#Position Reference Systems (#PRS) on #DP2 Offshore Vessels

✅ Position Reference Systems (PRS) on DP2 Offshore Vessels For Dynamic Positioning Operators (DPOs), Engineers, and Marine Officers ⸻ 🔹 1. What is a PRS (Position Reference System)? A Position Reference System (PRS) is a critical component of a DP (Dynamic Positioning) system that provides real-time positional data to allow the DP computer to maintain the vessel’s exact position and heading. On a DP2 vessel, redundancy is essential, so multiple independent PRS are required. ⸻ 🔹 2. Purpose of PRS in DP Operations • Detect drift or deviation from set position. • Provide real-time position feedback to DP control system. • Enable vessel to stay in position during: • Cargo operations • Hose connections • Diving support • ROV operations • Platform supply ⸻ 🔹 3. Common Types of PRS on Offshore DP2 Vessels PRS Type Technology Description Use Case DGPS (Differential GPS) Satellite-based Provides corrected GPS data for accurate positioning General DP operations RTK GPS (Real-Time Kinematic) Satellite + Base station High-precision GPS with accuracy of cm-level Close proximity ops Fanbeam / CyScan Laser-based Measures distance and angle to fixed reflector targets Preferred near rigs or platforms RADius Microwave-based Short-range, non-contact radar system Harsh weather or low visibility Hydroacoustic (HPR/USBL) Acoustic Underwater positioning using transponders Subsea ops or poor surface visibility Taut Wire Mechanical Wire from vessel to seabed or fixed structure, measures angle and tension Redundancy, older systems ARTEMIS Microwave Used at longer ranges, often phased out Legacy systems ⸻ 🔹 4. PRS in DP2 System Design (Redundancy and Independence) In DP2, the fail-safe design demands: • Minimum 3 independent PRS feeding data to DP system. • Each PRS must be on separate power and communication lines. • DP system uses voting logic to discard erroneous PRS data. • Loss of one PRS should not compromise station-keeping. ⸻ 🔹 5. DPO Responsibilities with PRS • Verify PRS calibration before operations. • Check line-of-sight for laser systems. • Continuously monitor PRS health via DP alerts/warnings. • Cross-check PRS inputs for consistency. • Initiate manual intervention if one PRS gives erroneous data. • Conduct DP footprint trials if required. • Record PRS performance in DP logbook. ⸻ 🔹 6. PRS Failure Scenario Example (Case-Based) Scenario: During cargo ops at FPSO, Fanbeam target is blocked by crane boom. PRS data becomes erratic. OOW/DPO Actions: • Monitor DP alert: “Fanbeam Input Lost / Quality Degraded”. • Switch to alternate PRS (RTK GPS or RADius). • Inform bridge and Master. • Reposition vessel or request crane movement. • Record incident and recovery action in DP log. ⸻ 🔹 7. PRS Best Practices for Offshore Safety ✅ Maintain clean optics and alignment for laser-based PRS ✅ Ensure back-up PRS are powered and tested ✅ Use real-time graphical tools to monitor PRS health ✅ Maintain updated PRS location reference lists ✅ Log and report any PRS inconsistencies