Chapter 9:Dry Exhaust Systems
Figure 9-16. Alternate condensate drain
Collecting and Draining
Spray and Condensation
Regardless of how high and how well installed
the exhaust outlet opening is, some rain and
spray may get in. Additionally, the long pipe
has a considerable interior surface area that
will generate condensation. All of this mois-
ture must be kept from entering the engine, es-
pecially the turbo. For this reason a sump, or
trap, should be installed at the lowest point in
the vertical exhaust outlet pipe to collect
spray and condensation, and it should be fitted
with a drain plug to clear any standing water.
You can see this in the basic drystack exhaust
system illustrated in Figure 9-1. Note: A water
sensor at the trap capable of withstanding
high temperatures is recommended.
Alternatively some installations use a
simple 90-degree elbow with a drain plug at
the bottom (Figure 9-16). Though this has
proved adequate in some installations, I rec-
ommend against it, as there really is no con-
densate sump to collect water.
Insulation or Lagging
Every bit as important is the insulation or lag-
ging that protects the crew and the boat from
burns and fire and reduces heat radiated into
the vessel’s interior. The terms insulation
andlaggingare used interchangeably in this
application, but lagging is more specifically
a semipermanent insulation wrapped around
the piping, frequently sealed with a hard-coat
surface. Insulation, in general, includes such
lagging, but also includes moderately flexi-
ble and removable blankets, fabricated
“boots,” and pads, as well as the insulation in-
stalled on the boat structure itself.
Either hard-coat lagging or blanket-type
insulation may be used as convenient. The ex-
ception is at the flexible bellows, where the
insulation also must be flexible. Here, remov-
able flexible insulation blankets (configured
to wrap around and lace or hook closed) must
be used (Figure 9-18). Similarly, care must be
used at expansion slip joints, as well as at
clamps and pipe hangers, to ensure that a
hard-coat lagging doesn’t restrain motion. Us-
ing removable blankets, wraps, or “boots” at
these fittings also makes inspection, replace-
ment, and repair much easier. Figure 9-17
shows a well-insulated pair of dry exhausts.
You can see the removable blankets/boots
over the flexible bellows and critical joints.
The photo of the muffler/silencer insulation
blanket in Figure 9-19 shows the components
of such removable blankets.
High-temperature insulation used to be
easy, as one material virtually did it all: as-
bestos. As a child, I can remember going with
my father to the local hardware store andFigure 9-17.
Well-insulated
dry exhausts
(Courtesy Detroit
Diesel)