4 ms·

Given the centuries of (mostly) effective use of sailing ships, maybe wind power would be the better candidate here?

by derefr 4y ago

atwood22 4y ago
Many ships already use wind power. I don't think you'd be able to harness the wind, convert it to electricity, and use the electricity more efficiently than a sail.
- derefr 4y ago
  Instantaneous efficiency is well and good, but a sail only redirects power; it doesn’t capture it. To me, the goal of adding wind power to a cargo ship would be the same as adding solar power: to recharge the batteries asynchronously to demand, to then later use that power when there is demand but no active supply. Wind→electric gives you the ability to “save up” power in a tailwind, and then later “spend” that power against a headwind. (You’d think pure wind power would do this as well—the engines can in theory work less hard if the sails are full—but wind is too precarious to match the slow ramp-up/ramp-down times of the giant motors used to power boat propellers. Those things are what power plant designers would call “base load” — mostly you don’t even turn them off, you just engage a giant clutch to put the boat into neutral when you don’t want to be moving. The master “transmission” of a boat is essentially a cylindrical steel flywheel; and you don’t want to lose its momentum. This is why boats a good match for bunker-fuel furnaces — or, on subs, nuclear — which are power sources that also ramp up/down slowly.)
jakeinspace 4y ago
Container ships with cargo must be like 50x the weight per unit of crosss-section compared to large wooden frigates. Way too lazy to do the math but I’m sure you’d need outrageously tall masts and sails to get any significant speed.
- landryraccoon 4y ago
  They could also redesign container ships to carry fewer containers. If automation can reduce the crew requirements and wind power can reduce the fuel consumption, a larger number of more efficient ships might be more viable than a small number of super transports.
  - sofixa 4y ago
    There would be other bottlenecks like shipping lanes and ports.
  - hnaccount_rng 4y ago
    I think you heavily overestimate the amount of crew on these ships. There are typically less than 20 people aboard any freighter. Which means that if you go down an order of magnitude the ships must run completely autonomously (at least part of the time). I think we are pretty much maxed out on automation
    - landryraccoon 4y ago
      > I think we are pretty much maxed out on automation That would be a very surprising result to me. I don't think we're maxed out on automation until the ships are loaded at the port, travel to their destination, then unloaded at the destination with no human labor. Unless you're telling me that robots load, unload, pilot and maintain the ships at sea, we aren't anywhere near maximum automation.
      - hnaccount_rng 4y ago
        I'm telling you that, unless you manage to _reliably_ automate _everything_, you need something like 6 personal to generate a permanent watch (probably more due to vacation/sickness/etc). This is kind of the minimal requirement for having any redundancy for unforeseen situations _at all_. And it is only a factor of 3 below the current crewing levels. Which gives you a factor of 3 more ships. Unless you are willing to risk loosing the ship due to a 1-in-1000 event which your automation did not take into account, then this is your limit. And ships are expensive, even compared to officer salaries. And those generate most of the crewing costs anyways. So if you have to pay 6 officers, adding 2-3 for the engine to require less dock-time and 12 ratings really doesn't push up your costs that much (especially not compared to the capital cost). But you get a lot of redundancy. So yeah, I would say most of the economically viable automation has been done But this has been a surprisingly interesting rabbit hole, thanks for that. There are different numbers for ships around starting with 50k [0] on the low end and the high end is 100k [1] being operated by between 1.5m [2] and 1.9m [3] personell. At the outer edge this would give 40 people per ship. Whereas reports put the number more at 20-25 [4]. The last one also mentions that there are requirements, by law, which typically require something like 6 people (often with nationality requirements) to be on board. All sources e.g. [0] https://www.statista.com/statistics/264024/number-of-merchant-ships-worldwide-by-type/ https://www.statista.com/statistics/264024/number-of-merchan... [1] https://hbs.unctad.org/merchant-fleet/ https://hbs.unctad.org/merchant-fleet/ [2] https://www.ics-shipping.org/shipping-fact/shipping-and-world-trade-global-supply-and-demand-for-seafarers/ https://www.ics-shipping.org/shipping-fact/shipping-and-worl... [3] https://www.ics-shipping.org/press-release/russian-and-ukrainian-seafarers-make-up-14-5-of-global-shipping-workforce-according-to-ics/ https://www.ics-shipping.org/press-release/russian-and-ukrai... [4] https://www2.deloitte.com/content/dam/Deloitte/global/Documents/dttl-er-challengeindustry-08072013.pdf https://www2.deloitte.com/content/dam/Deloitte/global/Docume...
- Schroedingersat 4y ago
  Kites and cylindrical sails are worth the cost and logistical difficulties as a suppliment in some niches, but are not enough on their own.
- derefr 4y ago
  Who said anything about sails? I meant wind turbines powering the engines.
  - jakeinspace 4y ago
    Well, if the wind is at your back, I think it’d just be more efficient to use sails, since it skips conversion losses. If it’s a headwind, well you’re just adding drag. You can’t put wind turbines on a vehicle and come out ahead of sails.
    - derefr 4y ago
      This presumes there’s any advantage in a ship arriving early. Usually an early ship is just as bad as a late ship — their booked port slot isn’t until hours/days later. So, in a tailwind, you don’t want to actually go faster; you want to keep a constant speed, but just use less power doing so. And direct wind capture via sails is (AFAIK) unpredictable enough that you can’t keep a constant speed when relying on it. (Are there robotic sail-trimmer control systems designed to always take an exact amount of impulse from the wind and discard any excess?) Sticking a wind turbine on your boat, on the other hand, is basically regenerative braking. You turn the excess speed you don’t want/need at the time, into stored power for later when you do need it, to exactly the degree to leave you with the speed you want. A tailwind is to a boat as “going downhill” is to a car.
      - landryraccoon 4y ago
        If the ship arrives early, can't it just sit a few miles from port and wait in the ocean? The ship must have been provisioned to remain at sea for that time anyway if it was expecting to arrive later.
- fulafel 4y ago
  Even the current small retrofitted rotor sails are effective in cutting fuel use, so why not. https://maersktankers.com/newsroom/norsepower-rotor-sails-confirmed-savings https://maersktankers.com/newsroom/norsepower-rotor-sails-co...
zdragnar 4y ago
This raises a few questions in my mind: 1- Do shipping lanes still stick to prevailing winds, or are more direct routes significantly faster? 2- Would becalmed seas or being blown off course by a storm be a big enough risk that ships would still need a full compliment of fuel, or close enough as to make the maintenance costs of both engine and sails, weight and other factors override the benefit? 3- Does the addition of sails increase the risk of rolling or swaying stresses on the ship? I imagine this might require some extensive structural changes or upgrades to ships, with no idea of what the cost would be compared to a different kind of retrofit (i.e. continuing to use propellers but with a different fuel source).
jon_adler 4y ago
Sail assisted cargo ships are under active development as a method for reducing energy consumption.

