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> To be in motion, any object must need to overcome friction. For large container ships, between 2 and 10% of resistance encountered is caused by drag, which worsens a vessel's fuel economy as the additional friction requires more energy (in the form of fuel) to overcome.

Do they mean aerodynamic drag here? Otherwise, what’s the remaining 90 to 98% of resistance from, if not drag?

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I imagine hydrodynamic drag (and engine inefficiencies after that). Water is a thousand times more dense and about 50 times more viscous than air.

I'm surprised this isn't already "a thing" though, as the interaction of wind and waves have been known about for centuries and clearly a big blocky ship is going to be very much not finessed aerodynamically. The hydrodynamic Reynolds number is very large and I suspect dominated design considerations of efficiency with a limited time (and computational) budget.

Right, but hydrodynamic drag is drag too.

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