Seán Mhartain was a son to the Buck. There is a dangerous sound between the top of Horse Island and the Black Rock. This is called Súnda Sheáin Mhártain.
Sean was steering a boat home one morning after a night’s fishing. Another boat came up with them and challenged them for a race to the shore. Seán’s boat was being beaten when he “ran the Sound” and so got the lead and won the race. Nobody before or since ever went through this sound which bears Seán’s name.