System Overview: Sperry Marine MK 27 (Mark 27) Gyrocompass
The Sperry Marine MK 27 (Mark 27) is a legendary compact electromechanical master gyrocompass developed for naval patrol craft, workboats, ocean-going tugs, and merchant vessels. Designed with a direct optical compass card viewing window and an internal liquid-immersed gyrosphere, the MK 27 established Sperry’s benchmark for compact mechanical reliability before the advent of microprocessors.
The system features an external static inverter or motor-generator power unit, mechanical gimbal suspension with oil dampers, a follow-up servo motor, and step-by-step repeater transmission capability that continues to operate reliably on retrofitted and preserved vessels globally.
Technical Specifications: Sperry MK 27
| Parameter | Specification Details |
|---|---|
| Model Designation | Sperry Mark 27 Master Gyrocompass (Naval & Commercial) |
| Rotor Type | High-inertia balanced induction gyro rotor running in evacuated sphere |
| Settling Time | Approx. 3 hours from cold start |
| Accuracy | ±0.5° static accuracy; ±1.0° dynamic accuracy in moderate sea conditions |
| Repeater Transmission | 35 V DC / 70 V DC step transmission (6 steps per degree) to bridge repeaters |
| Input Power | 115 V AC, 60 Hz or 24 V DC through dedicated static inverter power supply |
| Mounting Configuration | Bulkhead or pedestal binnacle with internal shock-absorbing coil springs |
| Operating Temperature | -15°C to +55°C wheelhouse operating range |
Spare Parts, Overhaul Kits & Subassemblies
| Component | Part Number | Description |
|---|---|---|
| MK 27 Gyrosphere | MK27-SPHERE-ASY | Balanced liquid-floating gyrosphere (reconditioned with fresh bearings) |
| Supporting & Damping Liquid | MK27-LIQ-KIT | Electrolyte supporting solution with anti-corrosion additives (1L) |
| Follow-Up Servo Motor | MK27-FUP-MTR | Reversible follow-up drive motor with precision pinion gear |
| Step Transmitter Assembly | MK27-STEP-TX | Mechanical step commutator switch transmitting heading to repeaters |
| Static Inverter Power Unit | MK27-INV-PWR | Replacement solid-state inverter generating 3-phase gyro rotor power |
| Gimbal Shock Damper Springs | MK27-DAMP-SET | Matched set of 4 stainless vibration-damping springs and rubber snubbers |
| Slip Ring Contacts | MK27-BRUSH-ASY | Phosphor bronze brush assembly for continuous 360° azimuth rotation |
Seanav Restoration & Maintenance Services
Seanav Marine offers specialized refurbishment and field repairs for legacy Sperry MK 27 installations:
- Container Descaling & Fluid Replacement: Complete disassembly of the inner chamber, electrode contact cleaning, and filling with fresh lab-grade supporting solution.
- Rotor Bearing Rebuilding: Precision dismantling of the evacuated sphere, dynamic spin balancing, and lubrication with instrument grease.
- Step-to-NMEA Heading Converters: Installing modern digital step converters that read the MK 27 step output and produce NMEA 0183 ($HEHDT) for modern AIS and ECDIS units.
- Bench Calibration: Full 24-hour drift test on our rate table to verify settling zero and follow-up sensitivity.
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