|The overturned hull of the Cheeki Rafiki, some 700 miles off eastern Canada|
Douglas Innes, boss of the yachting firm, and his company Stormforce Coaching were convicted at Winchester Crown Court.
However, the jury failed to reach verdicts on four manslaughter charges relating to the deaths of skipper Andrew Bridge, 22, from Farnham; James Male, 22, from Southampton; and Steve Warren, 52, and Paul Goslin, 56, both from Somerset.
Nigel Lickley QC, prosecuting, said they would be seeking a retrial on the four charges. Innes was released on unconditional bail until a future hearing on a date to be set.
The court heard there was a fault with bolts holding the keel to the hull
The sailors died when the boat capsized in the middle of the Atlantic, 700 miles from Canada's eastern Nova Scotia province, as the 40ft vessel was returning from Antigua.
Mr Lickey said the yacht had grounded three times before the incident and had an undetected fault with the bolts holding the three-ton keel to the hull.
He said the problem had caused the keel to fall off in bad weather.
Mr Lickey told the court the boat was not properly licensed for the voyage and that Innes picked an "unsafe" route because it was shorter and meant it could get back to the UK in time for other charters.
"The yacht was therefore unsound, broken and unsafe before the four men left Antigua," said Mr Lickey.
"The yacht had been neglected, not maintained and importantly, because the yacht was used commercially by Mr Innes and his company, not inspected as required."
When Innes got an email from the skipper marked "urgent", the jury heard he carried on drinking in a pub before alerting the coastguard.
The company boss told the trial the fault with the keel was hidden and would not necessarily have been spotted in an inspection.
Innes also denied that he had tried to save money by taking the northern route back to Britain.
Following the verdict, Kay Coombes, sister of Mr Warren, spoke outside court on behalf of all the families, saying it had been "a long three years and a long trial".
She said they were "in agreement with the guilty verdict" on the safety charges but could not comment further because of the retrial.
Mr Goslin's widow Cressida said of the trial: "It has brought us much closer together, we are like a family."