Floating Crane Barge

Overview

A floating crane barge is a non-propelled or limited-propulsion marine platform that carries a heavy lifting crane on a flat-deck pontoon hull. It performs lifts that exceed the reach or capacity of shore cranes: setting bridge spans, installing offshore structures, salvaging wrecks, and handling outsized cargo that no quay crane can reach. The vessel described here is a 90 m revolving crane barge rated for a 500 t main hook, built around nine major subsystems: the Barge Hull / Pontoon, the Crane Structure, the Hoisting System, the Luffing System, the Slewing Drive, the Power Pack & Engine Room, the Ballast & Stability System, the Mooring & Anchoring System, and the Operator Control Cabin.

The defining engineering problem is that a large suspended load applies an overturning moment to a floating body that has no fixed foundation. Everything in the design works to keep that moment within the stability the hull can supply. The hull provides buoyancy and a wide waterplane for righting moment, the ballast system shifts water to counter list and trim, and the load-moment system limits how far the crane may reach for a given weight.

Barge Hull and Pontoon

The Barge Hull / Pontoon is a welded steel box pontoon, 90 m long and 36 m wide, with a 7.5 m depth and a double bottom. The main working surface is 20 mm Main Deck Plating supported by a grillage of Transverse Web Frame transverse webs on 600 mm spacing and Longitudinal Stiffener bulb-flat stiffeners, with deep Deck Girder members spreading the crane base reactions across the structure. The Double-Bottom Plating forms a double bottom that protects against grounding and houses ballast.

Eight Watertight Bulkhead walls subdivide the hull into watertight compartments, so flooding of any one compartment does not sink the vessel. Twelve Ballast Tank units, each fitted with a Tank Manhole Cover, an Air Vent Head, and a Sounding Pipe, hold up to 8,500 t of seawater. The crane is seated on a Crane Foundation Ring ring, a heavy rolled forging welded into the deck grillage that carries the entire crane load into the hull.

Crane Structure

The Crane Structure is a revolving design. A triple-row Slew Bearing Ring of 4.5 m pitch diameter, with a geared Slew Inner Race (Geared) and a cylindrical Slew Roller Set, carries the axial, radial, and moment loads while letting the upper works turn. Above it sits the Revolving Upper Carriage, a welded box-girder turntable that mounts the boom, the winches, and the Machinery House.

The Main Lattice Boom is a 60 m tubular lattice of four Boom Chord Member corner members tied by Boom Lacing into a triangulated truss. At the tip, the Boom Head Sheave Block carries cast Wire-Rope Sheave wheels on rolling bearings. The boom is suspended by Boom Pendant Bar eye-bars running to the A-Frame / King Post back mast. A Counterweight Block of concrete-filled steel boxes, about 250 t, balances the boom moment so the slew ring sees a smaller net overturning load.

How Lifting Works

The Hoisting System raises and lowers the load. The Main Hoist Winch spools 36 mm Hoist Wire Rope onto a grooved Hoist Winch Drum, driven through a planetary reducer by two Hydraulic Drive Motor units and held by a spring-applied Band Holding Brake. The rope reeves through the boom-head sheaves and the Main Hook Block, an eight-fall block ending in a forged Ramshorn Crane Hook on a Hook Swivel Bearing. Multiple falls divide the load across the rope so a 500 t lift is carried on rope tensions each well below the breaking strength. For light, fast work the Auxiliary Hoist Winch drives the single-fall Auxiliary Hook Block.

Reach is changed by the Luffing System. The Luffing Winch hauls Luffing Wire Rope reeved between the boom head and the Equalizer Gantry equalizer, raising the boom to shorten the radius or lowering it to extend out. Shorter radius means higher capacity, because the overturning moment is load times radius. A Boom Back-Stop back-stop buffers the boom against over-luffing in a gust. Rotation comes from the Slewing Drive: four Slew Drive Unit packs, each a floating-crane-barge-servo-motor feeding a planetary gear and a Slew Pinion, mesh the ring gear, while Slew Holding Brake units park the upper works.

How Stability and Ballasting Work

A floating crane cannot ignore where the load sits. As the boom swings out and the hook takes weight, the combined centre of gravity shifts toward the load and the barge heels. The Ballast & Stability System counters this by moving water. Two Ballast Pump units, fed through a Ballast Ring Main ring main with remote Ballast Butterfly Valve valves, flood or empty individual tanks to set the right list and trim before and during a lift. The Anti-Heel Transfer Unit transfers water rapidly between wing tanks to hold the deck level while the crane swings a load across the beam.

The Stability Computer (Loadicator) reads tank levels from the floating-crane-barge-pressure-sensor transmitters and the live crane load, then displays righting arm, draft, and trim in real time so the operator never crosses the approved stability limit. Twelve tanks and roughly 8,500 t of ballast give the operator enough water to balance the full rated moment with margin in reserve.

Materials and Construction

The hull is built from AH36 and EH36 grade shipbuilding steel, plate thicknesses graded from 14 mm side shell up to 20 mm deck where the crane loads concentrate. The lattice boom uses high-tensile S690 tube for the chords to keep the structure light at a long reach. Slew bearing races and the Slew Pinion are case-hardened alloy steels for contact fatigue life. Hooks, pendant bars, and pins are forged alloy steel, proof-tested before service. Wire ropes are galvanized for marine corrosion resistance, and the Hydraulic Oil Cooler in the hydraulic plant uses titanium plates against seawater. The whole vessel is built and surveyed to a classification society crane-vessel notation.

Power and Control

The Power Pack & Engine Room houses two Diesel Generator Set sets, each a turbocharged Marine Diesel Engine driving an AC Alternator, feeding a Main Switchboard. Generated power runs the Hydraulic Power Unit hydraulic power unit, whose Variable Hydraulic Pump units supply 350 bar oil to every winch and slew motor through the Control Valve Block. The operator works from the Operator Control Cabin, commanding hoist, luff, and slew through two Master Joystick Controller controllers, watching the Load-Moment Indicator load-moment indicator and Marine Camera feeds.

Variants and Use Cases

Crane barges fall into two broad families. Revolving types like this one turn a full circle and place loads anywhere within reach, which suits piecemeal construction and salvage. Sheerleg types use a fixed A-frame boom that luffs but does not slew, trading flexibility for higher capacity in a lighter structure, often above 1,000 t. Stationary positioning is handled by the Mooring & Anchoring System, with Mooring Winch winches, Stockless Anchor anchors, and Anchor Chain holding station against current and the reaction of each lift.

In service these vessels install offshore wind turbine foundations and topsides, lift precast bridge segments into place over water, recover sunken vessels and aircraft, load and discharge project cargo too heavy for port cranes, and support harbour and breakwater construction. Their value is reaching jobs that have no land access and lifting weights that fixed cranes cannot.