The steel screw steamer Rio Dorado was built in Northumberland by the Blyth Ship Building & Dry Dock Company in 1924. Registered in London at 4,507 tons gross (2,766 net), she measured 390 feet in length with a 55½ foot beam, and was powered by triple-expansion engines from the North Eastern Engineering Company's works at Newcastle -upon-Tyne.
Of broadly conventional design, she neverless had one highly distinctive feature in that she had an unusual corrugated hull. First used in the freighter Monitoria of 1909, the two longitudinal troughs along the ship's sides apparently improved the flow of water to the propellor - and thus the propulsive efficiency - as well as having a beneficial effect on the steering. Additionally, the lighter scantlings resulting from the design allowed for some extra cargo capacity, as much as 2-300 tons, making it an even greater attraction for shipowners. On the face of it therefore, the corrugated hull was a significant advance in shipbuilding technique but its several advantages were cancelled out, at a stroke, by the huge cost of repairs in the event of accident. Heavy seas and careless docking meant that the occassional replacement of plates was an occupational hazard for every commercial shipping organisation and one which provided a lucrative livlihood for many yards across the world. Even when plates needed to be replaced frequently however, it was a simple and relatively cheap operation when compared to repairing damage to the corrugations on one of these novel hulls. In fact, the cost of even the most basic repairs proved uneconomic and the concept never really caught on. The Newcastle-based Thompson Steamship Company was arguably the most ardent supporter of the corrugated hulled ship and ordered several for their fleet between 1921 and 1928. In total, between 25 and 30 were built over a twenty year period and the last of them survived into the 1960's despite their long-term maintenance problems.
Rio Dorado herself was not so lucky and was lost, presumed sunk by enemy action, during the Second World War. Clearing the Tyne on 27th February 1941 and bound for Baltimore with a cargo of coke, she made a brief call at Oban on 6th March after which she was not heard from again. Thompson's, who had owned her throughout her life, were advised of her presumed loss by the Admiralty on 4th April which indicated the date of sinking as 16th March. It seems possible there were reports of a German raider on her course that day although this information was not released in the interests of wartime secrecy; whatever the case, all thirty-nine of the men aboard Rio Dorado lost their lives and an extremely interesting hybrid steamship became yet another statistic in the causualties of war.