Shared mental models can be hazardous when they are based on inadequate data and don’t match reality, as the chief mate and lookout of the offshore supply vessel Far Swan discovered on the night of 6 October 2010 when it collided with the barge Miclyn 131 being towed by an aluminium catamaran Global Supplier. Confirmation bias does not help, either.
That evening Global Supplier was towing the flat barge Miclyn 131, a total tow of around 180 metres from the bow of Global Supplier to the stern of Miclyn 131. Global Supplier was not showing the requisite two white masthead lights in a vertical line and a yellow towing light in a vertical line above its sternlight. The lights had been ordered but not yet fitted.
Global Supplier was not fitted with AIS or radar and was not required to be.
The barge was equipped with portable BargeSafe lights which should have been visible at three nautical miles. They were placed in such a way that the lights were easily missed against background lights and were all-round rather than sectored, making them more difficult to determine accurately at night.