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

PART THREE:EXHAUST SYSTEMS

Figure 9-14.
Flexible bellows
with directional
turbo liner
(Courtesy
Applegate
Industrial
Materials, Inc.)

cause a failure. (The bellows are available in

both weld-in and bolted-flange styles.) The

bellows also cannot support any weight, nei-

ther axial nor transverse loads. You can see in

Figures 9-1, 9-6, and 9-23 that the weight of

the pipe or the muffler is taken by the brack-

ets, not the bellows. These bellows really

need to be babied on installation and to be

well protected from dings, scratches, gouges,

and foreign material during their installation

and their service life.

In the old days of naturally aspirated en-

gines, the flexible bellows were usually un-

lined. This is still acceptable for cabin-heater

exhaust systems or for a naturally aspirated

engine. Today, however, almost all engines

and generators are turbocharged. All the bel-

lows in the system must have an internal

turbo liner or turbo shield. These are direc-

tional, as you can see in Figure 9-14. They are

welded to the inside of the bellows at one end

and open at the other so the bellows will

remain flexible. This is why the bellows are

directional. The welded-on, sealed end must

be installed toward the engine. The result

is a “shingle” effect as the exhaust gases

pass through the bellows smoothly, without

making direct contact with the inside of the

exterior bellows itself. If you install the

turbolined flexible bellows backward, it will

cause turbulence, added back pressure, and

ultimately a failure.

There’s another important consideration

here. You can see how close the clearance is

between the interior turbo liner and the ex-

terior bellows. This means that there is very

little lateral (side-to-side) movement possible

when using bellows with turbo liners. You

have to line up the bellows as close to dead

center on the exhaust pipe axis as possible.

You cannot rely on the bellows with turbo lin-

ers to accept much side-to-side deflection or

to make up for any misalignment at all.

Flexible Exhaust Hose

for Dry Exhaust

Though bellows are most common for dry ex-

haust installations, the limitations just noted

means that a very flexibly mounted engine

(such as an engine on an Aquadrive installa-

tion) should use a length of flexible stainless,

dry exhaust hose (Figure 9-15) between the

engine-exhaust outlet and the exhaust pipe.

This hose is a woven sleeve of stainless wire

and flat strands. The flexible hose can absorb

more motion in more directions than flexible

bellows.

Figure 9-15. Flexible-steel dry exhaust hose

(Courtesy Volvo Penta)