Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

In this system, no raw water enters the
engine block, only the antifreeze/freshwater
coolant mixture. This closed system is effi-
ciently temperature-controlled by the ther-
mostat, and it keeps all raw water out of the
engine. It does require two water pumps
though: the water pump on the freshwater or
closed-cooling circuit, and another pump on
the raw-water circuit. Where there is an after-
cooler or intercooler, separate heat exchang-
ers are usually used for each (Figure 8-5).

Keel Cooling

Last, there is keel cooling. It is not new. In fact,
steamboats in the 1840s used external con-
densers (effectively what we call keel coolers)
mounted outside the hull. In keel cooling, there
is no raw-water cooling circuit. Instead, the en-
gine heat exchanger is placed outside the boat
in contact with the sea. The seawater thus di-
rectly carries away the engine heat. This elimi-
nates a raw-water pump and salt water in the
boat, but you now have no raw water to cool
the exhaust, which—as we’ve seen—is danger-
ously hot. The exhaust is now entirely a dry ex-
haust (or drystack exhaust), and it is at a very
high temperature indeed. We’ll cover the instal-
lation of these drystack systems in Chapter 9.
Before we move on to the exhaust piping
itself, we need to look at the keel cooling

that drystack exhausts require. Keel cooling

is an integral part of a drystack exhaust sys-

tem. Further, on heat-exchanger engines,

most of the cooling package (minus some

hose, a seacock, and raw-water strainer or

sea strainer) comes as a package with the

engine. In contrast, much of the keel-cooling

Chapter 8: Engine Cooling Systems and Their Exhausts

Figure 8-4. Heat-

exchanger cooling:

jacket water after-

cooled (Courtesy

Caterpillar, Inc.)

Figure 8-3.

Radiator cooling

(Courtesy

Caterpillar, Inc.)