While steaming at 14.5 knots, your vessel consumes 242 barrels of fuel oil per day. In order to reduce consumption to 152 barrels of fuel oil per day, what is the maximum speed the vessel can turn for?
• Relationship between fuel consumption and speed for displacement vessels (approximately proportional to the cube of speed) • Setting up a ratio/proportion between the two operating conditions (original vs reduced consumption) • Solving for the unknown speed after reducing fuel consumption
• How can you express the relationship between fuel consumption and speed using an equation (hint: think of speed raised to a power)? • If you take the ratio of the new fuel consumption to the old fuel consumption, how does that relate to the ratio of the new speed to the old speed? • Once you solve for the new speed using the ratio, which of the options is closest to your calculated value?
• Make sure you use consistent units (knots for speed, barrels per day for fuel) and keep them the same on both sides of the ratio • Confirm that your assumed power relationship (e.g., speed squared, speed cubed, etc.) matches what is typically used for displacement hull fuel calculations • After calculating the new speed, re-check by cubing (or using your chosen power) it to see if it produces a fuel consumption close to 152 barrels/day when compared with the original condition
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