Complex sentence: She carried square sails on both masts, but had a small trysail mast (also called a snowmast) stepped immediately abaft the mainmast from which a trysail with a boom was set, with the luff of the trysail hooped to it.
Split into simpler sentences: She carried square sails on both masts, but had a small trysail mast (also called a'snowmast') stepped immediately abaft the mainmast. This mast could carry a trysail with a boom, with the luff of the trysail hooped to it.