Mercury 60930 Quicksilver Water Shutter, Water Flapper for Numerous MerCruiser Sterndrive Installations MELSTER3 each with advanced localized menu each with advanced localized menu controls Dual radar support allows each of your compatible chartplotters on your boat to pull data from one of two different radar sources to provide redundancy It has earned a loyal following by providing the highest quality products that are tested through some of the most rigorous environments and testing procedures the shutter is open for exhaust to exit the engine and closes when the engine is not running to keep water from flowing back to the engine causing corrosion or serious damage to the engine