Safety first
Although from the owner's point of view, the silencer's main job is to make life quieter, a well-designed silencer will enhance safety enormously by making it very difficult for water sloshing up the exhaust pipe to get anywhere near the engine. Different types of silencer are more or less effective in this respect. So when deciding which type to fit, the characteristics of the entire exhaust system must be taken into account. The right type of silencer can not only quieten the exhaust noise considerably, but also help overcome potential siphoning and other problems in one fell swoop.

Positioning
The ideal position for a silencer is about 39in (1 m) behind the exhaust outlet or riser. The further back it goes, the less effective it is. However, it is often difficult to locate the silencer that far forward.

Fifteen years ago it was unusual to find a boat fitted with a silencer, these days it's rare to find a leisure craft without one. This is partly due to our increasing desire for a quiet life, and part because modern marine diesel engines rev much higher, with a much more aggressive exhaust note.

lnline mufflers
The simplest type of silencer is the inline muffler-rather similar to a conventional car silencer -see below. This consists of a chamber with specialised internal piping through which the exhaust gas and water must flow. A good inline muffler should reduce exhaust noise by about 40%. The type of muffler offers some protection from back flow by virtue of its increased volume compared with the bare exhaust pipe, but is seldom sufficient on its own.

The best shape for an inline muffler is cylindrical. Oval versions can be easier to accommodate behind furniture and bulkheads while offering the same internal volume, but are more costly.
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Silencers