In short:Shipboard motion components fail from salt, water and shock long before they wear out, so specify sealing, materials and shock qualification first: IP66 or IP67 for exposed parts, salt fog testing, IEC 60945 or MIL-STD-167-1 vibration, and MIL-DTL-901E high-impact shock where the ship requires it. Then size the motors, slip rings and encoders for the job.
Typical requirements
| Mast pan-tilt payload and slew (examples) | 1.8–9 kg at 0.01–60 °/s; up to 68 kg at 0.005–60 °/s |
|---|---|
| Stabilisation (maritime pan-tilt example) | Under 2 mrad RMS |
| Wind rating (maritime pan-tilt example) | 100 knots operational; 125 knots survival |
| Exposed equipment sealing | IP67 typical for mast-mounted positioners |
| Winch slip ring rating | 7–125 A per pass; 1 kV to 7.2 kV AC; 5–100 rpm |
| Shipboard vibration (MIL-STD-167-1 Type I) | Exploratory 4–33 Hz; endurance at least 2 h at 33 Hz for mounted equipment |
| Operating temperature (examples) | −40 °C to +70 °C (maritime pan-tilt) |
Machinery we specify motion for
- Mast-mounted EO/IR and surveillance positioners
- Radar and navigation antennas
- Stabilised sensor and deck mounts
- Boat davits and stores cranes
- Towed-body and mooring winches
- Launch and recovery systems for boats and unmanned vehicles
- Watertight doors, hatches and vents
- Below-deck valve and handling actuators
Warships and naval auxiliaries carry motion systems from the masthead to the waterline: radar and communication antennas, mast-mounted EO/IR and surveillance positioners, stabilised mounts for sensors and deck equipment, davits and boat-handling cranes, towed-body and mooring winches, hatches and doors, and launch and recovery systems for boats and unmanned vehicles. Every one of them shares three enemies: salt, water and shock. Getting those right decides whether a motor, slip ring or encoder lasts a commission or a few months.
Mast-mounted sensors and positioners
Mast-mounted positioners pan and tilt cameras, thermal imagers, laser rangefinders and small antennas, usually with continuous pan through an integrated slip ring. Published examples show the range:
- General Dynamics OTS’s Vector 20 carries 1.8–9 kg with continuous pan, 0.01–60 °/s, under 2 mrad RMS stabilisation, a 9-channel slip ring, IP67, −40 °C to +70 °C, and is rated for 100-knot operational and 125-knot survival winds, with vibration to IEC 60945.
- Quickset’s TAURUS R carries up to 68 kg balanced at 0.005–60 °/s with 0.05° repeatability and continuous pan via slip ring; a marine configuration meets IP67, and vibration and shock are to MIL-STD-810H Methods 514.8 and 516.8.
Components inside: direct-drive or low-backlash geared motors, absolute encoders on each axis, a sealed slip ring and a drive. For specifying the motors, encoders and stabilisation, see our EO/IR gimbal page; for pan-tilt slip rings, see CCTV and pan-tilt slip rings.
Radar and navigation antennas on the mast use integrated slip ring and RF rotary joint assemblies; SPINNER lists sea-water-resistant housings on some of its rotary joints. See radar pedestals and antenna positioners.
Stabilised mounts
Stabilised mounts keep a sensor or deck equipment level or pointed while the ship rolls and pitches. Ship motion is low frequency but large amplitude, which shifts the design emphasis compared with airborne gimbals: high continuous torque to fight sustained roll, large angular range, good thermal margin, and robust sealing. Size motor torque from payload inertia, imbalance and the required correction rate at the worst sea state, then check gear or direct-drive stiffness and encoder resolution against the pointing budget. See frameless torque motors, gearboxes and absolute vs incremental encoders.
Davits, cranes and winches
Boat davits, stores cranes, towed-body winches and launch and recovery systems for unmanned vehicles are heavy, intermittent-duty machinery exposed to green water and spray. They use rugged motors with brakes, gearboxes, absolute encoders for position and payout, and slip rings on any drum that carries a powered or data cable. Moog’s winch slip rings range from 7 A per pass at 1 kV and 100 rpm (Model 180) to 125 A per pass at 7.2 kV AC and 50 rpm (Model 129), with fibre optic options for data. For a launch and recovery system for an underwater vehicle, see military UUVs and AUVs. Electric conversions of hydraulic davit and hatch functions are covered in the hydraulic to electric actuator guide.
