Question 1

The vessel has been manually manoeuvred back to a position where crane wire angle is normal and umbilical tension has reduced to near-normal. The diver is at 35m holding depth. The bell is at 38m. The master has one DGNSS unit available and manual joystick control.

Before resuming the diver's ascent, what must be confirmed?

Accepted Answer

That: (1) the vessel's position relative to the bell is verified as stable using crane wire angle, (2) umbilical tension is within normal limits, (3) Diver A is uninjured and not showing signs of stress injury from the tension event, (4) the master is confident the one remaining DGNSS reference is adequate to maintain position for the remaining ascent, and (5) the dive team is ready to manage a further tension event if position moves again Before the diver resumes ascent, the situation must be verified across all dimensions — not just the mechanical ones. Point (3) matters because the sudden tension increase may have subjected the diver to a mechanical jerk via the umbilical. Points (4) and (5) matter because the ascent must now be completed with degraded reference capability, and the team must have a plan if the position moves again. Option D is partially right (every minute at depth does increase decompression risk) but it cannot be used to rush the verification checklist — a second umbilical tension event during a resumed ascent with no plan would be worse than a controlled delay.

Question 2

EMERGENCY SCENARIO — DP2 DIVING SUPPORT VESSEL

Vessel: DP2 DSV, saturation diving system. Location: Subsea pipeline repair, North Sea. Diver A at 92m depth, on umbilical, working on a valve assembly. Diver B on standby in bell at 92m. Bell is deployed on umbilical from crane. References: DGNSS x2, USBL (acoustic, tracking bell transponder). Sea state: 1.2m, wind 14 knots NW. Three gyros all active and agreeing. Position very stable. DPO on watch.

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The USBL unit tracking the bell transponder suddenly drops out — no position data from the acoustic reference. Only DGNSS x2 remain. The USBL display shows 'No Fix.' Diver A is still working on the valve and the dive supervisor is monitoring via CCTV. Position is still showing as stable on the two DGNSS units.

What must the DPO do immediately?

Accepted Answer

Immediately inform the dive supervisor of the USBL dropout, place the operation on heightened alert, investigate the cause of the USBL dropout, and assess whether operations can continue on two DGNSS references alone per the ASOG — the dive supervisor must be told because they may need to decide whether to hold or recover Diver A based on the degraded reference status With a diver at 92m on umbilical, every reference system degradation is simultaneously a diver safety event. The USBL is not merely a DP reference — it is also the primary means of tracking the bell position relative to the vessel. Its dropout immediately changes the information picture for the dive supervisor, who must know. Attempting to restart USBL while Diver A continues working on the bottom defers a safety communication that the dive supervisor needs to make an informed decision. Reducing alert radius does not compensate for a lost reference — it just means smaller excursions trigger the alarm. The ASOG will specify minimum references for diving operations; dropping below that minimum requires immediate ASOG status reassessment.

Question 3

USBL has not recovered. Now, five minutes after the USBL dropout, DGNSS Unit 1 and DGNSS Unit 2 begin to diverge — Unit 1 shows the vessel's position 3.1m south of Unit 2 and the gap is slowly increasing. The dive supervisor has been informed of the USBL dropout and Diver A has been told to hold position at the valve.

With the USBL down and DGNSS units now diverging, what is the DPO's assessment?

Accepted Answer

With USBL already lost, the two DGNSS units diverging are the only remaining references — and a divergence of 3.1m that is increasing means the DPO cannot verify which unit is providing the correct position. This is now a critical reference degradation with a diver at 92m. The dive supervisor must be immediately updated and told the vessel now has no way to verify its true position. Consideration must be given to initiating Diver A's ascent while position is still believed to be acceptable The cascade is developing: first USBL (the acoustic bell-tracking reference) drops out, now the two remaining position references are disagreeing. At this point, the vessel has no verified position. This is the worst possible moment for reference degradation — 92m diver on umbilical, bell deployed, the vessel cannot confirm it is still directly over the work site. The 3.1m divergence is not "within GPS accuracy" in the context of a diver on umbilical — the combined uncertainty of two disagreeing DGNSS units, at 92m depth with an umbilical catenary, means the effective positional uncertainty for the diver is significantly larger. Beginning a controlled diver ascent now, while position is still believed stable, is categorically safer than waiting until position is confirmed to have moved.