It's even worse than that, for a drag force proportional to the square of the speed, the power is proportional to the cube of the speed. As for the transatlanti

It's even worse than that, for a drag force proportional to the square of the speed, the power is proportional to the cube of the speed. As for the transatlantic voyage in 12 days vs 8 or 6 I don't know on what they based it. Maybe ships don't always go at the nominal speed as it may not be economical to do so. 8 days is 15-16 knots, so this corresponds to a more economical slow steamer. As they pitch an environmentally friendlier solution, a comparison to the next best thing (slow steaming) may be more apt. Using the cube-law, ~2/3 the speed ~= 0.3 the power. And only 1/8 if you compare 10 to 20!