The “Threads” model has a threaded portion inside the boat and a big nut that is screwed down tight to the stainless steel backing plate that is provided. This is very similar to most other thru-hull fittings including instrument transducers, water intakes and discharges. It requires a large wrench be swung with a fair amount of force in a large radius. Unless the exterior portion is held steady, the whole fitting will tend to rotate as the nut is tightened.

The “Studs” model has two studs that protrude from the top of the interior portion of the fitting. A stainless steel bar is slipped over the studs, followed by a washer and nut. There is a selection of different size collars provided (to accommodate different hull thickness). The appropriate one is chosen and then installed between the bars & the stainless steel backing plate that is provided. The two nuts can now be gently tightened with a 1/2” socket. This advantages of this fitting arebq. that it can be installed in a tight area where there is not room to swing a wrench, and there is no need to restrain the fitting as it will not rotate when tightened.

The keel cooler is available with sacrificial zincs, which is not necessary in normal applications, but may be required if the boat has a “floating ground” system.

Both types (“Threads” & “Studs”) are available with two, circular, flush mounted sacrificial zincs installed in the bottom. These models are identical in size & shape to the non-zinc types. Most modern boats will have a bonding system that essentially connects bronze thru-hulls electrically to each other and to a sacrificial zinc anode that is mounted either on the prop the shaft or the hull, & is also connected to the battery negative. The higher voltage of the zinc protects the other thru-hull fittings, and slowly sacrifices some of its metal. The sintered bronze & cupro-nickel that is used in the construction of the keel cooler is compatible with other marine-grade bronze and brass fittings. As the keel cooler must be connected to the battery negative (as a safety precaution), the fitting will normally be protected by the boats shaft or hull zinc. If the boat has no bonding system or has non-metallic fittings and all thru-hulls and the prop shaft are electrically isolated (there will still be shaft or prop zinc), then the installation of a keel cooler with zincs is recommended because the fitting will be connected electrically to the battery negative, thus any stray or corrosion currents can use this path.

There is no difference in performance between a keel cooler with zincs or without zincs. If one is installed with zincs in an application that does not require them, the zincs will still erode and will require changing periodically. In all cases, we strongly recommend the use of a temporary “guppy” zinc while the boat is at the dock or on a mooring, and the installation of a “Zinc Saver” or similar device.

Zincs are not required on boats with bonding systems.