What is "capstans"

Usage examples of "capstans".

It had spent long enough jutting over the ocean, lifted on a framework to keep it clear of the deck’s little capstans and bulkheads.

They looked in bewilderment at lines and spars, down fathoms of deck to the harpoon catapult, capstans, bowsprit, and back at the sailors.

At home there were ratcheted capstans outside every lodge, so that as little as four women could bring down a rover.