Hatches, doors and below-deck actuators
Watertight doors, hatches, vents, valves and handling equipment below deck are increasingly electrified. Below deck the environment is kinder on salt but harsher on shock, because equipment mounted to the hull structure sees the full shock input, and space for maintenance is tight. Choose linear actuators with self-locking screws or brakes so they hold under shock and ship motion, specify a manual override for every safety-related door or hatch, and agree end-of-stroke and position feedback for the ship’s monitoring system. Exposed weather-deck actuators need the same sealing and salt fog evidence as mast equipment. How to size a linear actuator covers force, speed and duty.
Marine slip rings
Shipboard slip rings need sealed, corrosion-resistant housings, condensation control and connectors that survive salt. Specify the IP code under IEC 60529, materials (stainless, marine-grade aluminium with suitable anodising, or bronze), and how moisture is kept out of the brush chamber during long idle periods: seals, desiccant breathers or dry-air purge. Read how to specify a slip ring, marine slip rings and marine and mooring slip rings.
Salt fog, ingress and materials
- Salt fog. Test to the tailored MIL-STD-810H Method 509 procedure or the ship specification. Ask for the duration and the post-test functional check, not just “passed”.
- Ingress. IP67 is common for mast-mounted positioners. IP68 immersion conditions are agreed between maker and user, so state depth and duration if you need it.
- Materials. Avoid dissimilar-metal contact or isolate it; specify compatible fasteners and coatings, and UV-resistant cable jackets and seals.
Shock: MIL-DTL-901E context
MIL-DTL-901E, issued in June 2017 to supersede MIL-S-901D, sets high-impact shock requirements for equipment on surface ships and submarines. Equipment is Grade A (essential to the ship’s safety and combat capability) or Grade B (not essential, but must not become a hazard to people or Grade A items). Under the earlier 901D, the lightweight shock machine covered items up to about 250 kg (550 lb), the medium weight machine up to about 3,400 kg (7,400 lb), and heavier equipment went on a floating shock platform. For motion components the practical consequences are robust mounting, retention of rotors, brushes and encoder discs under shock, and brakes and gearing that do not release a load.
Vibration and EMC
- Vibration. MIL-STD-167-1 Type I environmental vibration includes an exploratory sweep from 4 to 33 Hz and, for mounted equipment, an endurance test of at least two hours at 33 Hz; Type II covers internally excited vibration of rotating machinery. IEC 60945 applies to navigation and radiocommunication equipment.
- EMC. MIL-STD-461H, released in April 2026, extends CE101 applicability to 20 kHz for surface ships and submarines and changes some shipboard limits. UK programmes may call up DEF STAN 59-411. Shipboard environments are dense with high-power radar and communications, so radiated susceptibility matters as much as emissions.
- Export control. Naval systems and their specially designed components may be controlled; see the defence and security overview.
Typical pitfalls
- Treating IP68 as a marine rating.
- Forgetting condensation inside slip rings and gearboxes that sit idle.
- Testing to MIL-STD-810 shock when the ship requires MIL-DTL-901E.
- Mixing stainless fasteners with aluminium housings without isolation.
- Under-sizing positioner torque for icing and wind at the masthead.
Send your location on the ship, loads, environment and shock grade, and our specialist engineering and supply partners can propose marine slip rings, motors, encoders and drives.
Marine slip rings for shipboard systems
Shipboard slip rings fail from salt, water and condensation long before they wear out. Specify the IP code under IEC 60529, housing material and finish, connector sealing, and how moisture is kept out of the brush chamber during long idle periods: seals, desiccant breathers or dry-air purge. Remember that IP68 immersion conditions are agreed between maker and user and say nothing about salt fog or UV. Winch and davit drums need high-voltage power passes and often fibre; mast positioners need compact sealed rings; radar and navigation antennas need rings integrated with RF joints. Ask for salt fog test duration and the post-test functional check.
- Towed-body and mooring winches: power and fibre across the drum
- Mast positioners: sealed rings for continuous pan
- Radar and navigation antennas: rings with RF rotary joints
- Davits and cranes: slewing power and control rings
- Launch and recovery systems: hybrid electrical and fibre rings
Available through our supply network
All slip rings →Specify slip rings for naval shipboard systems →
Direct-drive torque motors for stabilised mounts
Ship motion is low frequency but large amplitude, so a stabilised mount needs high continuous torque to fight sustained roll, a large angular range and good thermal margin, rather than the very high bandwidth of an airborne gimbal. Direct-drive torque motors remove backlash and give smooth correction; size them on payload inertia, imbalance and the correction rate at the worst sea state, and check RMS torque over a long roll cycle inside a sealed housing. Mast-mounted heads also see high wind loads. Specify bore, envelope, bus voltage, temperature range and a brake for parking, and ask how the motor and its mounting retain the rotor under shock.
