A ballast pump with a capacity of 200 gpm (757 lpm) is used to fill a ballast tank with seawater. If the pump discharges seawater into the tank for one hour, how many tons of saltwater ballast have been taken onboard?
• Pump capacity and time – how many gallons are pumped in one hour at 200 gpm? • Volume conversions – relationship between gallons and cubic feet (think 7.48 gal ≈ 1 ft³). • Saltwater weight per unit volume – about how many pounds (or cubic feet) of seawater make one long ton of displacement?
• First, find the total volume pumped in gallons over one hour, then convert that to cubic feet. • Next, use an approximate weight (or volume) of seawater per long ton to convert from cubic feet of seawater to tons. • Compare your calculated tons (in long tons) with the choices and see which one is the closest match.
• Be sure you’re using 60 minutes in one hour when finding total gallons pumped. • Use the correct gallons-to-cubic-feet conversion (about 7.48 gallons per cubic foot). • Use a seawater long-ton conversion, such as about 35 cubic feet per long ton, or its equivalent in pounds, and keep units consistent.
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