ISO 4306-7:2005 (MOD) is the section of the crane terminology standard that covers floating cranes, specifying the dedicated terms and definitions for these vessels. A floating crane is an engineering vessel equipped with a crane for lifting operations, widely used in port handling, marine construction, bridge building, and offshore engineering projects.

Floating Crane Classifications

The floating crane classifications covered by ISO 4306-7:2005 (MOD) include: by hull configuration — monohull floating cranes (a single hull, simple structure, lower cost, commonly used for small-to-medium capacity units) and catamaran floating cranes (two hulls joined by a connecting structure, offering better stability and larger deck area, typically used for heavy-lift units). By propulsion — self-propelled (equipped with its own power for independent navigation and positioning) and non-self-propelled (requiring tugboat assistance).

By lifting capacity — small-to-medium floating cranes (50–500 t), heavy-lift floating cranes (500–3,000 t), and ultra-heavy-lift floating cranes (above 3,000 t). The growth of offshore wind farm installation and maintenance has driven the development of ultra-heavy-lift floating cranes, with capacities now reaching 5,000 t and above. By boom type — fixed-boom (boom locked at a set angle) and luffing-boom (boom angle adjustable for greater working flexibility).

Main Structure and Key Terminology

Key terms covered by the standard: overall length — the maximum length of the floating crane hull. Molded breadth — the maximum width of the hull. Molded depth — the vertical distance from the baseline to the main deck. Draft — the vertical distance from the baseline to the waterline (both no-load and full-load draft). Freeboard — the vertical distance from the main deck to the waterline. Metacentric height (GM value) — the distance from the center of gravity to the metacenter, a core parameter for assessing floating crane stability.

Working radius — the horizontal distance from the hook to the slewing centerline of the floating crane. Lifting height — the vertical distance between the highest and lowest hook positions (measured both above and below the waterline). Derricking speed — the rate at which the boom angle changes. Slewing angle — the rotation range of the slewing platform (typically 360° full rotation). Positioning accuracy — the ability of the floating crane to maintain its horizontal position during operations.

Stability and Positioning

Stability is the most critical safety indicator for floating cranes. The standard addresses two types of stability: intact stability — the ability of the floating crane to withstand wind, waves, and lifting loads under normal conditions (no watertight compartment damage), requiring a righting moment ≥ overturning moment × 1.4 (operating condition) or × 1.5 (transit condition). Damage stability — the ability of the floating crane to remain afloat without capsizing after any single watertight compartment is flooded.

Positioning methods: anchor mooring — the floating crane is secured in position using multiple anchors (typically 4–8) and anchor chains, suitable for nearshore and port operations in water depths ≤ 50 m, with positioning accuracy of ±5 m. Dynamic positioning (DP) — the vessel automatically maintains its position and heading using thrusters and propellers, suitable for deepwater operations and applications requiring precise positioning (e.g., offshore wind installation).

Operating Limits and Inspection Requirements

Operating limits specified by the standard: lifting operations must cease when wind speed ≥ Force 6 (13.8 m/s); operations must stop when wave height ≥ 1.5 m (small-to-medium floating cranes) or ≥ 2.5 m (heavy-lift floating cranes); no operations when visibility is < 1,000 m; exercise caution when current speed ≥ 3 knots. The latest weather and sea-state forecasts must be obtained before each operation.

Inspection requirements: floating cranes must undergo an annual stability verification (accounting for the effects of retrofits and equipment changes on the center of gravity), a dry-dock inspection every 5 years (for underwater hull maintenance), and a full stability recalculation and inclination test after any major modification. Safety equipment — floating cranes must be equipped with life-saving appliances, fire-fighting equipment, communication equipment, and navigation signal devices. Kelude offers related products and technical services.

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