Question 1

When a person is being man-ridden from a crane while the vessel is in DP, what additional procedures apply beyond a standard crane lift?

Accepted Answer

Man-riding requires a dedicated man-riding permit, ASOG limits reviewed and likely tightened for position tolerance, a dedicated DP watchkeeper (not distracted by other tasks), the crane operator must have direct communication with the DPO, and the operation must be immediately suspended if any DP alarm sounds or position deviation reaches the amber limit Man-riding from a crane creates a scenario where a DP excursion directly endangers a person in a very vulnerable position — swinging on a crane hook outside the vessel. The DPO's tolerance for excursion must be reduced compared to a standard cargo lift, and the crane operator-DPO communication is the critical link that allows the suspended person to be landed safely before a developing DP situation becomes critical.

Question 2

How does a heavy crane lift affect the DP system's position-keeping model and why does this matter?

Accepted Answer

Lifting a heavy load shifts the vessel's centre of gravity upward and athwartships (depending on crane position), altering the vessel's roll and pitch characteristics and therefore the environmental force response — a DP system not updated with the correct crane position and load may miscalculate the forces needed to maintain position, reducing accuracy Modern DP systems allow the DPO to input crane position and estimated load so the DP model can compensate for the changed stability and force balance. On vessels without automatic crane/load input, the DPO should manually update the model. A heavy load on an extended jib creates significant moment that the DP system must account for to maintain heading and position accurately.

Question 3

What is load pendulation and why does it create a risk for DP position-keeping?

Accepted Answer

Load pendulation is the swinging of a suspended load in an arc below the crane hook, which creates a dynamic, oscillating side force transmitted through the crane structure to the vessel hull — the DP system must counter this cyclic force, and the constant changing direction of the force can cause oscillating thruster demands that stress both the DP system and the power management system A pendulating load creates a lateral force that swings across the beam of the vessel, requiring the DP system to provide corrective thrust in alternating directions. This cyclical demand can cause undesirable roll motions that further increase pendulation (amplifying the problem), and on vessels with limited power, can contribute to demand spikes that stress the PMS or trip generators.