Chapter 2 N38143 Water lift systems For applications where the engine is installed below the water line, and in any installations where it is possible for water from the exhaust pipe to run back into the engine there are a number of solutions which can be considered. In sailing yachts and deep draught displacement boats it may be found that the engine exhaust outlet is near or below the waterline, a water lift exhaust system is then an option that may be considered. The main features of such a system are shown in (B). Pressure developed by the exhaust gases force a mixture of gas and water to a height which may be considerably above the engine.
When the engine is stopped the exhaust tank (B1) contains the water which falls back from the exhaust riser (B2). If a commercially available unit is used the manufacturers instructions should be carefully followed, but the key features are shown in (B). The exhaust muffler/water lift (B1) should have a minimum volume equal to 3 times the volume of the water that could be contained in the exhaust riser (B2). On sailing craft the muffler/water lift should be installed near the centre-line of the vessel. Particular care should be taken to prevent water from siphoning into the system and then flooding the engine.
There are two routes by which this could happen; from the exhaust outlet or by the sea water feed to the engine. The top of the exhaust riser (B3) should be a minimum of 450mm (18 inches) above the static water-line (B7), and the exhaust outlet (B4) should either be well above the static water level, or a siphon break should be fitted at (B5). The exhaust system may also become flooded by water entering through the sea water system on the engine, as the sea water pump impeller can not be relied upon to seal when stationary. To prevent such flooding the above system should be implemented. Page