Apparatus (12) for transferring fluid between floating vessels (10, 11) is described, comprising a submerged rigid transfer arm (13) carrying a fluid pipeline (16). The apparatus (12) is provided with thrusters (21) and positioning monitoring means (24). A control system (25) operates the thrusters (21) to move the arm (13) if the position monitoring means (24) shows the arm (13) and the second vessel (11) is outside a given range, to restore the separation to within the range. The pipeline (16) may be located in a tunnel (30) on the arm (13) which opens above the waterline at each end to allow personnel access therein for inspection and maintenance of the pipeline (16).