SS Mona's Isle was a steam turbine passenger ship that was built in Scotland in 1905 as Onward, renamed Mona's Isle in 1920, and scrapped in Wales in 1948. She was designed as an English Channel ferry for the South Eastern and Chatham Railway (SE&CR), who operated her between Folkestone and Boulogne. In 1920 the Isle of Man Steam Packet Company (IoMSP) bought her and renamed her Mona's Isle. The IoMSP ran her mainly on summer services linking Douglas with Dublin and Belfast. She was the fourth IoMSP ship to be called Mona's Isle.