181–190 of 233 posts
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Hydrogen fuel cells are looking likely. Solar will probably produce too much electricity for usage during the day, so use that spare energy to split water to create Hydrogen fuel.
Isn't hydrogen difficult to store? I've heard that it will leak out of just about everything.
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I'm guessing that you're underestimating the cost of drag ... tailing a 300 sq meter "boat" would probably require more energy than it could produce. I have no data, and haven't done any back of the napkin calculations to back up my stance ... but just look at the speed difference between a monohull vs a catamaran vs a foil sailboat. Reducing the contact area with the water (and thus reducing drag) is _everything_.
Drag increases with the square of velocity [1]. Some of the ships might be able to travel much slower? I keep asking for sources because dismissals out of appeal to obviousness are so ubiquitous. [1] https://www.lmnoeng.com/Force/DragForce.php Edit: Admittedly, you may be right, but without even back-of-the-envelope calculations, and with the assumption that these boats must go as fast as possible, I don't know why.
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Sure, sorry. The rule-of-thumb max for solar irradiance is 1 kW/m^2 (noon, clear day, low latitude, etc): https://en.wikipedia.org/wiki/Solar_irradiance#Irradiance_on... The rule-of-thumb for the electric power output of a solar cell is about 20% of the irradiance. https://en.wikipedia.org/wiki/Solar_cell_efficiency And because this drops in the morning and evening and falls to zero at night, you realistically only g…
Thanks! My acceptance of the idea that drag might be manageable has to do with volume displacement and not surface area. A long shallow "tail" could exert orders of magnitude less drag (vis a vis surface area) than a deep heavy hull pushing up a big wake. (Related to why boats are long and narrow...) https://en.wikipedia.org/wiki/Wave-making_resistance Edit: The fact that you see that as a clear non-starter has me wa…
That's a lot. In contrast, the ship has an area of 24,000 m^2. A light-weight solar system might weigh 10 kg/m^2, so the whole thing weighs 20,000 tons. The ship has a staggering capacity of 200,000 tons.
So yes, it can carry it, but the 'long shallow tail' is really long - literally 20 miles, if it's the same 60m width as the ship - and really shallow. Maybe that's low drag, but if so, why wouldn't they build ships like that?
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This is a good question, and almost pure sail power may become a thing in the future. It looks like Maersk is trying to get ahead of the switch to cleaner fuel coming in 2020, which will increase their fuel costs by about 60%. This idea of putting sails on a large ship was at best only marginally cost-effective before now. Some practical considerations come into play - while saving money is good, being able to reach…
Why not use electrical propulsion and charge batteries from wind and solar? At first, as a fuel saving measure in optimal conditions (rely on internal combustion engines most of the time). Seems better than pure sail power, even though that is more efficient (due to direct wind to motion conversion).
Solar is just nowhere near good enough compared to the needs of a massive ship like this.
Wind would maybe work, but then remember that a turbine would effectively slow you down as you'd be pushing against the air.
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> Rotor ships take advantage of this same effect by spinning a large vertical cylinder, typically using an electric motor, and using the resulting force for propulsion. I always thought sails were partially defined by being passive. I wonder why these aren't called "rotor fans" if they're electrically driven? Is there anywhere it's discussed when rotors are expected to outperform normal fans? They seem to be used onl…
"Fan" implies the propulsion is in response to air being forced backwards. These rotors create lift in a forwards direction from the wind blowing across them, a bit like having a fixed wing pointing up.
Years ago on /. I saw a post about how wales bumps on the leading edges of their fins/flippers were to increase/modify the eddies around their fins in such a way as to provide them more thrust (or something, it's been years since I read the article) - and I was curious what it would look like to have helicopter blades with leading edge bumps on them similar to wales...
So, I'd like to see what dimples both convex and concave would have on the surfaces if these - like a golf ball.
Also, if you have never done it, take a cylindrical plastic cup and, in a bathtub full of water spin the cup as hard as you can on the surface of the water - like a top - and see how long you can get it to stand up. Kids like this trick.
I always thought it would be interesting to have a barge like flat boat on top of several cylindrical feet like floats, which can spin rapidly along the Z access and use it as thrust.
Viking Line installed similar 80-foot rotor sail on a LNG powered Cruise Ferry on the route between Helsinki-Stockholm. It reduces power usage roughly 20 percent (900 tonnes CO2 annually). Compared to tankers ferries don't carry significant amount of weight even when they are full. They are basically full of air and 60-100 cars or trucks. Together with using LNG, periodically cleaning the bottom of the ship, slower s…
> Viking Line installed similar 80-foot rotor sail on a LNG powered Cruise Ferry on the route between Helsinki-Stockholm. Turku - Stockholm, actually. > The best way to reduce energy consumption for a ship is to reduce the speed and make thinner ships. Do you mean thinner as in narrower, or thinner materials to save weight? If you mean narrower, I've understood bigger ships tend to have a length/width ratio of about…
reading:
https://gcaptain.com/cma-cgms-22000-teu-ships-to-feature-bul...
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And the ships. Drop an anchor and demand ransom to cut it free.
Even easier, just spoof the GPS signals with your own higher powered broadcast and make the ship think it's sailing around while it's actually stationary. Cant find the link but, some university actually demoed this working in real life with an actual container ship. Im imagining an LED throwie type big magnetic thing with gps RX and TX, and a satellite uplink. Cruise by the autonomous ship on a jetski near a port, t…
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I wonder: do sails alone generate enough power to move today's massive container ships? Or would the ships need to be smaller?
There's no question sails can move today's cargo volume. But the shape of the ships doesn't lend itself to sail power. I think these sails are specific to supporting other power. And the shape of today's ships is very much towards fitting more cargo. I think you'd need at least slightly bigger ships that are efficient for sail power alone, and able to carry similar cargo volume or mass.
This led me to wonder how important height was a restriction on ships. Turns out "air draft" is reported for major ports. Some interesting findings: The Panama Canal has an air draft of 201 ft imposed by the Bridge of the Americas; the Port of Oakland has an air draft of 220 ft imposed by the Golden Gate Bridge. Height from waterline does not appear to be typically listed for ships, but I would guess that most cargo…
I believe the unloaded freeboard of a typical containership is 80-100' The bridge (navigation deck) is higher, but the "sails" would be mounted from the deck, so I expect most ships would be OK.
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Thanks! My acceptance of the idea that drag might be manageable has to do with volume displacement and not surface area. A long shallow "tail" could exert orders of magnitude less drag (vis a vis surface area) than a deep heavy hull pushing up a big wake. (Related to why boats are long and narrow...) https://en.wikipedia.org/wiki/Wave-making_resistance Edit: The fact that you see that as a clear non-starter has me wa…
My assertion that it's a non-starter is based on the area of an 80 MW solar farm, not hydrodynamics. 80,000 kW x 24 hours / 1 kWh/m^2 = 2,000,000 square meters of solar cell area. That's a lot. In contrast, the ship has an area of 24,000 m^2. A light-weight solar system might weigh 10 kg/m^2, so the whole thing weighs 20,000 tons. The ship has a staggering capacity of 200,000 tons. So yes, it can carry it, but the 'l…
The application that no one will ever pay for might be a permanent, autonomous, very large, plastic garbage consuming vessel in the Pacific Gyre.
The form factor is less a limitation (in theory) than the will to allocate resources in such a way.