That's not really accurate. Displavement hulls are more efficient at lower speeds for the same displacement (i.e. payload mass), but at higher speeds, the speed-power relationship of planing hulls flattens allowing for MUCH higher speed transits, whereas the power requirements for displacement hulls just continues to skyrocket with increased speeds (1).

Freighters are generally displacement hulls because they carry thousands of tonnes of cargo. This sizable displacement would make it impractical for these vessels to "get up on plane" (assuming their hulls were shaped like planing hulls vice displacement hulls). You can simply carry more payload in a displacement hull than a planing hull. Planing hulls like to be lightweight. It's not impossible to make a planing freighter, just impractical - and all of that inertia and mechanical stress on the hull structure while traveling at high speeds would be very difficult to design against, not to mention very difficult/unsafe to amneuver in a sea lane or inclement weather. There are certainly high speed ferries, which are generally catamarans (for added stability) with similar speed-power characteristics to planing hulls, but those are still carrying relatively lighter cargo (humans, some cars) over shorter distances compared to fairly dense bulk liquid/material/container cargo transiting accross oceans.

1. https://images.app.goo.gl/Yn3znGUBgiM9jkB4A

> Displacement hulls are more efficient at lower speeds for the same displacement

Yes. I thought it was obvious I was comparing at displacement speeds only; I'm sorry for not being more clear.

And, actually, the speed doesn't matter, because the fuel usage of planing hull makes it uneconomic at any speed, even if such speed is greater than displacement hull speed, even though it's infinitely more effective than a displacement hull at those speeds (since a displacement hull cannot reach those speeds basically by definition).

I think you could argue an airliner is just an extreme form of planing hull - certainly a seaplane is. And those are used for high-value freight.

And, a planing hull is not a great shape for displacement. I think they have significantly more drag, just 2x or 3x though, when operating at displacement speeds.

If anyone's confused about 10x in the GP post and 2-3x in this one, a given size boat with a displacement hull might have a hull speed of 6 kts and with a planing hull a hull speed of 5 kts.

At 2 kts, they'd both probably be in displacement, but the planing hull would be using 2-3x power.

At 6 kts, the planing hull would be using about 10x power, because it would be operating in planing mode while the displacement hull is still operating in the very efficient displacement mode.

Only the planing hull could exceed 6 kts.