DP Mini Guide: Motion & Wind Sensor Failure (MRU/VRU)

Crew Connect DP Academy · Mini Guide 26

Motion & Wind Sensor Failure (MRU/VRU)

Topic: Sensors · Sub-topic: Motion & Wind Sensors  ·  Level: DPO  ·  Read time: 8 min

1. What / Why / How

Motion Reference Units (MRU/VRU) measure the vessel's actual motion (roll, pitch, heave), used to correct other sensor readings for vessel movement. Wind sensors feed the DP system's feed-forward thrust calculation directly. Both carry genuinely different information than position or heading alone — degraded data from either can distort the whole picture even while PRS and gyro look perfectly healthy.

2. Recognition / Risk / But

Erratic wind readings, while actual vessel motion shows no such variation, risk the DP system applying thrust corrections that don't match real conditions. But: before assuming the DP system is being actively misled, check whether the wind-sensor voting/selection logic has already detected the inconsistency and is handling it.

3. Now / What next / Decision / Why

If the system has already down-weighted the erratic sensor in favour of a healthy one, confirm the healthy sensor's data is genuinely representative and monitor the erratic one — automatic resilience handling one failed input doesn't remove the DPO's job of understanding what's happening.

4. Consequence / Reassess / Escalate

Automated resilience buys time and stability but doesn't answer why the sensor failed, whether it might recur, or what a second failure in that same input type would mean with no remaining redundancy left in it.

5. Recover / Verify / Human factor

Once a fault is confirmed hardware and scheduled for replacement, recognise the vessel is effectively down to a single reliable sensor of that type until fixed — not fully resolved just because the immediate symptom is handled. Trap: treating automated correction as equivalent to the underlying problem being solved.

Sources: IMO MSC.1/Circ.1580 (sensor requirements), IMCA M252. This guide is educational content, not a substitute for accredited DP training, vessel-specific FMEA/ASOG, or full-mission simulator assessment. Crew Connect never infers compliance with a specific vessel's applicable requirements — always verify against your own approved documents.