The five told a Spanish court how they were part of a group of 12 friends who joined 186 others on the Captain Nemo.
The ship had a crew of three including the captain, and about seven staff from the party organisers who had hired the vessel.
It left San Antonio port in Ibiza at 6.35pm and anchored a few miles away where the passengers were allowed to jump off and swim.
At 9pm it began its voyage back to the port.
Shortly afterwards Patrick Bourke decided to jump from 5 metres up on the top deck after being dared, the court was told.
Patrick Bourke was rescued by a passing boat after 90 minutes in the sea, the court heard.
Patrick Bourke told the court: “I thought the boat was going to stop because we were so far out.
“It was travelling very fast and within a few seconds I couldn’t see it.
“It all happened so quickly. When I realised it wasn’t going to stop I took off my sandals and began to swim back.
“I didn’t see anyone throw any lifesavers. The boat made no attempt to stop.” Another friend Garry Henebry, said he pleaded with the captain for help when he realised his friends were overboard.
He said: “I went up to the captain and tried to speak to him in English but he didn’t understand me. So I went up to a Scottish barman and told him there was a man overboard.
“I begged him to stop the boat. I was hysterical because I was trying to save my friend, and he thought I was looking for trouble or trying to fight him. I got down on my hands and knees and begged him to stop the boat.
“The boat slowed down, and that’s when Brazil jumped in. Brazil thought the boat was going to stop. I tried to throw in a lifesaver but they were all tied up, and I couldn’t see any life vests.”
Brazil Bourke’s body was found near the shore the following morning.
Another friend Conor Henebry said he drank no alcohol on the day.
“I was at Brazil’s side and I saw him jump in. He handed his camera to our friend Garry, and said the captain said we could jump in. He thought the boat was going to stop.”
Another friend John Carmody claimed he had tried to untie the lifesavers but had failed.
Defence lawyers insist the lifesavers were not tied up, but Mr Carmody said: “I am 100% clear they were tied together and tied to the boat.”