Given the centuries of (mostly) effective use of sailing ships, maybe wind power would be the better candidate here?

by derefr 4y ago

Given the centuries of (mostly) effective use of sailing ships, maybe wind power would be the better candidate here?

Many ships already use wind power. I don't think you'd be able to harness the wind, convert it to electricity, and use the electricity more efficiently than a sail.

derefr 4y ago
Instantaneous efficiency is well and good, but a sail only redirects power; it doesn’t capture it. To me, the goal of adding wind power to a cargo ship would be the same as adding solar power: to recharge the batteries asynchronously to demand, to then later use that power when there is demand but no active supply. Wind→electric gives you the ability to “save up” power in a tailwind, and then later “spend” that power against a headwind. (You’d think pure wind power would do this as well—the engines can in theory work less hard if the sails are full—but wind is too precarious to match the slow ramp-up/ramp-down times of the giant motors used to power boat propellers. Those things are what power plant designers would call “base load” — mostly you don’t even turn them off, you just engage a giant clutch to put the boat into neutral when you don’t want to be moving. The master “transmission” of a boat is essentially a cylindrical steel flywheel; and you don’t want to lose its momentum. This is why boats a good match for bunker-fuel furnaces — or, on subs, nuclear — which are power sources that also ramp up/down slowly.)

jakeinspace 4y ago

Container ships with cargo must be like 50x the weight per unit of crosss-section compared to large wooden frigates. Way too lazy to do the math but I’m sure you’d need outrageously tall masts and sails to get any significant speed.

