The optional 18" (45.7 cm) coils greatly increase the versatility and enhance the capabilities of the Pulse 6X or 8X Metal Detectors. For instance, this coil is designed for boat deployment. Sit in the boat with the detector's electronicsunit, put the coil with its 100' (30.5 meters) cable over the side, and you can search for anchors, cannons, outboard motors, etc. Coil can be mounted on a sledand towed across the bottom. Coil is depth rated to 200' (61 meters). As with all other Fisher Products it comes with a two year warranty.