DESIGN

The importance of having a properly designed exhaust cannot be over-emphasised. As funnels are not usually a practical proposition on leisure craft, virtually all small commercial passenger vessels, small sailing vessels and motor boats below 30m have a ‘wet’ exhaust system running inside the hull. The exit is normally on, or close to, the waterline, generally right aft, but is increasingly under the waterline on modern displacement and planning cruisers.

Clearly boats require special exhaust systems to avoid the dangers of running hot exhaust gases through the accommodation and the added challenge to the confined space available to accommodate the necessarily large metal muffler to silence a dry exhaust system, a wet system is hugely efficient at cooling the hot exhaust gases and far more space efficient making it the appropriate solution for marine engines and this is where Halyard’s area of expertise is based.

There are three key considerations in the design of a ‘wet’ or ‘water injected’ exhaust system.

To reduce noise by between 40% to 90%
Introducing water into the exhaust increases the ‘back pressure’ that the engine has to overcome to force the exhaust gases out. Engine manufacturers set back pressure limits which combined with gas flow rates determine the system size that is required.
When the engine is running the outward flow of gas from the engine prevents water getting back into the engine, but with the engine stopped, it is critical that water cannot travel back through the exhaust system into the engine. If that happens it will create a Hydraulic lock in the engine, which is likely to destroy the engine.

Our designers understand these parameters and are all specialists in exhaust design. The key for us is to understand exactly where the engine is located in respect to the waterline and the likely exhaust run to the outlet so we can determine the best solution for your specific installation. Examples of systems required for a given waterline »