9.3 Mode Selection & Practical Setup
Key Takeaways
- Enter DP through a disciplined sequence: checklists, power plant ready, thrusters online, PRS enabled and selected, model building, then Auto DP after setpoints and settling.
- Drop from Auto DP to joystick when automatic hold is unsafe or unsuitable—unstable references, need for direct escape thrust, or procedure/ASOG requires manual combined control.
- Mixed modes (for example auto heading with manual position) are legitimate on many systems for approach and fine manoeuvring; know what is automatic and what you still fly.
- Near platforms and other assets, mode choice is a risk decision: Auto DP for stable hold, joystick for controlled moves/escape feel, IJS only when main DP is unavailable or being tested as backup.
- Exam scenarios reward the safest mode for the phase of the operation—not the mode that sounds most ‘automatic’ or most ‘manual’ by habit.
Mode selection is a procedure, not a single button mash
Induction theory and simulator assessments both punish the candidate who “jumps straight to Auto” without a setup chain—or who freezes in Auto when the situation demands joystick or IJS. This section ties Auto DP, joystick, and IJS into one operational picture: how you enter DP, when you leave Auto, what mixed modes mean, and how exam scenarios near a platform should be answered.
Practical sequence to enter DP (and Auto DP)
Vendor checklists differ, but a defensible common sequence looks like this:
| Step | Action | Why it matters |
|---|---|---|
| 1 | Pre-DP checklist / bridge team brief | Roles, limits, escape route, ASOG status colours, weather |
| 2 | Power plant ready | Adequate generators online, bus configuration per procedure (open/closed tie as planned), spinning reserve |
| 3 | Thrusters online and enabled for DP | No hidden disabled unit; forbidden zones set for the operation |
| 4 | Sensors healthy | Gyros selected/voting, wind, MRU/VRU, UPS status |
| 5 | PRS enable and select | Enough independent references for the class/operation; deselect known bad units |
| 6 | Build / accept the model | Estimate and residuals sensible while manoeuvring or on approach |
| 7 | Set position and heading setpoints | Present position/heading freeze only when estimate is stable |
| 8 | Select Auto DP (or staged auto position/heading) | Closed-loop hold begins |
| 9 | Settle and verify | Footprint, thruster pattern, alarms quiet enough to proceed |
| 10 | Enter operational status | Green/advisory per ASOG only after setup proven |
Skipping PRS selection and model confidence is a classic way to enter Auto DP into a thrashing, alarming mess. Skipping the brief means nobody knows who takes IJS if main DP dies during the first hose connection.
Checklists are memory tools under load
Written DP checklists exist because critical steps are easy to omit when weather, traffic, and client pressure rise. Use them for:
- start of DP operations,
- change of operational mode (e.g. entering 500 m zone),
- after thruster/power/reference changes,
- handover between DPOs,
- restoration after a failure.
Checklists do not replace judgment; they structure it. On exam items, “follow the vessel DP checklist / company procedure” is almost always safer than inventing a random order.
When to drop from Auto DP to joystick
Dropping mode is not failure of the DPO—it is often correct risk management.
| Trigger | Prefer joystick (main system) when… |
|---|---|
| Unstable Auto hold | PRS conflict or noise drives thruster thrash after deselect attempts |
| Deliberate large move | Operator wants direct demand rather than repeated setpoint changes |
| Escape / clear structure | Immediate thrust vector control for a planned exit |
| ASOG / Master direction | Status requires manual control or stop critical auto activity |
| Fine berthing feel | Closing alongside where human rate control is preferred |
When dropping to joystick:
- Announce the mode change to the bridge team
- Confirm auto heading on/off intentionally (do not leave heading floating by accident)
- Watch thruster response and clearances
- Re-enter Auto DP only after references and plant are healthy and setpoints are re-established
Drop to IJS when main DP is failed or you are conducting a planned IJS drill—not as a routine alternative to main joystick when main DP is healthy.
Mixed modes: auto heading + manual position
Many systems allow mixed control, most commonly:
- Auto heading + manual (joystick) position
- Less often, auto position with manual heading (vendor-dependent; know your ship)
| Mixed mode | What the computer holds | What the DPO flies | Typical use |
|---|---|---|---|
| Auto heading + joystick position | Yaw to heading setpoint | Surge/sway demand | Approach on weather heading, slide into box |
| Full Auto DP | Position and heading | Supervision / setpoint changes | Steady work on location |
| Full joystick (manual heading too) | Neither position nor heading auto | All three DOF demand | Quick heading change while translating |
Exam-critical idea: know which loops are closed. If auto heading is on, twisting the stick may not free yaw the way you expect. If only position is manual, a heading fault still needs attention. Mixed mode is powerful for approach; it is also a common source of “I thought heading was manual” errors.
