Uncontrolled release of walk to work gangway

What happened?

A walk-to-work (W2W) gangway system broke loose from its connection point.  The incident occurred during transfer of four persons to an offshore wind installation.  The first person got the green light (operated manually) to transfer across and did so without problems.  After the first person had transferred, the system moved up and down and slipped upwards from its push-on point and came into contact with a floor grating that came loose, resulting in minor damage.  The transfer was aborted, and further transfers were done using a CTV (crew transfer vessel).

Our member’s investigation noted the following:

• The gangway system was tested before the incident and it was observed that the system seemed to be reacting slower than normal, but as it performed well under tests earlier that day it was agreed between operator and captain to start operations;
• There were slight differences in the push-on point design on this installation (a substation) than on the turbine towers (see illustration);
• The weather and sea state at the time was within the working limits for the gangway system (actual 1.5 m and 15 knots versus design 3m Hs & 30 knots wind).

What went wrong?  What were the causes?

Investigation of the software control for the gangway system Active Motion Compensation (AMC) revealed that the performance for boom motion was not optimal.  Corrections were made to the software parameters.

The primary cause was found to be that due to reduced accuracy of the AMC, the vertical force acting on the connection point led to connection failure.

What actions were taken?  What lessons were learned?

Corrective steps to prevent future incidents:

• AMC performance to be verified during annual inspection;
• Before connecting the gangway, position the gangway approximately 1m from connection point, visually verify that AMC is stable and that the control error is within reasonable limits;
• Verify that the connection point is designed to fit the gangway with respect to shape and load.

Members may wish to refer to:

• LTI: Feet trapped in motion compensated telescopic gangway
• Crane motion reference unit (MRU) malfunctions after overheating
• Near-miss during transfer operations from a crew transfer vessel (CTV) to a turbine tower
• Near-miss incidents during personnel transfer to offshore renewable energy installations