Currachs in general adhere to a plan designed to produce a sturdy, light and versatile vessel. The framework consists of latticework formed of rib-frames ("hoops") and stringers (longitudinal slats), surmounted by a gunwale. There are stem and stern posts, but no keel. Thwarts are fitted, with knees supplied as required. Cleats or thole pins are fitted for the oars, and there may be a mast and sail, though with a minimum of rigging. The outside of the hull is covered by tarred canvas or calico, a substitute for animal hide.