What is a marine slip ring?

A slip ring sealed and built for shipboard and offshore service: salt-laden air, spray or immersion, vibration and often hazardous areas. Typical uses are crane slews, winches, cable and hose reels, radar and FPSO turret swivels. Marine winch units carry thousands of volts and hundreds of amps at slow speeds, and hybrid versions add fibre optic channels for data.

What is an FPSO swivel?

An FPSO weathervanes around a moored turret, so power, control signals and fibre must cross the rotating joint between turret and vessel. Electrical swivels do this at low, medium or high voltage. Moog's published range spans units with up to 600 signal passes to high-voltage swivels up to 145 kV, protected as Ex d, Ex de or Ex p for hazardous areas.

Do offshore slip rings and actuators need ATEX certification?

Only if they are installed in a classified hazardous area, but on production platforms, drilling rigs and FPSOs much of the deck is classified. Equipment for those zones must be certified for the zone, gas group and temperature class: ATEX in the EU, the EPS Regulations 2016 in Great Britain and IECEx internationally. Safe-area equipment does not need it.

Which slip ring suits a cable reel?

Cable and hose reels turn slowly and reverse often, and the slip ring sits at the drum axis carrying the reeled cable's power and signals. Pick it on voltage, current per circuit, any data or fibre channels, speed and ingress rating. For outdoor quay and deck reels, sealed IP65 to IP68 units are normal, and some combine RF or fibre channels.

How do I protect motion components from salt and spray?

Choose the right ingress rating for the location (IP66 for deck spray, IP67 or IP68 for immersion), 316 stainless or suitably coated housings, sealed connectors, and breathers or heaters where condensation forms. Avoid dissimilar metals in contact. Ask suppliers which salt-mist and vibration tests their units have passed and against which standard.

What should I send for a marine or offshore enquiry?

Send the machine and its location on the vessel or platform, the hazardous-area zone, gas group and temperature class, circuits with voltage and current, data and fibre channels, rotation speed or stroke and force, ingress rating, ambient temperature range, vibration and shock levels, classification society and any approval required, and design life.

Marine slip rings, actuators and motors for offshore

Specify Motion technical library · Updated 30 October 2026 · How we prepare our content

In short:Marine and offshore motion parts must survive salt, water, vibration and, on many decks, explosive atmospheres: slip rings carry power, fibre and data through crane slews, cable reels, radar and FPSO turret swivels, while sealed actuators, motors, encoders and gearboxes drive deck machinery. Start from the location on the vessel, its hazardous-area zone and ingress needs, then size the motion.

Typical requirements

Marine winch slip ring voltage and current (examples)	Up to 7,200 V AC; 7–125 A per pass; up to 1,000 A total (Moog)
Winch slip ring speed	Typically 5–100 rpm continuous (Moog marine models)
FPSO swivel ratings	Up to 600 signal passes; medium-voltage to 36 kV; high-voltage to 145 kV (Moog)
FPSO swivel protection types	Ex d, Ex de or Ex p
Ingress for exposed deck equipment	IP66 to IP68
Hybrid slip rings	Up to 52 single-mode or multimode fibres with power (Moog)
Deck hatch actuator (example)	316 stainless, IP67M, 12/24 V DC, up to 2,300 N

Machinery we specify motion for

Ship and offshore cranes
Hose and cable reels
Marine winches and seismic gun winches
Marine surveillance and navigation radar
FPSO turret and swivel systems
Pod propulsion and steering
Deck hatches, doors and antenna actuators
Seismic and oceanographic handling equipment

What marine and offshore service demands

Marine and offshore equipment combines three hard environments: corrosion from salt air and spray, constant vibration and ship motion, and, on production platforms, drilling rigs and FPSOs, explosive atmospheres. Moog lists the scope of the work: floating production systems, ROVs, seismic and oceanographic equipment, shipbuilding and vessel integration, marine pod propulsion and drive and control solutions. Most of these rotate something continuously and need power and data across that rotation, so slip rings matter more here than in almost any other industry.

Where motion components sit on a vessel or platform

Machine	Motion	Main components
Ship and offshore crane	Slew, luff, hoist	Slew slip ring, absolute encoders, gearboxes, motors and drives
Cable and hose reel	Slow, reversing rotation	Reel slip ring, tension-controlled motor, level-wind
Marine winch, seismic gun winch	Rotation under load	High-voltage slip ring, often with fibre and air passages
Radar	Continuous antenna rotation	Slip ring with RF or data channels, azimuth encoder
FPSO turret	Vessel weathervanes around the turret	Electrical and optical swivel stack, Ex-protected
Pod propulsion	Steering rotation of the pod	High-power slip ring and steering drive
Hatches, doors, antennas	Short strokes	Stainless sealed linear actuators

Marine slip rings: winches, reels and cranes

Marine winch slip rings are built for high voltage and current at slow speed. Moog’s winch slip ring comparison runs from the model 180 (7 A per pass, 100 A total, 1,000 V AC, 100 rpm) to the model 129 (125 A per pass, 7,200 V AC, 50 rpm), with the model 159 carrying up to 1,000 A total. Its product guide adds hybrid units with up to 52 single-mode or multimode fibres alongside up to 7.4 kV and 720 A, and a seismic gun winch unit with 23 circuits, 1,000 V DC, 120 A, 100 Mbit/s Ethernet and an air passage at 210 bar, turning at up to 20 rpm.

Tolomatic shows the companion motion on a reel: a cable cylinder guiding cable onto a spool on an ocean oil rig. See marine slip rings, high-current slip rings, slip rings for cable reels, slip rings for cranes and slewing and fibre optic rotary joints.

