More than your ordinary umbrella, this Square Boat Umbrella has been manufactured for use in the harsh of marine environment. Made with non-corroding, fade resistant acrylic nylon materials, the windproof design will not allow the canopy to turn inside out or lose its shape in gusty wind conditions. The umbrella shade reduces the temperature under the canopy, keeping you and your guests out of the harmful sun’s rays while the four corner tie-down securing points and quick release round rail mount make adjustment a breeze in creating an extremely secure shaded area. The silver color is 100% UV blocked, for added protection.  Umbrella can be used with or without the included (4) tension cords for extra support in windy conditions. The umbrella’s square shape measures 6ft. (1.8m) across the bow with a 5 ft. (1.5m) fiberglass shaft assembly. The canopy is stretched over specially designed fiberglass bow ribs that will not rust or stain the fabric while the main shaft is constructed of flexible double-cored fiberglass for extra strength. The included round rail mount is made of 18-8 Stainless Steel and 356 Hard Anodized Aluminum, to fit vertical stanchions or horizontal railings and quickly detaches without tools leaving no hardware on the rail.