As indicated in the graph, what percentage of rated horsepower is being developed when operating the main propulsion turbine at 80% speed? See illustration SE-0018.
• Relationship between percent speed and percent horsepower for a propulsion turbine/propeller • How to read a curve graph: go up from the x‑axis value, then across to the y‑axis • Typical propeller law idea: power changes much faster than speed
• On the x‑axis, locate 80% speed. From that point, what direction along the graph do you move first, and then second, to find the corresponding horsepower? • Visually compare the point at 80% speed to the labeled horsepower grid lines: is it closer to 20%, 50%, or 80% horsepower? • Think about this: if you cut speed to 50%, does horsepower usually drop to 50%, much less than 50%, or more than 50%? Use that same idea at 80% speed.
• Be sure you are reading speed on the horizontal axis and horsepower on the vertical axis • At 80% speed, carefully note which two horizontal grid lines the curve lies between and roughly how far between them • Confirm that your chosen option’s horsepower percentage matches the visual position of the curve at 80% speed (don’t just average or guess)
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