple Crane Lifts) — FEM industry consensus Annex 1 — FEM dynamic allowance (the h·tan α model implemented here); Annex 2 — sequential set-down asymmetry
AS 5221.1:2021 Cranes — Design principles for loads and load combinations — Part 1: General (ISO 8686-1:2012, MOD) §6.1.2.1 hoist dynamic factor φ₂ = φ_2,min + β₂·v_h — single-crane structural-design factor used by the crane manufacturer; already included in the published rated-capacity chart. Not applied here to avoid double-counting.
AS 1418.1:2021 §4 Cranes, hoists and winches — General requirements §4.2 defers all load combinations to AS 5221.1. Standalone dynamic factor clauses from AS 1418.1—2002 §7.4–7.9 superseded.
AS 1418.5:2013 §4.1.2.5 Cranes — Mobile cranes (EN 13000:2010, MOD) Defers to FEM 5.004:1994 and ISO 8686-1:1989 for working load factor Φ. Same single-crane-structural concept as AS 5221.1 φ₂; baked into chart.

Scope: in-plane asynchrony only (load pitching about the lift line). Out-of-plane motion (slew / travel / luff at different rates causing off-plumb hoist ropes and boom side-load) is excluded from this calc — controlled procedurally per ISO 12480-1 §8.1 ("hoist ropes shall remain vertical") and §8.1.3 supervision.