Alexander McKechnie was born in Scotland c. 1803. He was appointed Surgeon in the Royal Navy in 1830.
He was appointed Surgeon to the Madagascar in North America and West Indies on 7 June 1836. The Madagascar was ordered home in 1838.
Alexander McKechnie was employed as Surgeon Superintendent on two convict ship voyages to Australia:
Mandarin to Van Diemen's Land in 1840. He kept a Medical Journal from 8 February to 6 July 1840.
Layton to Van Diemen's Land in 1841. Medical Journal from 22 March 1841 to 6 September 1841
Appointed to H.M.S Belleisle
In 1857 as Inspector of Hospitals he was appointed to 'Belleisle' which was a hospital ship used in the Crimean War c. 1854. Staff surgeons J. Jenkins M.D. (1854) and A. Armstrong (acting) were also appointed to the 'Belleisle'. 
Interior of sickbay, HMS Belleisle, Crimean War. Credit: Wellcome Library, London.V0015417 Crimean War: interior of the Belleisle Hospital ship in Faro Credit: Wellcome Library, London.
Alexander McKechnie Alverstoke : Royal Naval Hospital at Haslar
Alexander McKechnie 48, Glasgow University, Doctor of Medicine, Surgeon RN - attached to Haslar Hospital
Mary McKechnie 39
Alexander G McKechnie 7
William B McKechnie 3
Peter G W McKechnie 1
Alexander McKechnie 58, Inspector General of Hospitals
Mary E McKechnie 49
Peter G W McKechnie 11
Mary J McKechnie 9
Medical Register 1865
He was listed in the Medical Register 1865.
Residence 3 Queen's Place, Southsea, Hants
Inspector General of Hospitals and Fleets.
Qualifications - Lic. Fac. Phys. Surg. Glasgow 1821.
M.D. University Glasg. 1829.
Mem Royal College Phys. London 1860.
Alexander McKechnie died on 12 July 1866 at Renfew House, Southsea, Co. Southampton. Widow Mary Elizabeth McKechnie, sole Executrix. Ancestry.com. England and Wales, National Probate Calendar 
3). Marriage of John H. Martin M.D. of Portsmouth to Mary Jane, only daughter of the late Alexander McKechnie M.D., Inspector General of Fleets and Hopsitals at Norbiton, Kingston-on-Thames, on June 6th British Medical Journal 11 July 1868