Ketch mizzen sheet. So on a ketch, the dual purpose of the mizzen sail is to both propel and balance the vessel, while on a yawl, the smaller mizzen mainly serves the purpose of trim or balance. Yawls tend to have mainsails almost as large as those of comparable sloops. A ketch may be distinguished from a cutter or a sloop by virtue of having two masts rather than one, though a ketch with two foresails is sometimes called a "cutter-rigged ketch". Both the ketch and the yawl differ from the two-masted schooner, whose aft mainmast is taller than the foremast.
Radio masts and towers for research to find ways to minimize the hazard that communications towers can pose to birds. There have also been instances of rare birds nesting in cell towers and thereby preventing repair work due to legislation intended to protect them. Since June 2010, Telecom operators in the USA can erect new telecom masts or towers as the government has lifted the moratorium, which was earlier placed on the issuance of permits for the construction of telecommunication towers. Radio masts and towers Radio masts and towers are, typically, tall structures designed to support antennas (also known as aerials) for telecommunications and