Rayna.........have a study of the carriage that gribeauval posted.
1) the four loops that are on te two "black" skids were/are for holding the boat onto the carriage via quick release slip links , and are disconnected on launch by four crewmen simultaniously hammering out the slip pin holding the boat to the carriage.
just before launch, the black skids on which the bilge skegs of the boat are sat, raise at an angle for the boat to launch, and the boat launches down the skids which form the "launching slip"...........please note that the tracters that drive these launching carrieages are completely watertight and can go off the beach until they are almost submerged.
On retrieval of the boat the boat actually drives itself onto the beach, rolling skids are put under the keel and she is drawn back onto carriage via a powerfull winch mounted on the tracter, and fed through Ruffle holes in the boat's deadwood at either bow or stern.
look at some pics on google/youtube and you'll be able to see the process.
neil.