47 MLB Raw Water Cooling System

Question 1

What are the 5 functions of the primary raw water system?

Answer 1

• Maintains fuel oil temperatures below 90°F.
• Removes heat from engine coolant to maintain proper operating temperatures.
• Removes heat from reduction gear lube oil to maintain proper operating temperatures.
• Removes heat from the steering system hydraulic oil to maintain proper operating temperatures.
• Provides cooling and quieting for engine exhaust.

Question 2

Describe the locations of the raw water valves.

Answer 2

Each raw water valve is located on the opposite side of the keel of the engine that it services between Frames 4 and 5 below the engine room ladder.

Question 3

Raw Water System Flow

Answer 3

• Step 1: The raw water flows through a 4” duplex strainer on the port and starboard inboard girders between Frames 4 and 5.
• Step 2: From the sea strainer, water flows to the raw water pump that has a flow rating of 67 GPM.
• Step 3: From the raw water pump, water flows through the fuel cooler and maintains fuel temperature below 90°F.
• Step 4: From the fuel cooler, water is piped to the engine heat exchanger where it cools the engine coolant.
• Step 5: On the outboard side of each engine, the flow is divided. One direction leads forward through Bulkhead 5 to the reduction gear oil cooler and the shaft seal for sealing and cooling. The second flow is restricted through a 1” restrictor plate and goes to the water-cooled muffler. On the starboard side, a separate branch provides cooling for the steering system hydraulic fluid.
• Step 6: After passing through the reduction gear oil cooler, the flow reenters the engine room and branches off. One leg goes to the deicing valve, while the other discharges overboard through the water-cooled muffler.
• Step 7: In the water-cooled muffler, raw water cools and quiets the exhaust and is discharged over the side via the exhaust ports. The mufflers are cross-connected to prevent back pressure if one exhaust port is submerged. An isolation valve is installed in the cross-connect to prevent internal condensation in the event of single engine operation.