DP Mini Guide: DP Class Notation — Equipment Class & Redundancy

Crew Connect DP Academy · Mini Guide 11

DP Class Notation — Equipment Class & Redundancy

Topic: DP Fundamentals · Sub-topic: Equipment Class  ·  Level: DPO  ·  Read time: 8 min

1. What / Why / How

Equipment Class defines the level of redundancy a DP vessel is designed to have, and specifically what failure it's expected to survive without losing position. Class 1 has no redundancy requirement. Class 2 must survive a single fault in any active system. Class 3 must additionally survive fire or flood in any one compartment. This isn't a certificate formality — it directly shapes what operations the vessel can safely undertake.

2. Recognition / Risk / But

A single-point failure on a DP2 vessel with healthy remaining redundancy is exactly what the notation is designed to survive — that's not automatically cause for alarm. But: the notation describes a design, not a guarantee that applies regardless of the vessel's actual current configuration.

3. Now / What next / Decision / Why

Check whether the current configuration — bus arrangement, which references/thrusters are actually selected, any equipment already unavailable — still matches what the FMEA assumed for that class notation. If it does, that justifies confidence a single further fault shouldn't cause loss of position; it does not remove the need to keep monitoring and reassessing.

4. Consequence / Reassess / Escalate

A higher notation doesn't mean caution can be relaxed for an operation whose own requirements (ASOG, activity risk) set a different bar. And an unmodelled fault — one the FMEA never anticipated — means the vessel may no longer sit within its designed assumptions at all, calling for the same fresh assessment as any other developing situation.

5. Recover / Verify / Human factor

A DPO who only knows the class number, not what it actually covers, can't correctly judge whether a real developing fault is within or beyond what the vessel is designed to handle. Trap: treating the notation as a fixed guarantee that removes the need for ongoing assessment once achieved.

Sources: IMO MSC.1/Circ.1580 (equipment class definitions), 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.