Mode choice near a platform (exam scenarios)
Near a platform, FPSO, or similar asset, mode choice maps to phase of operation:
| Phase near platform | Typical mode choice | Rationale |
|---|---|---|
| Open-water transit to 500 m | Not DP, or standby / setup as required | Not yet station-keeping task |
| 500 m entry / approach | Joystick or mixed auto heading + joystick; careful setup of PRS | Controlled closure, human rate feel |
| On location, critical work | Auto DP with healthy multi-PRS, settled model | Stable hold, consequence analysis meaningful |
| Worsening weather / yellow ASOG | May remain Auto with reduced activity, or prepare joystick escape | Follow ASOG; do not invent hero holds |
| Main DP computer failure | IJS + escape plan | Independent backup path |
| Abort / drive clear | Joystick (or IJS if main dead) with briefed heading | Prioritise clearance over perfect setpoint |
Scenario A — Stable cargo ops. References good, thrusters and power healthy, weather inside limits. Correct: remain in Auto DP, monitor alarms and consequence analysis, do not casually flip to IJS “for fun.”
Scenario B — Wild relative PRS during crane work. Auto thrusters thrash; position alarms. Correct path: deselect bad PRS; if still unstable, joystick control, stop critical deck work, restore references, then re-settle in Auto before resuming.
Scenario C — Dual process-station failure 40 m from legs. Correct: IJS, controlled thrust on escape heading, communications, do not wait for main Auto to “come back” while closing the structure.
Scenario D — Exam distractor. “Always use joystick near platforms because Auto is banned.” False. Auto DP is standard for holding once set up; joystick is for manoeuvring and recovery, not a permanent ban on automatic hold.
Linking modes to thrusters, power, and references
Mode selection never lives alone:
- Thrusters offline shrink what Auto or joystick can achieve; capability after failure may force stop work even if mode is “correct.”
- Power limits can make Auto look like it is failing when TAL is simply saturated.
- Single PRS may allow temporary Auto but violates independence expectations for critical Class 2/3 work—mode cannot invent a second reference.
| If this is true… | Mode alone cannot fix it |
|---|---|
| Worst-case thruster loss leaves insufficient force | Need weather/heading/work status change |
| Bus black on one side | Need power recovery / remaining thruster plan |
| Common-mode GNSS only | Need independent relative PRS before critical hold |
| DPO untrained on IJS | Need training before the failure, not after |
Practical setup habits that score marks
- Brief modes in the pre-job talk: who engages Auto, who takes joystick, who takes IJS
- Stabilise PRS before freezing present position as setpoint
- Enable thrusters honestly — a thruster showing online but not producing force is a silent capability cut
- Settle after every major mode change
- Announce mode changes so Master, ECR, and deck share the same mental model
- Return to Auto when the reason for manual control has cleared and setup is re-validated
Exam traps for mode selection
| Trap | Correction |
|---|---|
| “Enter Auto before thrusters/PRS ready” | Sequence: plant → thrusters → sensors/PRS → model → setpoints → Auto → settle |
| “Never leave Auto once selected” | Drop to joystick/IJS when safety requires it |
| “IJS is normal approach mode” | Main joystick/Auto for normal ops; IJS for independence/failure |
| “Mixed mode means fully hands-off” | Only the selected loops are automatic |
| “Near platform always ban Auto DP” | Auto is correct for stable hold; phase-dependent choice |
Bottom line: build DP in a checklist sequence, use Auto DP for settled station-keeping, drop to joystick when you must command force or Auto is unsuitable, use mixed modes knowingly, and treat IJS as the independent last-resort (and drill) path—especially in platform-proximity exam scenarios where the phase of the job dictates the mode.
Which sequence best reflects a disciplined practical entry into Auto DP?
During stable critical work on location with healthy multi-PRS, thrusters, and power, which mode is normally preferred?
When is dropping from Auto DP to main joystick mode most appropriate?
A DP vessel 40 m from platform legs suffers a complete main DP computer failure. What is the best mode-selection response?