The pair put out a 999 call to coastguards after running into difficulties in rough seas off Foreland Point, near Lynmouth.
They had left Cardiff early on Tuesday morning bound for Ilfracombe, but their progress was halted off the North Devon coast.
Minehead’s Atlantic 85 lifeboat was launched to locate them after coastguards were unable to establish contact after the initial emergency call.
Richard Gay, a member of the volunteer RNLI crew, said the yacht was found under power but unable to make any headway.
“They had been trying to run against the tide but there appeared to be something wrong with the engine and they simply didn’t have enough power,” he said.
“Basically, they had remained in the same position for four hours. They were both pretty exhausted – they had been at sea since early morning – and one of them was quite badly seasick so our only option was to take them in tow.”
Because of wind and tidal conditions, it took three hours to tow the yacht back to a safe anchorage at Minehead.
Minehead lifeboat station local operations manager Dr John Higgie said the incident had illustrated the need to be aware of tidal conditions in the Bristol Channel.
“It might look just like any body of water – but it’s not,” he said.
“It needs to be treated with a great deal of respect – and that includes ensuring your boat is fit to deal with the speed of the currents, particularly at locations such as Foreland Point.”