Detectives investigating the deaths of three sailors and the disappearance of their yacht have said the inquiry will take several weeks to complete.
Left to right, Jason Downer, Rupert Saunders and James Meaby all died
Police are trying to trace all ships and ferries that were in the area south east of the Isle of Wight when the yacht Ouzo went missing last week.
They are currently examining forensic evidence from the hull of Channel ferry Pride of Bilbao.
Ouzo left Bembridge, Isle of Wight, for Dartmouth, Devon, on 20 August.
The bodies of Jason Downer, 35, of Broadstairs, Kent, Rupert Saunders, 36, and James Meaby, 36, both of Tooting, London, were found in the sea off the south east coast of the Isle of Wight two days later.
Post mortem examinations showed that Mr Downer and Mr Saunders died from drowning while Mr Meaby died from a combination of hypothermia and drowning.
No Mayday distress call had been received and the only remnant of their yacht that has been found is a fender.
Coastguards have said the 27ft (8.2m) Sailfish sloop may have been in collision with a larger vessel.
Officers boarded the cross-channel ferry, Pride of Bilbao, in Portsmouth on Tuesday night and used an inflatable boat to examine her after passengers had left the ship.
Marine Accident Investigators have also been studying the vessel's black box recordings, which could contain information on the ferry's position and course from the night the yacht went missing.
Det Insp Nigel Niven said: "This is an on-going inquiry which will take weeks, rather than days.
"We need to identify all heavy commercial traffic in that area of the English Channel south east of the Isle of Wight between 10pm Sunday, August 20, and 8am Monday, August 21.
"We also are seeking information regarding the movements of Ouzo after it left Bembridge at 7.30pm Sunday, August 20.
"The investigation will be long-term and meticulous, and police are liaising closely with the Maritime and Coastguard Agency."