The combination of silicone bronze, naval brass and stainless steel used on a retractable keel boat is a virtual battery just waiting to be damaged by galvanic corrosion. Zinc, being the least noble of any of the metals used under water on your retractable keel boat, corrodes first thereby protecting all the other metals.
In order to protect the metal parts, a zinc must be electriclly connected to the metal that you wish to protect. There is no easy way to insure electrical contact by bolting directly to the fiberglass keel. Therefore this zinc is installed by through bolting it to the outside of the hull. It is electrically connected to the keel via an electrical wire. One end of the wire is connected to the zinc's mounting bolt inside the boat, the other end to the keel winch using one of the winch mounting bolts. Since the keel cable is connected to both the keel winch at the top and the keel's stainless steel backbone at the bottom, all metal components of the keel and pivot assembly are protected. Complete kit.