A system for deploying buoyant equipment onto a support structure located on a bed of a body of water, the support structure having a support surface for receiving such equipment, and an engagement portion having a circular engagement aperture having a diameter, the system comprising: a winch device adapted for releasable mounting on such equipment, the winch device having a winch tether that extends therefrom, and being operable to pay out and to winch in the winch tether, and a coupling device attached to a distal end of the winch tether for releasable engagement with an engagement portion of such a support structure, wherein the coupling device has a first position in which the coupling device has an outer dimension greater than the diameter of such engagement aperture of the support structure, and a second position in which the coupling device has a maximum outer dimension less than the diameter of the engagement aperture of the support structure, the coupling device comprising: a circular body portion having an upper surface, and having a diameter smaller than that of the engagement aperture; a tether engagement portion attached to the body portion, the tether engagement portion being attached to the distal end of the winch tether; characterised by a locking portion, rotatably attached to the body portion, and having a first position in which the locking portion extends substantially parallel to and adjacent the upper surface of the body portion, and a second position in which the locking portion extends away from the upper surface of the body portion in the direction of the winch tether, wherein, in the first position, the locking portion overhangs an outer edge of the body portion such that the coupling device has an outer dimension greater than the diameter of the engagement aperture of the support structure, and wherein, in the second position, the coupling device has a maximum outer dimension less than the diameter of the engagement aperture of the support structure. a winch device adapted for releasable mounting on such equipment, the winch device having a winch tether that extends therefrom, and being operable to pay out and to winch in the winch tether, and a coupling device attached to a distal end of the winch tether for releasable engagement with an engagement portion of such a support structure, wherein the coupling device has a first position in which the coupling device has an outer dimension greater than the diameter of such engagement aperture of the support structure, and a second position in which the coupling device has a maximum outer dimension less than the diameter of the engagement aperture of the support structure, the coupling device comprising: a circular body portion having an upper surface, and having a diameter smaller than that of the engagement aperture; a tether engagement portion attached to the body portion, the tether engagement portion being attached to the distal end of the winch tether; characterised by a locking portion, rotatably attached to the body portion, and having a first position in which the locking portion extends substantially parallel to and adjacent the upper surface of the body portion, and a second position in which the locking portion extends away from the upper surface of the body portion in the direction of the winch tether, wherein, in the first position, the locking portion overhangs an outer edge of the body portion such that the coupling device has an outer dimension greater than the diameter of the engagement aperture of the support structure, and wherein, in the second position, the coupling device has a maximum outer dimension less than the diameter of the engagement aperture of the support structure. a circular body portion having an upper surface, and having a diameter smaller than that of the engagement aperture; a tether engagement portion attached to the body portion, the tether engagement portion being attached to the distal end of the winch tether; characterised by a locking portion, rotatably attached to the body portion, and having a first position in which the locking portion extends substantially parallel to and adjacent the upper surface of the body portion, and a second position in which the locking portion extends away from the upper surface of the body portion in the direction of the winch tether, wherein, in the first position, the locking portion overhangs an outer edge of the body portion such that the coupling device has an outer dimension greater than the diameter of the engagement aperture of the support structure, and wherein, in the second position, the coupling device has a maximum outer dimension less than the diameter of the engagement aperture of the support structure.