Hi Ed, If you also obtain
BT 165/990 from the National Archives in Kew which contain official logbooks for various vessels including ST PETERSBURG for the time period you want. The master at the time would have signed the logbook so either way you should have an answer.
Ship's name St. Petersburg Official Number 123940 Date of Voyages 5 July 1914 - 12 November 1914 and 2 January 1914 - 30 June 1914.
Regards
Hugh