Question 1

The saturation system alarm sounds — umbilical tension has increased by 35% above normal. The diving superintendent confirms the vessel has moved relative to the bell. The crane operator can see the crane wire is now at an angle. The bell is at 38m depth with Diver A at 35m on his way up.

With confirmed vessel movement putting the umbilical under load, what is the master's immediate command?

Accepted Answer

Use all available thrust to move the vessel back toward the bell's original position as rapidly as safely possible, using crane wire angle as a visual reference for direction, while the dive team manage the umbilical tension and the diver is told to hold his current depth and stop ascending until vessel position is corrected With the crane wire visibly at an angle, the master has a direction reference — the crane wire points toward the bell. Manual thrust to correct vessel position toward the bell reduces umbilical tension and corrects the geometric problem. Holding the diver at 35m buys time for the position correction without resuming ascent through a taut umbilical geometry. Lowering the bell increases the umbilical catenary but does not address the horizontal displacement. Stopping all thrusters removes the ability to correct position. Cutting the umbilical is a catastrophic, irreversible action that severs the diver's breathing gas supply and should never be considered unless the alternative is worse — which it is not here while position correction remains possible.

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.