Samuel Mackay was appointed Assistant Surgeon to H.M.S. Erebus in 1814. 
He was appointed surgeon to H.M.S. Tweed in 1835. He was appointed surgeon to H.M.S. Winchester 28 March 1839. H.M.S. Winchester was built in 1822, 1407 tons. 288 officers and men, 47 boys and 60 marines served on board. She was Flag Ship to Commander-in-Chief, North America and West Indies. John Parker, Captain. 
Samuel Mackay was employed as Surgeon Superintendent on the convict ship Waverley to Van Diemen's Land in 1842.
On 25th August and 1st September 1842 one hundred and forty seven female convicts and forty of their children were embarked on the Waverley from the depot at Grange Gorman Lane, Dublin, all in a healthy state.
The Waverley departed Dublin 4th September 1842. There was fine weather for most of the voyage to Australia and therefore the prisoners and children were allowed on deck from 9 am to 6pm when they were mustered and returned to the prison for the night.
There were only eleven cases in the surgeon's journal and one death, that of a young boy. Samuel Mackay was careful to keep the Waverley prison clean and well ventilated and the convicts arrived at the Derwent on 15th December 1842 in a healthy state. 
1). National Archives
. Medical journal and copy of sick book of the Waverley, convict ship, from 4 August to 21 December 1842 by Samuel Mackey, Surgeon Superintendent, during which time the said ship was employed in transporting convicts to Hobart Town.
2). Medical Journal of Samuel Mackay on the voyage of the Waverley to VDL. Ancestry.com. UK, Royal Navy Medical Journals, 1817-1857 The National Archives. Kew, Richmond, Surrey.
 Naval Chronicle
 The London Medical and Surgical Journal
 The New Navy List
 Haultain, C. (compiled), The New Navy List, 1840, p. 226