Radar, FPSO swivels and mooring

Marine radar rotates continuously. Schleifring describes a marine radar slip ring that powers the radar, helps cool the antenna and carries received signals to the ship’s computer, on a radar it says can track more than 1,000 targets at up to 2,000 km. Our pages on slip rings for radar antennas and marine mooring cover the detail.

FPSO turret swivels are the largest rotating joints offshore. Moog’s guide lists low-voltage electrical and optical swivels with up to 600 signal passes at 6 A and 600 V, up to 20 power passes at 200 A and 1 kV, and up to 52 fibre passes; power swivels with up to 50 passes; medium-voltage swivels to 36 kV; and high-voltage swivels to 145 kV. Protection is Ex d, Ex de or Ex p, because the turret sits in a hazardous area.

Deck actuators: electric instead of hydraulic

Hydraulics have long dominated deck machinery, but every hydraulic line on deck is a leak and maintenance point, and a spill at sea is an environmental incident. For hatches, doors, antenna adjusters, level-winds and smaller handling equipment, electric actuators remove the power unit and hoses and need only a cable. Stainless IP67M in-line actuators at 12 or 24 V DC suit yachts and work boats; servo-driven roller-screw actuators carry the heavier loads of deck machinery. The trade-off is that the electric actuator must be sealed, sized for duty and shock, and, in classified areas, certified. See linear actuators and the hydraulic to electric actuator guide.

Environment checklist for marine components

Ingress: IP66 for deck spray and washdown, IP67 or IP68 where parts can be submerged or sit in bilge areas.
Materials: 316 stainless or marine-grade coatings, no dissimilar metals in contact, sealed connectors.
Condensation: heaters or breathers in enclosures that see daily temperature swings.
Vibration and shock: engine-room vibration, slamming and snatch loads on cranes and winches; ask which tests the supplier has run.
Temperature: from Arctic decks to engine rooms; check lubricants, seals and electronics at both ends.
Approvals: classification society requirements, plus Ex certification where the location is zoned.

Pod propulsion and steering

In a podded or azimuthing thruster, the propulsion motor or its drive line sits in a unit that steers through 360°. Power, monitoring signals and sometimes cooling or lubrication services must cross that steering rotation, which is why rotary joints matter here. Moog lists marine pod propulsion among its marine applications and says the highest demands are placed on the reliability of propulsion components. For a component specifier the key inputs are the propulsion power and voltage, the number of monitoring circuits, whether the steering is continuous or limited, the service interval the vessel can accept, and the classification society’s requirements for propulsion machinery.

Hazardous areas on offshore decks

Much of a production platform or FPSO is classified. In Great Britain, HSE explains that DSEAR requires zoning, and equipment for zoned areas must meet the Equipment and Protective Systems Regulations 2016, which implement ATEX Directive 2014/34/EU. R. STAHL’s marking guide maps the zones: Zone 0 needs category 1G (EPL Ga), Zone 1 needs 2G (Gb) and Zone 2 needs 3G (Gc). Internationally, the IECEx scheme certifies equipment by type testing plus factory quality assessment, and a product not on its online certificate system is not IECEx certified. Offshore wind shares many of the same reel, crane and corrosion problems; see renewable energy.

Worked example: specifying a crane slew slip ring

An offshore pedestal crane needs, through its slew:

3-phase 690 V power at 150 A for the hoist and luff drives
230 V auxiliary power for lights and heaters at 16 A
24 V DC control circuits and safety signals
Gigabit Ethernet for cameras and the crane control network

Steps:

Power rings: 150 A per phase rules out small precious-metal units; a carbon-brush high-current design is the natural fit.
Speed: crane slews are slow; confirm the maximum continuous speed in rpm and whether the crane can slew continuously or has limited rotation.
Data: gigabit Ethernet next to 690 V motor power needs a shielded data section or a fibre channel. Many designers move the camera network to fibre to avoid the problem.
Environment: IP66 or better for deck spray, heaters for condensation, and materials for salt.
Zone: if the crane house sits in Zone 2, the slip ring needs at least category 3G equipment or must sit in a protected enclosure; a Zone 1 location needs 2G, for example a flameproof Ex d unit.
Approvals: the crane will be built to a classification society’s lifting appliance rules, so ask which documentation the society needs for the slip ring.

Typical pitfalls

Specifying a safe-area part for a classified deck. Check the zone before anything else.
Running Ethernet next to motor power in the same slip ring without separation.
Ignoring condensation. A sealed IP68 box with no heater or breather can fill with water from inside.
Mixed metals in fasteners and housings that corrode at the joint.
No plan for maintenance at sea. Carbon-brush slip rings are serviceable; make sure the access and spares exist.

What to send an engineer

Send the machine and its location, hazardous-area zone, gas group and temperature class, circuits and data, speed or stroke and force, ingress rating, temperature range, vibration and shock, the classification society and design life. Our engineers can propose slip rings, actuators, motors, encoders and gearboxes to match.

Marine slip rings for cranes, reels and radar

Slip rings are the most marine-specific motion part. Crane slews, cable and hose reels, winches, radar antennas and FPSO turrets all need power and data across continuous rotation. Heavy carbon-brush units carry hundreds of amps at slow speed and are easy to maintain at sea; sealed IP64 to IP68 units suit deck spray and wet machinery; RF and fibre channels serve radar and data-heavy cranes; flameproof units are certified for hazardous areas. Specify each circuit's voltage and current, data, fibre and RF channels, speed, bore, ingress rating, temperature, hazardous-area zone and the vessel's classification requirements.

Offshore and ship cranes: power, control and Ethernet through the slew
Cable and hose reels: power and signal at the drum axis
Marine radar: power and RF or data across the antenna rotation
Winches: high-voltage power to towed or lowered equipment
Hazardous decks: flameproof slip rings for classified zones