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Comment by sethbannon | Hacker News Reader

There's a YC company that's building hydrofoil container ships to lower the GHG emissions from shipping.

https://www.boundarylayer.tech/

Interesting, and the video is informative (though a bit short) but we always want to know the caveats

- Why hasn't this been built before? Yes, minor hydrofoil ships have been built but why not cargo ones? (Constructor conservatism? Some issues that others have run into? Lack of technology before that)

- How does this fare in a marine thunderstorm?

- How many customers are time sensitive (but not much) so as to fit their window?

- What kind of problems can going 4x the speed on an open ocean can create?

- Is the actual cost 4x less once you factor everything in?

My bet is that this makes sense for shorter routes (like multiple ferry routes in Europe), maaaybe for "shorter" cargo routes, not so sure for the longer routes (though China-LA is not "too long")

Fairly large hydrofoil ships have been built before so it will probably work from an engineering standpoint. But the economics are questionable. They're betting on finding customers who want a middle option between slow, cheap container ships and fast, expensive air freight. I'm skeptical that many such customers exist.

Hydrofoils obviously can't operate safely in heavy sea states. When a storm comes up they'll have to delay sailing, or route around. That will add some unpredictability to delivery schedules.

There's a lot of vaporware out there, but this foiling ferry has been paid for by the City of Stockholm and will launch next year:

https://candelaspeedboat.com/public-transport/

> Yes, minor hydrofoil ships have been built but why not cargo ones?

I'm assuming that the additional of the weight of the cargo means that you would need to go much faster in order to lift the ship up on the hydrofoils, and this makes it infeasable.

Also you need to lift your fuel and you might get into a rocket equation type problem. Fuel is less dense than water so one might imagine it contributes a little to buoyancy but aloft, you're paying to lift it along with the cargo.

Fuel means range so that all might get back to the mission: ferry or transoceanic.

Airplanes also have to lift their own fuel, yet are not, in practice, hostage to the rocket equation (though early, grossly inefficient jets may have experienced something like it.) Three things that make the rocket equation a problem for orbital launches are, firstly, you have to take along the oxidizer as well; secondly, you have to do much more lifting (and, considerably more significantlty, accelerating) than an airplane; and thirdly, without dynamic lift, all the lifting and accelerating has to be done directly by engine thrust.

Also, while fuel oil is buoyant, it still has mass and weight, and the fuel in a ship contributes its own weight's worth of displacement. Displacement, in turn, causes wave resistance.

The larger a ship gets, the less significant, proportionally, both wave and friction drag become, reducing the incentive for foiling. It seems significant that the YC company mentioned elsewhere in these comments (Boundary Layer Technologies) positions itself as competing with air freight rather than shipping (and, as flying in the thin air of the tropopause is pretty efficient compared with generating lift in water, I would guess part of their calculation involves building much larger-capacity vessels than current and projected air freighters.)

Hadn't seen those, really interesting, thanks!

Also can't help smiling at their use of "BLT" as an abbreviation for the company name, I guess we know what their Official Company Lunch is going to be [1]. :)

I wonder if there has been any progress, the site is kind of ... light on the details. The prototype single-container ship was cute, though.

[1]: https://en.wikipedia.org/wiki/BLT

Check out our foiling ferry P-30 that already is paid for by the city of Stockholm and will be launched Q4 2022:

https://candelaspeedboat.com/public-transport/

It is interesting that the illustrations use traditional looking props rather than ducted or shaft-less rim-driven thrusters.

https://www.researchgate.net/project/RIM-DRIVEN-THRUSTER

A similar company: https://freightfish.io/

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