While steaming at 13.5 knots, your vessel consumes 251 barrels of fuel oil per day. In order to reduce consumption to 129 barrels of fuel oil per day, what is the maximum speed the vessel can turn for?
• Relationship between speed and fuel consumption for displacement vessels (think about how power changes with speed) • How to use ratios and exponents to compare fuel use at two different speeds • Converting barrels per day into a usable ratio without changing units
• Ask yourself: if fuel consumption is proportional to some power of the speed, how can you set up a proportion between the known condition and the new condition? • How can you rearrange the proportion to solve for the new speed, given the new (lower) fuel consumption? • Once you compute the new speed, which multiple-choice option is closest to your result?
• Be sure you are using the same time unit (per day) in both conditions so they cancel properly • Double-check that you raise the speed ratio to the correct power used for this type of exam question (often related to shaft horsepower vs. speed). • Verify that your final speed is less than 13.5 knots, since fuel consumption is going down.
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