Bill, you're almost right. It was written by Peggy Seeger. The following are an item from the Weekly Scotsman reporting the disaster and some album notes:

[1959?60?:] The lifeboat Mona, which over the years had saved more than 100 lives, was lost answering a distress call from the North Carr lightship. She left Broughty Ferry at 3.13 a.m. in a full gale. It is known she passed the dangerous bar of the Tay, but after that nothing further is known as to how her crew lost their lives, although it is certain she must have capsized. It was early the next day that a helicopter from R.A.F. Leuchars spotted the Mona stranded on the sands near Buddon Ness. At about the same time Senior Coastguard Officer David Mearns of Carnoustie heard of the lifeboat and alerted the life-saving team of Carnoustie. Said Officer Mearns: "One of the coastguard officers came in and said the lifeboat was on the sands. We all went down, but there was nothing we could do. The body of one man was lying on the sand a little way from the boat ... the sea rushing over him. There were four men in the wheelhouse and one in the engine room. The boat was flooded. Later we found the body of another man half a mile away across the sands." (Weekly Scotsman ??.Dec/Jan?.)

[1975:] This song tells the tale of a sea disaster in December 1959, when Britain's north sea coast was lashed by giant winds. The Broughty Ferry lifeboat Mona capsized losing all eight men while trying to rescue the crew of the Broughty lightship. (Jim McCann, notes 'Dubliners Now')