A vessel adapted to perform subsea wellbore related operations involving a riser string that is assembled from releasably interconnected riser sections and extends between a subsea wellbore and the vessel. The riser string vertical handling system of the vessel includes a controlled motion device that is adapted to displace the riser string lifting tool in at least one horizontal direction relative to the riser spider device at least whilst travelling between the elevated and lowered position thereof loaded by the riser string suspended from the riser string lifting tool, thereby allowing to establish an inclined travel path with selectively variable inclination of the riser string lifting tool relative to an imaginary vertical line through the riser string passage of the riser spider device, e.g. said inclined travel path having an inclination selected to correspond to an actual water current induced inclination of an upper portion of the riser string during the riser string assembly process.