While steaming at 19.5 knots, your vessel burns 297 bbls of fuel per day. What will be the rate of fuel consumption if you decrease speed to 15 knots?
• Fuel consumption and speed-power relationship (fuel use roughly proportional to the cube of speed for displacement hulls in many exam problems) • How to set up a ratio or proportion between old speed/consumption and new speed/consumption • Converting "per day" consumption into a rate that can be scaled by speed change
• How does fuel consumption typically change when you reduce speed on a displacement vessel: does it drop a little, by half, or more than that? • If fuel use is related to the cube of speed, what happens to fuel consumption when speed goes from 19.5 knots to 15 knots? Write this as a fraction. • Once you find the fraction for the change in power/fuel, how do you apply that fraction to the original 297 bbl/day to get the new daily consumption?
• Compute the speed ratio (new speed / old speed) carefully before cubing it. • Make sure you multiply the original 297 bbl/day by the correct dimensionless factor (no unit mistakes). • After calculating, compare with the answer choices and see if the result is significantly less than 297 but still reasonable for a modest speed reduction.
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