Abstract: A clamp for securing a boat with integral oarlock receptacles in an inverted position on the roof of a motor vehicle. The clamp apparatus includes a bolt member that is positioned in an oarlock receptacle, a clamp assembly that can be releasably secured to the motor vehicle's rain gutter or other latching part and extensible and contractible coupling means which extends between and is connected to the bolt member and the clamp assembly. The coupling means can be contracted to draw the bolt member toward the clamp assembly thereby to secure the boat to the roof.