They are primarily powered by sails and use a lateen-rigged sail pattern not understood outside of the Isles but which propels them across the waves swifter than nearly every ship in the world. They are designed to withstand the wave and weather conditions of the Cuananiar Ocean, which are often quite challenging.
They are fairly large ships, usually more than 100 feet long, 20 feet in beam, and over 300 tons. Nevertheless, they're fast, usually more than 8 knots, and have a fairly shallow draft, usually less than 10 feet. Their crews are usually 80-90 sailors.
Because of their large size, they can combine sizable cargo space (usually 120 tons or more) with powerful armaments, normally ballistae fore and aft. In addition to their crew, they regularly carry around twenty marines, each armed with powerful bows and other weapons. Their sailors can also fight, and it is rare for a morcurrach to be defeated by a single vessel from another realm, though there are Svellheimish crews and longships that can match them.