the coop of the counter?

[Mher]

Is there any idea about this? "My brother was at the stern, holding on to a large empty water-cask which had been securely lashed under the coop of the counter . . .. "

 

[Grumpy]

The rear end of a ship or boat is called the "Stern", and a "Counter Stern" is a particular type. In this case, instead of having a flat stern, which descended vertically to the surface of the sea from where the writer's brother was sitting, the stern would have descended vertically for a distance, then sloped inwards towards the bows of the ship, forming an overhanging (ie counter) stern. The sloping bit is called the "Counter", and the water-cask would have been hanging from this handy "ceiling" above the water line. I presume that "coop" refers to the shelter/shade/enclosure afforded by the counter.