- Stabilised sensor mounts: direct-drive roll and pitch correction
- Mast-mounted positioners: smooth pan and tilt
- Deck equipment mounts: levelling axes
- Antenna positioners: backlash-free tracking
Available through our supply network
All frameless and torque motors →Specify frameless and torque motors for naval shipboard systems →
Servo motors for davits, winches and positioners
Davits, stores cranes, towed-body winches and launch and recovery systems are heavy, intermittent-duty machinery exposed to green water and spray. They use brushless servo or induction motors with spring-applied brakes and gearboxes, often in sealed enclosures or below-deck machinery spaces with drive shafts to the deck. Specify torque and speed for lifting and paying out, holding with power off, the duty cycle, and the IP rating and finish for the location. For geared positioners, size the motor from the gearbox output torque at the worst wind and icing case. Check how motor mounts and brakes behave under the ship's shock requirement, so a load is never released.
- Boat davits: hoist and luffing drives with brakes
- Towed-body winches: payout and recovery drives
- Launch and recovery systems: controlled hoisting
- Geared mast positioners: pan and tilt servo motors
Available through our supply network
All servo and stepper motors →Specify servo and stepper motors for naval shipboard systems →
Gearboxes for winches and shipboard positioners
Winch, davit and positioner gearboxes must hold loads under shock and ship motion and keep salt and water out through long idle periods. Specify output torque, peak and shock torque, holding requirement, radial load on pinions and sprockets, backlash for pointing axes, and service life. Choose stainless or suitably coated housings for exposed locations, with sealed shafts and breathers that do not pump moist air in as the temperature swings. Right-angle gearheads keep drives compact in tight machinery spaces; low-backlash hollow reducers suit mast-mounted positioners. Avoid dissimilar-metal contact between stainless gearboxes and aluminium structures, or isolate it.
- Winches and davits: high-torque reduction
- Mast positioners: low-backlash hollow reducers
- Stores cranes: slewing drives
- Exposed deck equipment: corrosion-resistant gearheads
Available through our supply network
All gearboxes and harmonic drives →Specify gearboxes and harmonic drives for naval shipboard systems →
Encoders for mast positioners and winch payout
Mast positioners need absolute angle on each axis for pointing and reporting, and winches need payout and drum position for safe launch and recovery. Choose encoders sealed for the location, with materials and connectors that survive salt and condensation. Capacitive and inductive designs tolerate moisture and dirt better than open optics. Specify resolution, accuracy, interface, temperature range and shock rating, and check that discs, rotors and readheads are retained under the ship's shock requirement, which may be MIL-DTL-901E rather than MIL-STD-810. Next to high-power radar and communications, ask for radiated susceptibility data as well as emissions.
- Mast positioners: absolute pan and tilt angle
- Winches: drum position and cable payout
- Stabilised mounts: axis feedback
- Davits: arm position and limits
Available through our supply network
All encoders and feedback →Specify encoders and feedback for naval shipboard systems →
Marine linear actuators for hatches and doors
Watertight doors, hatches, vents, valves and handling equipment are increasingly electrified. Below deck the environment is kinder on salt but harsher on shock, because equipment on the hull structure sees the full shock input. Choose actuators with self-locking screws or brakes so they hold under shock and ship motion, and specify a manual override for every safety-related door or hatch. Agree end-of-stroke and position feedback for the ship's monitoring system. Marine-grade stainless actuators suit enclosed and sheltered spaces; check their rated temperature range against the location. Exposed weather-deck actuators need the same sealing and salt fog evidence as mast equipment.
