A maritime expert said “human factors” play a major role in most collisions similar to the North Sea crash between a cargo ship and a tanker.
Dr Seyedvahid Vakili, of the University of Southampton, said at this stage it was “difficult to determine the main cause of the collision”.
He said: “In most cases human factors play a significant role.
“This is particularly relevant for container vessels where high workloads and fatigue can be major contributing factors.
“At this stage it needs further comprehensive investigation.”
Charles Clover, founder of marine conservation organisation Blue Marine Foundation, said ship tracking data indicates there were no interruptions in the automatic identification system (AIS) for the vessels, which transmits their location.
He told the PA news agency there were “no apparent AIS gaps for either vessel”.
Tiago Alves, a professor at Cardiff University’s School of Earth and Environmental Sciences, said on Monday that the rescued seafarers “can contribute to a future investigation”.
He said: “The oil tanker was seemingly under a military mission and might have been found, unexpectedly, anchored in an area that is not common for ships to moor.
“The tanker is now visible on vesselfinder.com (a ship tracking website), but it may have also been radar silent at the time of the crash, for security reasons.
“Only a thorough investigation will reach a final conclusion on what happened.”
A spokesperson for the Marine Accident Investigation Branch (MAIB), which works with the Department for Transport, said it deployed a team of investigators to Grimsby on Monday.
She said that it was “yet to be decided” which country will lead the investigation.
Responsibility generally lies with the flag administrations, which in this case is Portugal (for Solong) and the US (for Stena Immaculate).
The UK is liaising with both as it has an interest because the crash happened in its waters.
