KH 680
ZF Marine KH 680 — Controllable Pitch Propeller (CPP/Verstellpropeller).
Inspector Detail
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Common issues
- Blade seal (O-ring) leakage into the hub, often first seen as rising water content in hub oil samples
- Oil distribution box (OD box) wear causing sluggish or erratic pitch response
- Hub oil contamination from seawater ingress through the stern tube seal area
- Blade carrier bearing wear leading to increased blade play and vibration at certain pitch angles
- Pitch feedback (follow-up) transmitter drift causing indicated pitch to disagree with actual blade angle
- Cavitation erosion and pitting on blade leading edges
- Sticking or slow-moving spider/crosshead linkage inside the hub
- Loose or corroded blade flange bolts
Inspection checklist
- Draw hub oil sample and check water content, particle count, and viscosity
- Check hub oil level and top-up trend against previous readings
- Function-test full ahead-to-full-astern pitch travel and time the response
- Compare pitch indicator reading against actual blade angle where accessible
- Visual inspection of blades for cavitation erosion, pitting, and leading-edge damage
- Check blade seal condition where accessible (dry dock or underwater inspection)
- Inspect OD box for external oil leakage and shaft seal condition
- Check blade bolt torque witness marks for movement
- Verify hub oil low-level and pitch feedback alarms against class-approved setpoints
- Inspect stern tube seal for wear/leakage that could contaminate hub oil
Service intervals
| Hub oil sample analysis | every 3-6 months or per maker manual |
| Hub oil change | per maker manual, typically every 2-4 years or on contamination |
| OD box seal inspection | at each dry docking |
| Blade seal renewal | typically at dry docking intervals (2.5-5 years) or on condition |
| Pitch feedback calibration check | annually |
| Full pitch range function test | every 3-6 months |
Typical wear limits
| Hub oil water content (alarm threshold) | commonly limited to well under 1% by volume across CPP makers - use the specific hub's maker limit, not a generic figure |
| Blade bolt stretch/torque | check against the maker's specified torque-turn or stretch values - OEM-specific, no generic figure applies |
| Pitch feedback deviation from actual blade angle | typically investigated once deviation exceeds a few degrees - confirm the exact alarm setpoint in the ship's pitch control system |
Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.
Critical spares
- Blade O-ring seal set
- OD box shaft seal
- Hub oil (maker-specified type and quantity)
- Blade bolts and locking elements
- Pitch feedback transmitter/follow-up unit
- Servo piston seals
Safety
- Hub is under internal oil pressure - do not open without following the maker's de-pressurisation procedure
- Pitch mechanism can move unexpectedly if the hydraulic system is not isolated and pressure released
- Work aloft/overside on blades requires proper access and lifting precautions
- Confirm the shaft is locked/blocked before any work inside the OD box or on blade linkages
Class survey
Falls under shafting/Continuous Machinery Survey (CMS) regimes for classed vessels; hub oil sampling and blade condition at dry docking are typical survey items. Tailshaft/CPP hub examination interval depends on the class's shaft survey scheme (conventional vs CMS) and any stern tube arrangement in place.
Components & Design
Component data being added…
Technical Data
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Common failures & inspection points
Check for oil losses at the pitch cylinder and at all hydraulic connections. Perform hydraulic pressure measurement. Normal pressure should correspond to the manufacturer's specification (typically 150-200 bar).
Visual inspection of all propeller blades for cracks, particularly at the blade-hub connection and at the trailing edges. Perform ultrasonic or magnetic particle crack detection. Material: nickel-aluminium bronze must be tested for fatigue cracks.
Check the double seal between hub and propeller base for wear and contamination. Perform colour test with tracer fluid to identify leakage. For KS series, double seal is standard.
Check play in the blade bearings by manual movement inspection. Check for detached metal particles in the hydraulic fluid. Perform fluid analysis. Bearing wear leads to increased play and reduced pitch accuracy.
Visual inspection for corrosion and pitting on the nickel-aluminium bronze hub and blades. Perform grinding samples for thickness measurement. Check cathodic protection systems. Remove salt deposits and clean surfaces.
Type-general inspection and maintenance points for this equipment category — not model-specific.
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