Engineering · Cooling — Jacket Water
Most medium/large marine diesels use a closed fresh-water jacket cooling system cooled by seawater in a heat exchanger rather than raw seawater directly in the jacket because:
- ASeawater is a better lubricant
- BIt eliminates the need for a thermostat
- CFresh water boils at a lower temperature
- DTreated fresh water avoids scale, corrosion, and the thermal shock that raw seawater would cause in the engine✓ Correct
Explanation
Circulating treated fresh water through the jacket (and cooling that water with seawater in a separate exchanger) prevents salt scaling and corrosion of engine passages and allows higher, controlled jacket temperatures via a thermostat.
Authority: Modern Marine Engineer's Manual; cooling systems
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