landryraccoon 4y ago
They could also redesign container ships to carry fewer containers. If automation can reduce the crew requirements and wind power can reduce the fuel consumption, a larger number of more efficient ships might be more viable than a small number of super transports.
- sofixa 4y ago
  There would be other bottlenecks like shipping lanes and ports.
- hnaccount_rng 4y ago
  I think you heavily overestimate the amount of crew on these ships. There are typically less than 20 people aboard any freighter. Which means that if you go down an order of magnitude the ships must run completely autonomously (at least part of the time). I think we are pretty much maxed out on automation
  - landryraccoon 4y ago
    > I think we are pretty much maxed out on automation That would be a very surprising result to me. I don't think we're maxed out on automation until the ships are loaded at the port, travel to their destination, then unloaded at the destination with no human labor. Unless you're telling me that robots load, unload, pilot and maintain the ships at sea, we aren't anywhere near maximum automation.
    - hnaccount_rng 4y ago
      I'm telling you that, unless you manage to _reliably_ automate _everything_, you need something like 6 personal to generate a permanent watch (probably more due to vacation/sickness/etc). This is kind of the minimal requirement for having any redundancy for unforeseen situations _at all_. And it is only a factor of 3 below the current crewing levels. Which gives you a factor of 3 more ships. Unless you are willing to risk loosing the ship due to a 1-in-1000 event which your automation did not take into account, then this is your limit. And ships are expensive, even compared to officer salaries. And those generate most of the crewing costs anyways. So if you have to pay 6 officers, adding 2-3 for the engine to require less dock-time and 12 ratings really doesn't push up your costs that much (especially not compared to the capital cost). But you get a lot of redundancy. So yeah, I would say most of the economically viable automation has been done But this has been a surprisingly interesting rabbit hole, thanks for that. There are different numbers for ships around starting with 50k [0] on the low end and the high end is 100k [1] being operated by between 1.5m [2] and 1.9m [3] personell. At the outer edge this would give 40 people per ship. Whereas reports put the number more at 20-25 [4]. The last one also mentions that there are requirements, by law, which typically require something like 6 people (often with nationality requirements) to be on board. All sources e.g. [0] https://www.statista.com/statistics/264024/number-of-merchant-ships-worldwide-by-type/ https://www.statista.com/statistics/264024/number-of-merchan... [1] https://hbs.unctad.org/merchant-fleet/ https://hbs.unctad.org/merchant-fleet/ [2] https://www.ics-shipping.org/shipping-fact/shipping-and-world-trade-global-supply-and-demand-for-seafarers/ https://www.ics-shipping.org/shipping-fact/shipping-and-worl... [3] https://www.ics-shipping.org/press-release/russian-and-ukrainian-seafarers-make-up-14-5-of-global-shipping-workforce-according-to-ics/ https://www.ics-shipping.org/press-release/russian-and-ukrai... [4] https://www2.deloitte.com/content/dam/Deloitte/global/Documents/dttl-er-challengeindustry-08072013.pdf https://www2.deloitte.com/content/dam/Deloitte/global/Docume...
Schroedingersat 4y ago
Kites and cylindrical sails are worth the cost and logistical difficulties as a suppliment in some niches, but are not enough on their own.
derefr 4y ago
Who said anything about sails? I meant wind turbines powering the engines.
- jakeinspace 4y ago
  Well, if the wind is at your back, I think it’d just be more efficient to use sails, since it skips conversion losses. If it’s a headwind, well you’re just adding drag. You can’t put wind turbines on a vehicle and come out ahead of sails.
  - derefr 4y ago
    This presumes there’s any advantage in a ship arriving early. Usually an early ship is just as bad as a late ship — their booked port slot isn’t until hours/days later. So, in a tailwind, you don’t want to actually go faster; you want to keep a constant speed, but just use less power doing so. And direct wind capture via sails is (AFAIK) unpredictable enough that you can’t keep a constant speed when relying on it. (Are there robotic sail-trimmer control systems designed to always take an exact amount of impulse from the wind and discard any excess?) Sticking a wind turbine on your boat, on the other hand, is basically regenerative braking. You turn the excess speed you don’t want/need at the time, into stored power for later when you do need it, to exactly the degree to leave you with the speed you want. A tailwind is to a boat as “going downhill” is to a car.
    - landryraccoon 4y ago
      If the ship arrives early, can't it just sit a few miles from port and wait in the ocean? The ship must have been provisioned to remain at sea for that time anyway if it was expecting to arrive later.
fulafel 4y ago
Even the current small retrofitted rotor sails are effective in cutting fuel use, so why not. https://maersktankers.com/newsroom/norsepower-rotor-sails-confirmed-savings https://maersktankers.com/newsroom/norsepower-rotor-sails-co...

zdragnar 4y ago

This raises a few questions in my mind: 1- Do shipping lanes still stick to prevailing winds, or are more direct routes significantly faster? 2- Would becalmed seas or being blown off course by a storm be a big enough risk that ships would still need a full compliment of fuel, or close enough as to make the maintenance costs of both engine and sails, weight and other factors override the benefit? 3- Does the addition of sails increase the risk of rolling or swaying stresses on the ship? I imagine this might require some extensive structural changes or upgrades to ships, with no idea of what the cost would be compared to a different kind of retrofit (i.e. continuing to use propellers but with a different fuel source).

jon_adler 4y ago

Sail assisted cargo ships are under active development as a method for reducing energy consumption.