- Watertight doors and hatches: powered operation with manual override
- Vents and dampers: remote open and close
- Below-deck valves: electric actuation
- Handling equipment: high-force roller-screw actuators
Available through our supply network
All linear actuators →Specify linear actuators for naval shipboard systems →
Servo drives for shipboard positioners and winches
Shipboard drives run from the ship's AC or DC supply, sit in machinery spaces or sealed enclosures, and must ride out shock and vibration. Specify the supply, continuous and peak current, feedback interfaces, network, Safe Torque Off for maintenance and temperature range. Winch and davit drives need controlled lowering and regeneration handling. Positioner drives need smooth low-speed control and enough peak current for gusts. Shipboard environments are dense with high-power radar and communications, so radiated susceptibility matters as much as emissions; MIL-STD-461H changed some shipboard limits in 2026. Ask how drive modules are retained in their racks under shock.
- Mast positioners: smooth stabilisation and pointing control
- Winches and davits: controlled hoisting and lowering
- Launch and recovery systems: coordinated multi-axis drives
- Hatches and doors: actuator motor control
Available through our supply network
All servo drives →Specify servo drives for naval shipboard systems →
Standards to have in view
- MIL-DTL-901E (high-impact shock tests for shipboard machinery, equipment and systems)
- MIL-STD-167-1 (mechanical vibrations of shipboard equipment)
- MIL-STD-810H (environmental engineering and laboratory tests)
- MIL-STD-461H (control of electromagnetic interference; supersedes MIL-STD-461G)
- IEC 60945 (maritime navigation and radiocommunication equipment: general requirements and tests)
- IEC 60529 (IP codes)
- DEF STAN 00-35 (environmental handbook for defence materiel)
- DEF STAN 59-411 (electromagnetic compatibility)
Which standards apply depends on the end product and its market. Your engineer will confirm what the component itself needs to meet.
Frequently asked questions
What is MIL-DTL-901E?
MIL-DTL-901E, dated June 2017 and superseding MIL-S-901D, is the US Navy detail specification for high-impact shock testing of machinery, equipment, systems and structures on surface ships and submarines. It verifies that equipment survives shock loadings from weapons effects or environmental mechanical shock. Equipment is graded A (essential to the ship's safety and combat capability) or B (not essential, but must not become a hazard).
What is the difference between lightweight, medium weight and heavyweight shock tests?
They are test categories chosen by equipment weight and mounting. Under MIL-S-901D the lightweight shock machine took items up to about 250 kg (550 lb) including fixture, the medium weight machine up to about 3,400 kg (7,400 lb), and heavyweight items were tested on a floating shock platform with underwater charges. Check MIL-DTL-901E and the ship specification for the current categories and limits.
Is IP68 enough for a deck-mounted actuator or slip ring?
IP68 means the product survives continuous immersion under conditions agreed between maker and user, but it says nothing about salt fog, UV, ice or green water impact. For exposed shipboard equipment specify the IP code, the salt fog test and duration, materials and finishes, connector sealing and, for rotating seals, behaviour after long periods without movement. Many mast-mounted positioners are rated IP67.
Which slip rings suit shipboard use?
Marine slip rings with sealed, corrosion-resistant housings, appropriate IP rating and condensation control. Deck winches and davits use high-voltage winch slip rings such as Moog's Model 129 to 180 range, from 1 kV to 7.2 kV AC. Mast-mounted pan-tilt units integrate smaller sealed slip rings; radar and navigation antennas use integrated slip ring and rotary joint assemblies.
What vibration standard applies to shipboard equipment?
US Navy equipment is commonly tested to MIL-STD-167-1, which has Type I environmental vibration (an exploratory sweep from 4 to 33 Hz, a variable frequency test and an endurance test) and Type II internally excited vibration for rotating machinery. Navigation and communication equipment often follows IEC 60945. Your ship or class specification decides which applies.
What should I send for a shipboard motion component enquiry?
Send the equipment's location on the ship (mast, open deck, below deck), payload and load per axis, speed and accuracy, wind and sea state ratings, IP and salt fog requirements, temperature range, vibration and shock standards with grade and class, EMC standard, supply type and voltage, slip ring circuits and data, materials restrictions and the maintenance interval you can accept.
Sources
- EverySpec: MIL-DTL-901E shock tests, high-impact shipboard machinery
- Wikipedia: MIL-S-901
- Sealevel: meeting and exceeding standards for shipboard equipment
- General Dynamics OTS: Vector 20 stabilised maritime pan-tilt system
- Quickset Defense: TAURUS R positioner datasheet
- Moog: winch slip rings model comparison
- SPINNER: air traffic control rotary joints catalogue
- In Compliance: MIL-STD-461H, a review
Figures are summarised from the sources above and from manufacturers' published data on the date shown. Always confirm against the current datasheet for your exact part.