9.2 Joystick & Independent Joystick System

Two different “joysticks” — do not mix them up

On DP vessels the word joystick appears in two related but exam-critical ideas:

1. DP Joystick mode (manual position / combined thruster demand through the main DP system)
2. Independent Joystick System (IJS) — a separate backup thruster control path if the main DP fails

Both let a human command combined thruster force. Only the second is specifically engineered as an independent recovery path when the automatic DP computers or main DP control chain are lost. Mixing them up loses marks on Induction MCQs and causes dangerous hesitation on the simulator.

DP Joystick mode (main system)

In joystick mode, the DPO commands vessel translation (surge and sway demand) with a stick or equivalent HMI. The main DP system’s thrust allocation still converts that demand into individual thruster commands. Heading may be:

• commanded manually (twist grip, heading dial, or stick axis, depending on design), or
• held by auto heading while position remains manual on the stick.

Joystick mode is not the same as walking to each thruster lever. Combined control is the point: one human input, many thrusters coordinated. It is also not Auto DP: if you release the stick (depending on spring-to-zero design), you are not necessarily commanding “hold this earth-fixed position” the way Auto DP does with setpoints.

When joystick mode is preferred

Joystick is a tool, not a punishment mode. Good DPOs choose it deliberately, brief the bridge team, and return to Auto DP when automatic hold is again the right risk posture.

Independent Joystick System (IJS) — the backup path

The Independent Joystick System provides manual combined thruster control that does not rely on the main DP process stations functioning. Design intent:

• If main DP computers crash, freeze, lose both process stations, or otherwise fail as a common mode, the vessel must not be left with no coordinated thruster command.
• IJS commands thrusters through a separate control path, with separate power supply arrangements as required by the vessel’s DP design and class notation.
• IJS typically offers manual position/force demand and often manual or auto heading options similar in feel to the main joystick, but it is not a more powerful automatic DP mode.

[!IMPORTANT] Exam trap: “IJS is a better Auto DP.” Wrong. IJS is backup manual (often with auto heading). It does not replace healthy multi-reference automatic station-keeping and is not a second Kalman filter with superior capability.

Separate power and control — why independence matters

Independence is the whole point. If IJS power and control were fed only through the same failed main DP cabinets, the “backup” would die with the primary. Class and FMEA thinking expect:

• IJS electronics powered from an independent source path (often UPS/emergency arrangements distinct from the failed main DP supply)
• Command routes to thrusters that remain available after the design main-DP failure
• Clear bridge procedures for transferring to IJS (takeover buttons, thruster enable, communication with ECR)

You are not required to recite a particular maker’s wiring diagram. You are required to state that IJS is separate so main DP failure does not remove all combined thruster control.

Regulatory and redundancy role (Class 2 / Class 3)

IMO equipment class philosophy (MSC.1/Circ.1580 for modern vessels; legacy MSC/Circ.645 context still appears in older fleets) requires that Class 2 and Class 3 vessels maintain position-keeping capability after a worst-case single failure. Main DP control system redundancy (dual process stations, etc.) addresses many computer faults. The IJS addresses the residual operational need: a simple, independent means to control thrusters when automatic DP is unavailable.

IJS does not by itself make a vessel Class 3. It is one element in the control and recovery picture alongside power partitions, thruster redundancy, and dual DP computers.

Training to use IJS under stress

Human factors kill recovery time. Under a real main-DP failure near a platform, adrenaline and alarm noise shrink working memory. If the DPO has never drilled:

• where the IJS panel is,
• how to take command from main DP,
• which thrusters remain available,
• how auto heading on IJS is engaged,
• who communicates with the engine room and deck,

…then the first seconds are wasted searching for buttons while the vessel drifts or drives.

Training expectations for NI-minded operators:

1. Know the location and takeover sequence before critical activity starts
2. Practise IJS in harbour drills or simulator (Phase C scenarios often include main DP loss)
3. Brief the bridge team on who drives IJS and who handles communications
4. Prefer a simple escape heading and thrust plan over clever fine positioning when the goal is clear the 500 m zone
5. Return to main DP only when the system is restored, checked, and settled—not mid-crisis experimentation

Worked scenarios

Scenario 1 — Normal approach. DPO uses main joystick mode with auto heading to close distance, then freezes setpoints and selects Auto DP for cargo ops. IJS remains ready but unused.

Scenario 2 — Main DP process station dual failure. Both main DP computers fail. DPO announces failure, takes IJS, applies controlled thrust away from the platform on a pre-briefed escape heading, coordinates with Master/ECR. Auto DP is gone; IJS saves the manoeuvre.

Scenario 3 — Confusion trap. Cadet tries to “select IJS for better Auto DP hold” during normal ops. Wrong tool: stay on main Auto DP when the system is healthy; IJS is not a superior automatic mode.

Exam traps

Bottom line: Joystick mode is manual combined thruster demand on the main DP system (auto heading optional). IJS is the independent backup stick with separate power/control for main-DP failure, central to Class 2/3 recovery thinking, and must be drilled under stress before you need it for real.