Marine exhaust systems are actually fairly complex systems: much more complex than a layman would think. They are simply the “tailpipe” of the boat, right?
This misconception is often a problem. One critical part of the vessel exhaust system is the exhaust risers, and these can often fail. The function of the riser is two fold:
- They keep water from backing up into the engine.
- They channel cooling water to the engine.
The design of the exhaust riser is critical, and is a situation where it often is beneficial for the engine manufacturer and the shipyard or naval architect to work closely together. If the angle of the riser is incorrect, or it is modified, water can accumulate, leading to bad corrosion issues. Poor design, especially with aftermarket additions or modifications, can also create serious back pressure problems on the engine, greatly impacting engine performance.
Water and metal do not mix well. This is why the gaskets and the risers should be frequently inspected and replaced if necessary. Even in cases with no leakage, the risers should be removed and periodically cleared of any rust or scale that may have formed.
Some engine manufacturers provide risers with the engines, and other do not (they are optional with Marinediesel). In some cases, they must be custom designed in order to fit into an engine compartment. In any event, there is a golden rule with exhaust risers: NEVER use aluminium risers. Yes, they are cheap, and risers can be one of the more expensive components to buy, but they are short on life span and can cause serious problems over the life of the engine.