A movable platform unit (1) for a boat (B), in particular for launching or hauling out a tender or the like, includes a base portion (2) secured to the boat (B) and at least one swing arm (32a, 32b), pivoted at one end onto the base portion (2) and at the other to a load platform (3). The swing arm (32a, 32b) can be rotated by a first drive member (57) secured thereto and rotatable about the axis (x) about which the swing arm (32a, 32b) is pivoted on the base portion (2). Alignment means (67, 68) are provided for connecting the load platform (3) to a second drive member (65a) secured to the base portion (2) and coaxial with the axis (x) about which the swing arm (32a, 32b) is pivoted on the base portion (2) so as to enable the platform (3) to maintain a constant inclination to the base portion (2) during rotation of the swing arms (32a, 32b)