System for displacing a blowout prevention safety valve for a watercraft provided with an oil drilling tower, said system comprising: - a support structure, intended to be installed on said watercraft and comprising at least one resting platform and at least one suspension platform placed at the top part spaced with respect to said resting platform; - lifting means mechanically mounted on said resting platform to support said safety valve, and movable between at least one lowered position, in which said lifting means support said safety valve in proximity to said resting platform, and a raised position, in which said lifting means support said safety valve in proximity to said suspension platform; - at least one rail mechanically associated with the suspension platform of said support structure and extending along a transfer path intended to connect a parking area to a drilling area susceptible of being associated with the drilling tower of said watercraft; - at least one overhead crane slidably mounted on said at least one rail along said transfer path, and comprising at least one lifting winch susceptible of supporting said safety valve in said parking area above said lifting means; - at least one crane provided with connection means, mounted at said drilling area and susceptible of supporting said safety valve by means of said connection means in said drilling area substantially aligned with the axis of said drilling tower; - coupling means mechanically mounted on said overhead crane and movable between an engagement position, in which said coupling means retain said safety valve, and a disengagement position in which said coupling means are released from said safety valve; said overhead crane being susceptible of being moved along said at least one rail between said parking area, in which said overhead crane supports said safety valve in raised position, and said drilling area, in which said overhead crane supports said safety valve above said drilling area with said lifting winch mechanically connected to said safety valve and said coupling means in engagement position; said crane and/or the lifting winch of said overhead crane being susceptible of displacing said safety valve from said raised position to a lowered operative position in said drilling area with said lifting winch and said crane connected to said safety valve and with said coupling means in disengaged position. - a support structure, intended to be installed on said watercraft and comprising at least one resting platform and at least one suspension platform placed at the top part spaced with respect to said resting platform; - lifting means mechanically mounted on said resting platform to support said safety valve, and movable between at least one lowered position, in which said lifting means support said safety valve in proximity to said resting platform, and a raised position, in which said lifting means support said safety valve in proximity to said suspension platform; - at least one rail mechanically associated with the suspension platform of said support structure and extending along a transfer path intended to connect a parking area to a drilling area susceptible of being associated with the drilling tower of said watercraft; - at least one overhead crane slidably mounted on said at least one rail along said transfer path, and comprising at least one lifting winch susceptible of supporting said safety valve in said parking area above said lifting means; - at least one crane provided with connection means, mounted at said drilling area and susceptible of supporting said safety valve by means of said connection means in said drilling area substantially aligned with the axis of said drilling tower; - coupling means mechanically mounted on said overhead crane and movable between an engagement position, in which said coupling means retain said safety valve, and a disengagement position in which said coupling means are released from said safety valve;