I was sorry to learn that David St John Thomas had died. He was the David in the David & Charles [Charles was Charles Hadfield] publishing company, which published Ruth Delany’s The Grand Canal of Ireland, V T H & D R Delany’s The Canals of the South of Ireland, Patrick Flanagan’s The Ballinamore and Ballyconnell Canal, D B McNeill’s Irish Passenger Steamship Services (two volumes: north and south), P J G Ransom’s Holiday Cruising in Ireland: a guide to Irish inland waterways and W A McCutcheon’s The Canals of the North of Ireland.
That lot laid the foundations for the study of the history of Irish waterways, but Irish waterways were just one small part of a massive list.
There are obituaries online including one in The Scotsman and another in the The Daily Telegraph.
Irish waterways history 
Very sad. I owe a debt of gratitude to David & Charles. Their books are prominent on my shelves. We are very fortunate that they were willing to publish works on often obscure subjects, which could never be big sellers.
I must credit David & Charles with introducing me to industrial archaeology in the 1960s. I grew up in a grimy industrial town, and regarded archaeology as being all to do with ancient ruins in nice places. I chanced upon one of D&C’s then-new regionalindustrial archaeology books, and was amazed when the first photo I saw showed a row of apparently nondescript terraced houses, located right across the street from where I lived. Turns out they had been textile workshops. I was hooked from then on.
Thank you, Mr David Thomas, and Mr Charles Hadfield.