A yacht was seen from the 37,500-ton Pride of Bilbao ferry
Three yachtsmen may have survived had a P&O car ferry officer not "ignored evidence" his ship may have sunk or swamped their boat, a court heard.
Michael Hubble has denied manslaughter through gross negligence and engaging in conduct likely to cause death or serious injury to the three men.
The sailors, from London and Kent, were found dead in the English Channel in August after their yacht vanished.
Mr Hubble, 62, from Folkestone, Kent, is appearing at Winchester Crown Court.
The court heard officer-of-the-watch Mr Hubble "chose to ignore" the fact the 37,500-ton Pride of Bilbao ferry had come very close to the men's 25ft (7.6m) yacht Ouzo off the Isle of Wight and he did nothing to raise the alarm.
Jurors were told his lack of action led to the deaths of school and university friends James Meaby and Rupert Saunders, both 36 and from Tooting, south London and Jason Downer, 35, from Kent, because it was alleged they would have survived if Mr Hubble had called the captain.
Christopher Parker QC, prosecuting, said the 24-year-old sailfish sloop Ouzo disappeared without a trace and experienced sailor Mr Meaby had survived for at least 12 hours in the water before he died from hypothermia and drowning.
Mr Parker alleged the "well maintained and equipped" yacht was either overwhelmed by the 580ft (177m) ferry's wave as she passed or she collided with her.
"The defendant said he saw a light at the stern. He concluded the yacht had come to no harm," he said.
Left to right - Jason Downer, Rupert Saunders and James Meaby all died
"He carried on to Bilbao. Importantly, we say, he took no action to ascertain that the crew of the yacht was safe as a result of that collision or very near miss.
"If Michael Hubble had done what we say he should have done there would have been a rescue operation and these three men would have survived."
Experienced sailors Mr Saunders - the owner and skipper of the Ouzo - and Mr Downer survived for at least three hours before they died from either hypothermia and/or drowning.
All three men were found dead with their lifejackets on and inflated and Mr Parker said Mr Saunders insisted they were worn at all times.
Mr Hubble, of Wine House Lane, Capel-le-Ferne - who had 40 years' experience - was on the ferry's bridge with the lookout David Smith when it left Portsmouth en route for northern Spain, the court heard.
Mr Parker said the Ouzo did not show up on the ferry's radar, adding Mr Smith saw the lights of a vessel very close off the starboard bow at 0107 GMT on 21 August, according to the ship's voyage data recorder.
He said the captain had gone to bed at 1230 BST and the ship was travelling at 21 knots with Mr Hubble now in charge.
The lookout, Mr Smith, had taken over at 0100 BST when he spotted something in front of the ferry and became alarmed.
Mr Parker said: "He realised he was looking at the lights of a smaller vessel and it appeared to be crossing right to left across the bows of the ferry.
"He shouted a warning twice. David Smith saw an average-sized yacht go down the starboard side of the ship."
The lookout ran across the bridge because "it was that much of an emergency", Mr Parker said, and lost sight of the yacht. He kept looking and eventually saw a red light.
At this point Mr Hubble was also checking and walked across to the port side of the bridge where he told police during interview he saw a white light off the port stern which had led him to be satisfied there was no problem.
Mr Hubble made a manoeuvre, first to port, and then back to starboard to avoid the yacht, Mr Parker added.
He told the court that on the way back from Spain on 22 August, there was a radio message to the Pride of Bilbao informing ships of the discovery of Mr Meaby's body 10 miles south of Nab Tower off the Isle of Wight, but Mr Hubble "failed to tell anybody what had happened".
The Ouzo left Bembridge on the Isle of Wight on 20 August to sail to Devon for the Dartmouth Regatta, but it never arrived.
The trial continues.