Propitiation of the Gods
On launching a ship in modern times a sacrificial bottle of champagne is smashed against the hull to christen the vessel. Champagne is used as a fine drink of celebration, though other drinks are sometimes used. The Queen recently used a bottle of whiskey to launch the aircraft carrier HMS Queen Elizabeth. Before champagne, red wine was used to symbolize the blood of pagan sacrifices. In England a precious metal, loving cup, full of red wine was thrown overboard, and caught by a lucky attendee. This became a bottle as the number of ships launched made it too expensive to throw precious metals overboard.
More can be found about launching ceremonies - here.
In ancient times the launching of a ship required the propitiation of the gods of the sea, such as Neptune. For many cultures an animal sacrifice sufficed, but some cultures seem to have placed more importance on ships and the sea than others. The Anglo-Saxons and Vikings for instance, sometimes included ships in their burial mounds. The ship would have gone with the deceased to the afterlife along with other offerings. During the 7th Century the Anglo-Saxons were rapidly converting to Christianity; but before this they shared the same religious practices as other Germanic people and were just as fierce coastal raiders and pirates as the Vikings. There is some evidence the Anglo-Saxons practiced human sacrifice but it is considered debatable.
The Vikings at least are said to have placed sacrificial victims on the slipway used to launch ships. They would be crushed as the ship was launched and the ships keel wetted with the blood. It sounds a rather sticky way to launch a ship but the Maori and Fijian’s also used such sacrifices to launch ships.
The Cannibal Islands, Captain Cook’s Adventure in the South Seas
"Ellis tells us that the bodies of men slain in battle were usually left to be devoured by the hogs and wild dogs. This was doubtless the case in some of the groups of islands where cannibalism was perhaps not very much practised, but in other groups—especially among those known by the name of the Feejees—the slain were more frequently devoured by men and women than by hogs or dogs. The victors used to carry off the lower jaw-bones of the most distinguished among the slain as trophies, and also the bones of the arms and legs, from which they formed tools of various kinds and fish-hooks, and the skulls they converted into drinking-cups. The dead bodies were sometimes laid in rows along the beach, and used as rollers, over which the canoes were launched."