Digging up my old naval architecture notes

Nice, thanks for going to the trouble.

It’s the speed that causes an exponential increase in required effective horsepower, not the displacement

Is any of this dependent on the size of the ship?

limited by how big you can effectively make your sails and all the wind turbulence issues that arise from that

Is this a bigger problem with big sails? I can imagine with a really big airfoil sail it might be hard to get the ideal angle / shape. But, if it’s a square-rigged ship it seems like it would be less sensitive to turbulence because it’s not an airfoil?

Sailing ships never went very fast, so that speed is never going to get much above 4-10 knots

And a modern cargo ship goes about 20 knots, right? But, does that mean that you could get maybe 16 knots out of the engine and 4 from the wind? Or is it that the wind can supply 1 MW of power, which is enough to move at 4 knots, but if you want to move at 20 knots you need 30 MW of power, so the wind would only supply about 3% of what you need, so it might not be worth it for all the added complexity?

Even goods that can survive a longer voyage will lose out on profit to those that get to the best market the quickest.

And, because petroleum-based fuel is very cheap because you don’t have to pay for the impact it causes, you can get an incredibly powerful engine that doesn’t cost an absurd amount to run. So, the additional cost to ship things at 30 knots using vast amounts of very dirty diesel is low enough that it’s still worth it?

You end up trying to sail upstream, essentially, as you outpace your wake

Yeah, I read about that, and how at one speed your bow and stern are both at wave peaks so it’s very efficient, but if you go faster your bow is a peak and your stern is a trough and that’s the worst situation.

If you wanted to go post-apocalypse mode though, is there any size-scaling thing related to ships that means that big ships are impossible to scale as sailing ships? Or if you can scale the sails up with the size of the ship, could you have an enormous post-Panamax sailing ship with absurd sized sails and a ridiculous sized keel that would cruise around at the same speed as the cargo sailing ships of old? Imagine seeing one of the biggest of the big cargo ships of today but rigged for sail power only. Either with a crew of 5000 post-apocalyptic refugees-turned-sailors handling the absurdly complex sails, or, with a computer in charge with hundreds of different motors all making continuous tiny adjustments to keep dozens of sails all set up perfectly.