A 6" diameter Halyard stainless steel exhaust riser.
Note the water injection point and the swivel joints that allow the riser outlet to be adjusted in three dimensions for optimum convenience.
 

Medium Level Engines
If the engine is mounted on or about waterline level, it may be necessary to fit what's known as a riser to the exhaust manifold or turbocharger outlet to artificially lift the engine end of the exhaust to provide a proper gradient. Risers incorporate a spray ring to ensure better mixing of water and gas which helps all-round cooling of the exhaust pipe circumference.

From the riser outlet aft, the system is essentially the same as for the high mounted case and the same considerations regarding silencer inclination and transom outlet apply.
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Exhaust Configurations