Some booms allow for roller furling of mainsails. These boats used conventional gaff mainsails and jibs, attached to the mast by travellers. Performance yachts are likely to have full-battened kevlar or carbon-fiber mainsails. This is especially true of mainsails and high aspect jibs. Boom furling mainsails also must deal with the issue of the leading edge. "Nancy" was 67 tons burthen with two raked masts, square topsails and fore-and-aft mainsails. The ship has one of the largest mainsails in the world, measuring . Mainsails are often self-tending and slide on a traveler to the opposite side.