A bottom-dump vessel, whose longitudinal hull sections can be pivoted apart by jack means to provide an open bottom for discharge of cargo, has the adjoining edges of the keels of the hull sections interconnected by articulated rods which in substantial side-by-side position loch the hull sections in the closed position and in substantial end-to end position limit the angle of opening of the hull sections. The locking rods have means for positively driving them, thereby allowing for rapidly opening the vessel and transmitting appropriate braking forces to cope with mass forces. The arrangement makes for moderation in the size of jacks and other facilities required.