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Guide
To Choosing Keel Coolers; "Studs" vs "Threads"
Zincs or no Zincs
Stud
fitting (PN E50722) VS Thread fitting (PNE50361)
Both of these keel coolers require a 1 1/2" hole for mounting,
& the "exterior" parts are identical. The
"Threads" model has just that, a threaded portion inside the
boat & a big nut that is screwed down tight on to the stainless
steel backing plate that is provided. This is very similar to most
other thru-hull fittings including instrument transducers & water
intakes & discharges, and it requires that a large wrench be swung
with a fair amount of force in a large radius. Unless the exterior
portion is held steady by either jamming in pieces of wood or by a
strong helper, the whole fitting with 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, & over each of these is slipped a
stainless steel bar followed by a washer & nut. There is a
selection of different size collars provided (to accommodate different
hull thickness), & the appropriate one is chosen & 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 are that it can be installed in
a tight area where there is not the room to swing a wrench, & there
is no need to restrain the fitting as it will not rotate when tightened.
Zincs
or No Zincs? PN E500722Z) & PNE50361Z
Both types of keel cooler,
"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 & are
distinguished by a "Z" following the Part Number. 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 & 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-metalic fittings& all thru-hulls &
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, & 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 & 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,
& the installation of a "Zinc Saver" or similar device.
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