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Comment by hedora | Hacker News Reader

I was wondering about usng solar panels to offset batteries. These ships travel at 43 kph. A 5000 km range ship needs 6.5 GWh of storage for a roughly 100 hour trip, or 33 hours of near-peak solar production (assuming no clouds). So, it would need about 200 megawatts of solar to completely avoid charging while docked. 20 watt/sqft is pretty good these dats, so it would need 10M sq ft of solar panels on its deck. Cargo ship decks max out at about 265K sqft.

So, there's no point in putting a solar array on the deck of one of these things.

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These huge ships should be nuclear powered like navy ships.

Yeah, put 100kg of high grade uranium or plutonium on a ship with 30 crew and sail it past somalia. Great plan. I mean assuming it gets there and doesn't melt down and contaminate an entire sea because of how well known the shipping industry is for not cutting corners. It'll also definitely not result in nuclear waste getting dumped wherever.

I mean there's at least a chance that the nuclear reactor which costs 10x as much as the proposed electric ship will get stolen wholesale and used for civilian purposes, so that could be an upside.

You don't need to enrich the fuel and you definitely don't need plutonium.

I'm not saying it's all, ahem, plain sailing, but that part at least isn't a necessary risk.

Time to bring back the merchant marine

I wonder if building nuclear ships that float in international water could sidestep some of the NIMBY-ism for nuclear power. I think some company might have already pursued that approach.

There has been a couple of attempts. https://en.wikipedia.org/wiki/Nuclear_marine_propulsion#Merc...

So far it hasn't really been economically feasible unlike icebreakers. Russia is the only one who is operating those.

Yeah, but it have his problems... mainly that nobody likes to allow to dock it : https://en.wikipedia.org/wiki/NS_Savannah

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.

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.)

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.

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.

There would be other bottlenecks like shipping lanes and ports.

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

> 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.

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-merchan... [1] https://hbs.unctad.org/merchant-fleet/ [2] https://www.ics-shipping.org/shipping-fact/shipping-and-worl... [3] https://www.ics-shipping.org/press-release/russian-and-ukrai... [4] https://www2.deloitte.com/content/dam/Deloitte/global/Docume...

Kites and cylindrical sails are worth the cost and logistical difficulties as a suppliment in some niches, but are not enough on their own.

Who said anything about sails? I meant wind turbines powering the engines.

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.

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.

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.

Even the current small retrofitted rotor sails are effective in cutting fuel use, so why not.

https://maersktankers.com/newsroom/norsepower-rotor-sails-co...

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).

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

And container ships don't really have anything you could call a deck in this context.

Container ships don't, but eg. oil tankers do.

https://www.istockphoto.com/video/oil-tanker-floating-in-the...

Much of the benefit of solar and batteries would be obviated by the need to propel their own bulk along though.

Isn’t the idea to eliminate the need for oil tankers?

Even if we move away from ICEs, which will take decades, we will still need oil for things like plastics for the foreseeable future.

Multi layer perovskites could make them worth carrying on ships that have to stop (canals and similar).

If your batteries have to do 2400 out of 2500km and then 2100km out of 2500km in two stretches that's a 10% reduction in battery cost (and a cargo increase).

Even at 6% (high but achievable efficiency in the mid term) it's still worth slapping them on if it doesn't interfere with operation too much as they weigh comparatively nothing.

This is the wrong calculation.

If a ship is already diesel-electric (which many are) then you need to calculate if adding a solar panel saves more fuel costs over its lifetime than its upfront cost.

If it does, then you can add more and keep doing that calculation until the point where the cost exactly matches the savings.

Seems like cargo ships would be less suited to this initally than tanker ships though, since they don't carry items on their flat upper areas.

If putting 265,000 sq ft of solar panels is cheaper than the equivalent battery needed, why wouldn't they do that?

265k sq ft of solar panels roughly reduces the amount of battery needed by 3% to go any given distance, his math says. It is unlikely this costs less than the 3% of battery reduced.

And of course, you can't readily make the whole upper surface of a container ship into panels, because cranes lift containers off the ship.

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