DP Mini Guide: DP System Resilience — Defence in Depth

Crew Connect DP Academy · Mini Guide 23

DP System Resilience — Defence in Depth

Topic: Redundancy & Assurance · Sub-topic: System Resilience  ·  Level: Senior DPO / Master  ·  Read time: 9 min

1. What / Why / How

A DP vessel is protected by multiple independent layers — redundant references, an FMEA-verified power/thruster configuration, and an ASOG that limits operations before things get critical. Defence in depth means no single layer is assumed perfect: the layers exist so one layer's failure doesn't immediately become a loss-of-position event.

2. Recognition / Risk / But

When one layer shows genuine weakness — a reference degrades — while the other two still look comfortably fine individually, that's still significant. Resilience isn't about each layer's current state in isolation; it's about how much combined margin remains if a second layer is also tested. But: avoid treating the remaining layers as carrying more of the burden than before without actively reassessing whether they're genuinely up to that.

3. Now / What next / Decision / Why

Explicitly ask: with one layer degraded, does the remaining redundancy and ASOG margin still provide genuine defence in depth, or has the vessel quietly become reliant on fewer effective layers than the design assumed? If the latter, the threshold for further caution should tighten — even while every individual measure still passes.

4. Consequence / Reassess / Escalate

'Within limits on every individual measure' can still describe a vessel with much less genuine resilience than an hour ago. Defence in depth is about the combined, structural strength of the whole system.

5. Recover / Verify / Human factor

Restoring the specific component that degraded doesn't by itself confirm the whole system is back to its designed state. Trap: assuming full resilience is automatically restored the moment the one obvious fault clears.

Sources: IMO MSC.1/Circ.1580, IMCA M166 Rev.3, IMCA M103 Rev.5.2. 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.