Marine Exhaust Systems - How They Work

Marine exhausts systems are an important andensured it works. To remove water from inside
often overlooked part of a marine engine. Mostthe combustion chambers, first remove all
vessels have a 'wet' exhaust system. Salt waterinjectors, crank engine over to blow water out,
is injected at the riser - the outlet for exhaustrefit injectors, bleed injector lines, and start. Then
from the exhaust manifold. This mixture ofleave motor running until exhaust sorted out.
exhaust gas and water is then passed through aCheck to see that the riser is not coked up or
series of bends until it exits the boat, preferablycorroded - a common problem. To check the
at the stern.exhaust riser remove the exhaust hose from the
Exhaust gases mixed with salt water create ariser (often a difficult procedure) and look up the
highly corrosive compound. This is why exhaustpipe to see if it is restricted by exhaust/salt build
systems are commonly made using non-corrosiveup. If build up is excessive the riser will have to be
components such as nitrile rubber reinforced hoseremoved to check the engine end of the pipe.
(brown - not green - stripe), galvanized steel,Coke can be scraped out to provide a short term
fiberglass or plastic. The purpose of thesefix although often the riser will have to be
components, which vary in size and shapereplaced. There are aftermarket systems which
depending on the engine size and layout of thevary in quality. Make sure you fit the right design
engine room, is to prevent hydraulicing of thefor the application.
engine. This is caused when an engine has filledEnsure your water-lock is low enough and big
with salt water which has entered via the exhaustenough to hold all the water in exhaust system. Is
and can cause extensive damage if left for morethere a gooseneck or central vertical loop in the
than two hours. Water enters the exhaust fromexhaust hose at the transom exit? Is there a
wave action at stern and poor exhaust design. Insiphon break and is it functioning properly - no
some ocean conditions, such as a following sea,leaking valves?
water can be forced back up the exhaust whenExhaust gas is poisonous and can cause sea
the engine is not running. Poorly designed exhaustssickness and headaches. Replace any faulty parts
allow water to flow back and fill the waterlockimmediately. Use double hose clamps on each joint
muffler box then up the hose into the exhaustor, preferably, super clamps, bolt style, and
manifold, through the exhaust valves and into theexhaust cement if need be. Hot sections should
combustion chamber. With the engine full of waterbe lagged with fiberglass tape to prevent burns.
the engine cannot crank over as it is cannotBeware of asbestos lagging. Many older vessels
compress water.and marine engine installations had exhaust
You will know your engine is hydrauliced if it willsystems that were lagged with asbestos tape
not turn over - generally after a long sailing periodand rope. Asbestos sound-proofing was also
- and you have removed the starter motor andcommon in older boats.