IMCA DP Practitioner common mistakes
IMCA DP Practitioner · Understand the traps and how to avoid them.
Treating DP as a single-sensor autopilot and answering 'the DP keeps position' when asked what happens after one position-reference (PRS) drops out, instead of stating that the DP continues on the remaining references and only degrades when the usable reference set falls below the redundancy required for the current DP class.
Candidates who have only seen DP from a console assume the system 'holds' regardless of inputs, so they skip the concept of a reference set and its voting/consistency checks. The exam tests exactly that chain of reasoning.
What to do instead
Before answering any PRS question, write down: number of PRS available, DP class requirement, and whether the remaining references are independent and diverse. Practise describing degradation step by step (dropout → rejection → alarm → status change) until it is automatic.
Confusing DP equipment classes (Class 1, 2, 3) with the IMO equipment-class definitions and with the operational redundancy concept, for example claiming Class 2 requires two independent DP control systems or that Class 3 needs a fully duplicated power plant on separate switchboards without any single point of failure.
Class definitions are short and similar, so candidates memorise fragments and then over- or under-state the redundancy. The distinction between 'loss of position' consequences and the equipment arrangement is easy to blur under time pressure.
What to do instead
Build a one-page table: class, worst-case single failure to be tolerated, consequence of loss of position, and typical vessel use. Test yourself by explaining why a Class 3 vessel must survive a single failure including fire or flooding in one compartment.
Answering DP capability-plot questions by intuition, e.g. saying the vessel can hold position in a given wind/current/wave combination because 'the thrusters look big enough', rather than reading the worst-case environmental direction and the limiting thruster configuration from the capability plot.
Capability plots are graphical and candidates skip the axes, the environmental direction convention, and the difference between intact and worst-case single-failure plots. They then guess from the shape of the envelope.
What to do instead
Practise reading plots with the axes labelled: environmental direction around the compass, wind speed on the radial axis, and separate curves for intact and failure cases. Always state which curve and which failure case you are using before giving a number.
Describing a DP incident or drill by listing alarms in the order they appeared rather than reconstructing the causal chain (environmental change → reference degradation → operator action → loss of position), and omitting the operator's decision points.
Candidates recall the alarm log because it is memorable, but the exam asks for cause and effect. Without a structured narrative the answer reads as a list and misses the assessed reasoning.
What to do instead
Use a fixed template for incident answers: initiating event, system response, operator perception, operator action, outcome, and the barrier that failed. Rehearse it on two or three generic scenarios until the structure is habitual.
Treating the DP operator's role as passive monitoring and answering that the operator should 'wait for the alarm' or 'let the DP sort it out', instead of describing proactive watchkeeping: checking position, heading, reference status, thruster load, and environmental trends at defined intervals.
Modern DP is highly automated, so candidates underestimate the human barrier. Exam scenarios are often built around an operator who did not notice a slow drift or a reference slowly diverging.
What to do instead
Learn a concrete watchkeeping routine (what to check, how often, what trend triggers action) and quote it when asked about operator responsibilities. Link each check to the failure it would detect.
Mixing up the roles of position references and sensors, for example treating a gyrocompass or a wind sensor as a position reference, or assuming a hydroacoustic position reference (HPR) and a taut wire measure position in the same way and with the same failure modes.
All these devices feed the DP, so candidates group them together. The exam distinguishes position references (which give position) from heading and environmental sensors (which give heading or feed-forward).
What to do instead
Sort every device into: position reference, heading reference, environmental sensor, or thruster feedback. For each position reference, note its principle, its accuracy, and its typical failure mode (acoustic multipath, wire angle, GNSS multipath, radar interference).
Giving a single generic answer to 'what is a DP FMEA and why does it matter' instead of stating that it identifies single points of failure, defines the worst-case failure design intent, and drives the capability plot, the operating procedures, and the annual trials.
The FMEA is a document candidates have heard of but rarely read. They answer with a definition and miss the links to trials, procedures, and class.
What to do instead
Learn the FMEA as a chain: failure modes → effects → worst-case failure → design intent → proving trials → operating limits. Be ready to say which document or test proves each link.
Assuming DP trials and annual surveys are paperwork exercises, and answering that the surveyor 'checks the certificate', rather than describing functional tests such as reference-system comparison, thruster response, and simulated failure of a single component.
Candidates without sea time have not seen trials and default to administrative answers. The exam tests whether you know trials prove the FMEA assumptions in practice.
What to do instead
Memorise a short list of trial items and what each proves: PRS comparison (reference health), thruster step tests (response and saturation), and simulated single failures (redundancy). Tie each item back to the FMEA claim it validates.
Answering DP station-keeping questions without separating the three axes: surge/sway position, heading, and the thruster allocation that achieves them, so the answer ignores that a heading change alters the thruster demand and can push the vessel outside the capability envelope.
Position and heading are displayed together, so candidates treat them as one quantity. The exam probes whether you understand that heading is actively controlled and consumes thrust capacity.
What to do instead
For every station-keeping question, state the target position, the target heading, and the environmental direction, then reason about which thrusters are loaded. Practise explaining why a heading change can be as demanding as a position change.
Using vague language such as 'the DP should be reliable' or 'the operator must be competent' where the question expects a specific limit, alarm, or procedure, and failing to state the numeric or procedural criterion that makes the answer assessable.
Candidates fear giving a wrong number, so they hedge. Marking schemes reward the specific criterion, and hedging reads as not knowing the standard.
What to do instead
For each topic, prepare one concrete anchor: a defined alarm, a class requirement, a trial item, or a documented procedure step. If unsure of a number, give the qualitative criterion explicitly and say what evidence would confirm it.