Riser

In the case of boat exhaust manifolds, exhaust gas cooling occurs in the riser where the gas is mixed with water. The cooling water is injected into the exhaust pipe through the riser and it is here that water-exhaust gas mixing occurs. Various methods are used to make risers. Normally, during manufacture, account must be taken of the exhaust gas flow, space velocity and quantity of coolant. To protect the riser against corrosion, zincs are normally used. To make risers, in view of the particular job they have to do, AISI 316L stainless steel is normally used; other materials would undergo quick corrosion caused both by the seawater and by the high temperatures of the exhaust gases. Very often, the risers are customised, designed and manufactured to specific requirements inasmuch as the fitting and positioning of the riser in the exhaust system must be extremely precise to ensure correct operation. Standardised risers also exist on the market that have to be adapted and integrated in the boat’s exhaust system.