There are four main objectives for the marine exhaust system:

* To reduce noise between 40% and 90%
* To cool the exhaust, and eject the engine cooling water through the exhaust without excessive back pressure
* To minimise the risk of water returning back up the exhaust system and into the engine cylinders causing serious damage
* To site the outlets at the stern of the boat to minimise exhaust fumes on board

Noise Reduction

A typical installation of the single chamber lift silencer, this type of exhaust system offers a noise reduction of up to 40%.

Further information on Halyard’s Lift Silencer

The standard inline exhaust system would offer a noise reduction of up to 40%.

Further information on Halyard’s Inline Silencer

The dual chamber silencer will offer a 80% noise reduction.

Cooling
The second important part of the exhaust system is to inject the cooling water from the engine into the exhaust system without causing any issues with restrictions to the gas. The reason why we use water injection into the exhaust system is that we are able to use more modern material such as GRP. Other advantages are that the hot dry pipes that could be in excess of 400°C are reduced to a minimum temperature thus eliminating the risk of someone injuring themselves on a dry exhaust system. The important part of specifying a wet exhaust system is to choose the correct diameter to avoid back pressure problems.

Water separation
The third important part of the exhaust system is to reduce the risk of water returning back to the engine cylinders. If sea water were to find its way to the engine end of the exhaust system, there would be nothing to stop it entering the exhaust manifold and from there, getting into the cylinders themselves through any open exhaust valves. With cylinders full of water you can imagine what would happen when you innocently turned the key for the next start. The technical term “hydraulic lock” may sound fairly innocuous, but can mean bent or broken connecting rods, collapsed pistons and wrecked bearings.

Installation and operating instructions for Halyard’s Water Separators and detailed diagrams.

Exhaust positioning
The fourth part to the exhaust system is to position the exhaust outlet on the transom of the boat, the reason for this is to pull the fumes away from the boat, one other important part of the exhaust outlet is to fit a transom flapper this will prevent a following sea filling the exhaust system up with sea water.