The FORESPAR 1 1/2" Barbed Thru Hull is for use above or below the waterline, Marelon™ Mushroom Head Thru-Hull Fittings with Hose Barb are designed for years of trouble-free use, easy installation and quick attachment of hoses. They are extremely durable, strong and unlike heavier bronze fittings, not subject to galvanic corrosion.