While steaming at 15 knots, your vessel burns 326 bbls of fuel per day. What will be the rate of fuel consumption if you decrease speed to 12.2 knots?
• Relationship between speed and fuel consumption (fuel usually changes with roughly the cube of speed for displacement hulls) • Set up a proportion or power relationship between the two speeds (15 knots and 12.2 knots) • Careful unit consistency: keep fuel in bbl/day and speed in knots
• How does fuel consumption typically change when speed is reduced on a displacement vessel: directly with speed, with speed squared, or with speed cubed? • If you know the fuel burn at 15 knots, how can you scale that to find the burn at 12.2 knots using the same speed–fuel relationship? • Once you compute the new theoretical burn, which option is closest to your calculated value?
• Be sure you apply the same relationship (e.g., proportional to speed³) to both speeds, not just linearly • Double-check your exponent and calculator steps; a small mistake in the power will give a very different answer • After calculating, verify that the new fuel rate is lower than 326 bbl/day but still reasonable for only a small reduction in speed
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