INCREASINGFLOWSPEED INLARGECHANNELS
If structural shapes like U channels are used
to fabricate a keel cooler, you may find that
flow speed is too low. This can be corrected
by welding in right-angle partial “baffles” or
plates that close off, say, two-thirds of the
opening. The openings in the baffle plates
will alternate from side to side so the flow
follows a roughly zigzag pattern. Though this
is a standard fix for builder-fabricated keel
coolers, it almost always seems better to me
to use a manufactured keel cooler, where
such work-arounds aren’t required.
KEEL-COOLERAPPENDAGEDRAG ANDFAIRING
THEKEELCOOLER The keel-cooler piping
outside the hull creates additional drag. On
slower displacement vessels, this can be toler-
ated without fairing, but it’s always better to
fair the keel cooler (Figure 8-11). (The fairing
also protects the cooler from damage.) If the
cooler is mounted on the outside of the hull
surface, it can be faired with tapered blocks
or wedges to smooth the water flow over and
around the front and back of the cooler.
It is even better to build a recess into the
hull so the cooler can be mounted flush. The
outer face of the cooler should be recessed
about^1 / 2 inch (12 mm) in from the outer sur-
face of the hull and have a clearance of about
(^11) / 2 inches (38 mm) around the sides of the
recess.
Metal vessels with somewhat squarish
midship sections can also install the keel
cooler inside a walled-off box at the side of
the hull near the turn of the bilge. This is
functionally the same as being in a box keel,
with openings to the sea at the bottom and
sides of the box. This configuration is some-
times termed a box cooler (Figure 8-12).
On metal boats with box keels, the keel
cooler can be built into the box keel itself. In
this location, it’s virtually invisible and cre-
ates no additional drag. The box keel must
have numerous opening holes along its bot-
tom and the sides at the top, so seawater can
flow through them and around the keel-
cooler tubes freely.
MANUFACTURED KEEL COOLERS Though
builders can fabricate a keel cooler using the
previous cooling-area guidelines, in most in-
stances premanufactured keel coolers from
companies like R. W. Fernstrum and Walter
Machine Co. (Figure 8-13) are both more
compact and more efficient. These are al-
most universally made of copper-nickel, and
the manufacturer will provide sizing and in-
stallation guidance. Fernstrum also makes
keel coolers of 5000-series aluminum. Only
aluminum keel-cooler components should be
used on aluminum hulls to avoid corrosion
problems (though cleaning and painting with
antifouling is a chore). Even on steel hulls,
great attention must be paid to isolating the
keel cooler and its piping from the steel. The
manufacturer’s installation kit and instruc-
tions cover this in detail.
SPECIALKEEL-COOLERTUBESHAPES Most
commercially made keel coolers don’t use
simple, straight round tube. Instead, they use
square tube, which has more surface area for
a given inside cross-section area, or fluted or
Chapter 8: Engine Cooling Systems and Their Exhausts
Figure 8-11. Keel
cooler fairing
(Courtesy R.W.
Fernstrum & Co.)