A monohull offshore drilling vessel comprising: - a hull having a moonpool; - a multiple firing line hoist system mounted on the hull at said moonpool, the multiple firing line hoist system comprising: ∘ a mast having a top side and a base connected to the hull of the drilling vessel, wherein the mast has a hollow construction with a first side and an opposed second side, ∘ a first hoisting device supported by the mast and having a load attachment device displaceable along a first firing line, which extends on the outside of and adjacent to the first side of the mast; the first hoisting device being adapted to build and lower a riser string at the first side of the mast; ∘ a second hoisting device supported by the mast and having a load attachment device displaceable along a second firing line, which extends on the outside of and adjacent to the second side of the mast; the second hoisting device being provided with a rotary drilling drive and being adapted to assemble and disassemble a drill string at the second side of the mast and to effect drilling in the associated second firing line; ∘ wherein the first and second hoisting devices each include one or more cables and one or more associated winches to manipulate the position of each of the load attachment devices relative to the mast, wherein the vessel is provided with a suspended riser transfer device, which includes a support frame and a pair of associated rails which extend in longitudinal direction along the moonpool allowing to displace the support frame in longitudinal direction of the moonpool while supporting a riser string of interconnected risers general between a rear moonpool area and a front moonpool area, so as to pass underneath the base of the mast. - a hull having a moonpool; - a multiple firing line hoist system mounted on the hull at said moonpool, the multiple firing line hoist system comprising: ∘ a mast having a top side and a base connected to the hull of the drilling vessel, wherein the mast has a hollow construction with a first side and an opposed second side, ∘ a first hoisting device supported by the mast and having a load attachment device displaceable along a first firing line, which extends on the outside of and adjacent to the first side of the mast; the first hoisting device being adapted to build and lower a riser string at the first side of the mast; ∘ a second hoisting device supported by the mast and having a load attachment device displaceable along a second firing line, which extends on the outside of and adjacent to the second side of the mast; the second hoisting device being provided with a rotary drilling drive and being adapted to assemble and disassemble a drill string at the second side of the mast and to effect drilling in the associated second firing line; ∘ wherein the first and second hoisting devices each include one or more cables and one or more associated winches to manipulate the position of each of the load attachment devices relative to the mast, wherein the vessel is provided with a suspended riser transfer device, which includes a support frame and a pair of associated rails which extend in longitudinal direction along the moonpool allowing to displace the support frame in longitudinal direction of the moonpool while supporting a riser string of interconnected risers general between a rear moonpool area and a front moonpool area, so as to pass underneath the base of the mast. ∘ a mast having a top side and a base connected to the hull of the drilling vessel, wherein the mast has a hollow construction with a first side and an opposed second side, ∘ a first hoisting device supported by the mast and having a load attachment device displaceable along a first firing line, which extends on the outside of and adjacent to the first side of the mast; the first hoisting device being adapted to build and lower a riser string at the first side of the mast; ∘ a second hoisting device supported by the mast and having a load attachment device displaceable along a second firing line, which extends on the outside of and adjacent to the second side of the mast; the second hoisting device being provided with a rotary drilling drive and being adapted to assemble and disassemble a drill string at the second side of the mast and to effect drilling in the associated second firing line; ∘ wherein the first and second hoisting devices each include one or more cables and one or more associated winches to manipulate the position of each of the load attachment devices relative to the mast,