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The exhaust system back pressure must not exceed 10.2 kPa (40 inch of H2O) when measured within 305 mm (12 inch) of the exhaust outlet from the engine. This includes wet exhaust systems, dry exhaust systems, part dry part wet exhaust systems, and water lift exhaust systems. It is important that the exhaust system is designed so that water does not enter the engine under any condition. Serious engine damage can occur. |
Wet Exhaust System
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| Illustration 1 | g00745325 |
Typical wet exhaust system installation (1) 5 degree minimum average slope (2) Exhaust piping (3) Silicone rubber bellows (4) Centerline of the crankshaft (5) The point of water injection should be a minimum of 200 mm (8 inch) above the level of the sea water. (6) Level of the sea water | |
Wet exhaust systems are the most common type of exhaust system for small vessels. Wet exhaust systems use the sea water that is used for the cooling system. The sea water is injected into the exhaust piping in order to cool the exhaust gases. The sea water and the exhaust gases are then exited from the vessel. Rubber exhaust hose may be used. This is due to low surface temperature.
Illustration 1 represents a typical installation of a wet exhaust system. In most cases, the exhaust outlet will exit just above the level of the sea water. A minimum of 5 degrees slope is required. The point of water injection must be at least 200 mm (8 inch) above the level of the sea water. The actual height will depend on the type of service.
The diameter of the exhaust piping (2) will depend on the engine arrangement. Refer to Table for the required sizes of the exhaust piping.
| Required Bore for the Exhaust Piping | |
| Engine Model | Bore |
| Naturally Aspirated 3054B Marine engine | 76.0 mm (3.00 inch) |
| Turbocharged 3054 Marine engine | 90.0 mm (3.50 inch) |
| Naturally Aspirated 3056 Marine engine | 76.0 mm (3.00 inch) |
| Turbocharged Aftercooled 3056 Marine engine | 125.0 mm (5.00 inch) |
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| Illustration 2 | g00745344 |
Typical arrangement for an exhaust bellows joint with a double hump (7) When there is restricted space, use an exhaust bellows joint with a double hump. (8) Engine (9) Marine transmission | |
Consideration must be given to flexibility in the exhaust piping. This is true especially if the engine is mounted with flexible engine mounts. If the exhaust piping must pass through a bulkhead that is immediately behind the engine, an exhaust bellows joint with a double hump should be installed. This will provide flexibility. The exhaust bellows joint should not be compressed after final installation.
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| Illustration 3 | g00745326 |
Typical arrangement (10) Water injection elbow (11) Insulating blanket (12) Direction of possible rotation for the specific installation (13) Dry elbow | |
Use the system that is shown in Illustration 3 in order to achieve sufficient height above the level of the sea water. The two 90 degree elbows can be rotated in order to fit the specific installation.
Dry Exhaust System
A dry exhaust system for a marine installation needs to be designed carefully. Enclosing exhaust components that are high temperature in an enclosed space should be minimized.
The dry exhaust system should include a flexible connection. An exhaust bellows joint that is made of stainless steel is suitable for a flexible connection. A flexible connection is required to accommodate movements that do not involve twisting. There should be no load on the exhaust bellows joint. The exhaust bellows joint will absorb the expansion and the movement of the engine. Insulate the rest of the exhaust system.
A condensate drain may be necessary if there is a long run of exhaust piping. Drain outside of the vessel.
The diameter of the exhaust piping for a dry exhaust system depends on the engine arrangement. Turbocharged engines require a 76 mm (3 inch) bore. Naturally aspirated engines require a 63 mm (2.5 inch) bore.
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| Illustration 4 | g00786398 |
Typical arrangement for the naturally aspirated 3054B Marine engine (1) The exhaust system is allowed to move because of the bracket with the link. (2) Insulating lagging (3) The bracket that is rigid should be able to support the weight of the exhaust system. (4) Flange (5) Insulating blanket (6) Stainless steel bellows (7) Insulating blanket (8) 45 degree elbow (9) 90 degree elbow (10) Insulating blanket | |
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| Illustration 5 | g00786396 |
Typical arrangement for the turbocharged 3054 Marine engine (11) The exhaust system is allowed to move because of the bracket with the link. (12) Insulating lagging (13) The bracket that is rigid should be able to support the weight of the exhaust system. (14) Flange (15) Insulating blanket (16) Stainless steel bellows (17) Insulating blanket (18) 90 degree elbow (19) 90 degree elbow (20) Insulating blanket | |
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| Illustration 6 | g00786498 |
Typical arrangement for the naturally aspirated 3056 Marine engine (21) The exhaust system is allowed to move because of the bracket with the link. (22) Insulating lagging (23) The bracket that is rigid should be able to support the weight of the exhaust system. (24) Flange (25) Insulating blanket (26) Stainless steel bellows (27) Insulating blanket (28) Adapter for the exhaust manifold (29) 90 degree elbow (30) Insulating blanket | |
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| Illustration 7 | g00786497 |
Typical arrangement for the turbocharged aftercooled 3056 Marine engine (31) The exhaust system is allowed to move because of the bracket with the link. (32) Insulating lagging (33) The bracket that is rigid should be able to support the weight of the exhaust system. (34) Flange (35) Insulating blanket (36) Stainless steel bellows (37) Insulating blanket (38) 90 degree elbow (39) Insulating blanket | |
Part Wet, Part Dry Exhaust System
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| Illustration 8 | g00745333 |
Typical arrangement (1) 5 degree minimum fall (2) The point of water injection should be a minimum of 200 mm (8 inch) above the level of the sea water. (3) Level of the sea water (4) Flexible hanger (5) Exhaust extension (6) Stainless steel bellows | |
If the engine is mounted well below the level of the sea water (3), then the advantages of a wet exhaust system can still be gained. However, the water injection must take place at a point sufficiently above the level of the sea water.
Refer to Illustration 8 for a typical arrangement of a part wet, part dry exhaust system. The modular exhaust components allow different arrangements. The part wet, part dry exhaust system can be used on turbocharged engines and on naturally aspirated engines. Refer to Table 1 for the required bore for the exhaust piping.
Water Lift Exhaust System
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| Illustration 9 | g00745335 |
Typical arrangement (1) The top of the exhaust riser must be above the level of the sea water. The connection for the siphon break to the exhaust pipe must be above the level of the sea water. The minimum distance is 450 mm (17.72 inch). (2) 12.7 mm (0.50 inch) bore for the siphon break (3) Overboard outlet (4) Water injection elbow (5) Exhaust riser (6) Exhaust tank | |
The dry exhaust system or the part dry, part wet exhaust system should be considered when the engine is mounted at the level of the sea water or below the level of the sea water. If neither systems are suitable, then a water lift exhaust system may be required. However, a water lift exhaust system will make starting the engine more difficult.
Refer to Illustration 9 for the features of the water lift exhaust system. The pressure that is developed by the exhaust gases will force a mixture of gas and water to a height which may be above the engine. The water from the exhaust riser falls back into the exhaust tank when the engine is stopped.
The system must meet the requirements for exhaust back pressure. The back pressure must not be greater than 10.2 kPa (40 inch of H2O). The back pressure must be measured within 305 mm (12 inch) of the turbocharger outlet or the exhaust outlet. The minimum volume of the exhaust tank should be 3 times the volume of the water in the exhaust riser. The exhaust tank should be installed near the centerline of the vessel.
Note: If a proprietary unit is installed, then follow the instructions from the OEM for installation.