Yachting Monthly 0shares Some sailors swear by mainsail furling systems, others swear at them. Graham Snook looks at way to keep your furling mainsail in check In-mast furling mainsails (left) have evolved significantly, and vertical battens allow more roach and better sail shape. Credit: Graham Snook Mainsail furling systems have come on a long way. Sails no longer need to be wrapped around a boom, nor does an in-mast mainsail need to be the hollow-leached, baggy triangle we first saw decades ago. Furling mainsail systems can now offer more sail area than a traditional slab-reefed mainsail. Be that as it may, every slab-reefed sailor knows a horror story about in-mast or in-boom furling that is enough to make them steer well clear, while those that have furling mains wouldn’t put to sea without one.