CPP control fault under load

Anonymized vessel case. A controllable-pitch propulsion fault appeared only after clutch engagement. With the clutch out, the command path behaved normally; with the clutch engaged, ahead response was lost while only limited astern response remained.

We compared clutch-out and clutch-in operation, followed the command path and measured the solenoid outputs in neutral and when commanded. The active coil current was approximately 800 mA, the opposite coil fell to approximately zero, and both coils sat at approximately 160 mA in neutral. These values matched the sister unit.

Solenoid coils were changed, cabling was checked, and the complete valve assembly was swapped with a known working sister-unit assembly. The fault behaviour remained. Manual pitch movement was also checked to confirm that the mechanism could move, although with abnormally high resistance.

The PLC command path and electrical drive to the proportional solenoids were behaving consistently with the healthy sister unit. Cabling, the solenoid coils and the swapped valve assembly did not explain the state-dependent fault.

This materially reduced the remaining fault area and shifted the investigation away from the electrical command chain toward the downstream hydraulic/mechanical side of the pitch system.

The investigation ruled out several plausible electrical and valve-side causes with comparative measurements rather than assumption. It prevented further replacement of components that were demonstrably behaving like those on the healthy sister unit.

With the electrical/control scope completed, the remaining fault area was handed over to the vessel’s hydraulic / high-pressure piping specialist for further investigation, as that work was outside the agreed Ventus scope.

For propulsion-control faults, the useful result is not always an immediate component replacement. Proving which parts of the command chain are healthy can be the decisive step, especially when the fault appears only under clutch load or another specific machinery state.