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Comment by krschultz | Hacker News Reader

As someone that has designed (military) ships, here are my thoughts.

- LNG is definitely happening, and that alone will make a massive difference in emissions.

- No shit smoother bottoms and bulbous bows are better for efficiency, that's been standard practice for decades and large cargo ships are generally not that old.

- Counter rotating props are interesting, I could see that being a big win but the mechanical complexity might not be worth it. Cargo ships are generally kept pretty simple for reliability.

- I doubt we'll see widespread wind or solar power any time soon. The dynamics of wind turbines on top of a pitching platform get pretty wild quick. The energy density of solar doesn't seem high enough.

- Lol, get the fuck out of here with the idea of nuclear power for cargo ships. The US Navy doesn't even bother with that complexity for anything other than subs & carriers where it's the only viable option.

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> As someone that has designed (military) ships

Hey, me too! I see you were at Electric Boat. I was at NAVSEA HQ at around the same, probably making your life difficult. :) Though I did surface combatants, not subs.

Someone had to keep us honest! Fun work, I would have stayed longer but I moved to another area for family reasons.

I think the biggest win for wins in the near term will be kites, not full-on sail rigged ships.

See my post in this thread. Kites have not taken off. I don't know why.

This will be dependent on big advancements in shore based electrical power costs in the future, but is not totally far fetched:

1) ridiculously low $ per kWh electricity from multi hundred megawatt scale photovoltaic plants may may cracking hydrogen from seawater economical. It takes a ton of power, but if your power is almost free, it can work.

2) store the hydrogen. This has its own technical problems but in terms of energy density can replace heavy fuel oil

3) power ships from massively parallel arrays of hydrogen fuel cells, driving electric thrusters such as current generation large azipods.

Or, if there is some amazing advancement in Wh stored per kilogram/cubic meter of battery, in battery technology generally, skip the hydrogen step and have short to medium range small cargo ships the size of "geared" containerships which recharge in a fashion similarly to the upcoming Tesla semi tractor.

> LNG is definitely happening, and that alone will make a massive difference in emissions

An important, if often repeated point: Natural gas reduces emissions at the point of consumption; that may be balanced out by higher climate change impact when it's mined.

If someone has good, conclusive information on that issue, it would be appreciated.

Based on what? Lots of Natural gas was just released into the air at oil fields before they started capturing it for sale.

People mean different things whey they talk about emissions. Shipping is particularly dirty because of the low-grade fuel that they've been using. Its very high in sulphur content, and typically contains a higher fraction of heavier compounds that don't burn as well.

So the ships produce more unburned hydrocarbons (smog precursors) and sulphur oxides (acid rain precursors).

So even if the total CO2 emissions are similar, the other toxics are still greatly reduced.

So... can we produce LNG without producing Diesel? I thought crude oil mandated the proportion, and it was a “good thing” that we found some opportunities to consume the Diesel part? We can’t convert the whole world to LNG because we’ll have way too much Diesel left.

We can produce natural gas, thence LNG, from natural gas reservoirs, which contain very little liquids. Eg. coal seam gas can be 95%+ methane, and essentially zero diesel.

>that may be balanced out by higher climate change impact when it's mined.

What do you mean by that? Natural gas is taken from oil wells, the exact same kind of holes in the ground that produce bunker fuel. It's the highest level on the refinery column.

Edit: Here is a picture of the gas market right now:https://en.wikipedia.org/wiki/Gas_flare#/media/File:Niger_De...

If LNG pans out we would move those fires into the engines of ships. It would probably be carbon-neutral up to the trucks that the pipe welders drove.

> Natural gas is taken from oil wells

There's a large boom, not new at this point, in extracting natural gas via fracking. My understanding is that the process produces emissions with high impact on climate change.

Increased production (and the associated environmental risks) would happen no matter what we were burning. Switching between two fuels doesn't change the amount that has to be produced: if for some reason we couldn't burn natural gas, the same increase in energy consumption would cause the same boom in fracking other oilfields in order to satisfy the demand for the other hydrocarbon.

Edit: If the concern is that the economics of NG are driving higher consumption, then you've got to realize that you could still reclaim the net win by doing some legal thing to halt consumption. The important variables here are damage per consumption and consumption: you want to lower both, but if an improvement in damage per consumption raises consumption you don't want to go back and make the damage per consumption worse. The only reasonable course of action if the damage was too high would be to go in and say, keep using the least-damaging fuel but you're going to have to burn less of it.

I have some information...

1. When methane is burned, the carbon dioxide emissions are about 30% lower per unit energy than when liquid fuels are burned (50 g/MJ for methane, vs abt 74 g/MJ for liquid fuels) 2. When LNG is produced, an additional ~10% CO2 is generated, via energy consumption in the gas liquefaction plant 3. Methane leakage from production plant and pipelines is estimated at about 3% of total. This adds a greenhouse gas effect of about 63% (since methane is ~21 times more potent than CO2, greenhouse-effect-wise). 4. Pollutants such as sulfur oxides and soot from natural gas combustion are essentially nil. Heavy fuel oil for ships can have a very high sulfur content.

Sooo... it is quite possible that natural gas use has a higher climate change impact, due to leakages. For other pollutants, natural gas produces less.

Thank you! There is no substitute for actual knowledge.

I would expect counter rotating props to be more reliable. Instead of one big engine/prop you have two smaller ones. While it is more likely that something will break, it isn't a catastrophic failure: you continue to your destination using just the other engine/prop.

More reliable than one propeller, sure, but many (most?) large ships already have multiple, don't they?

Counter rotating props run off the same engine(usually how its done) would offer nothing in terms of redundancy if anything fails.

Just because you replaced 1 thing with 2 things doesn't mean you've increased the system's reliability. In this case, you've also added a lot of complexity in the shafts, seals, and gearboxes. That means more things that can go wrong. Most of those things can affect both screws when they fail, so there isn't any gain in reliability due to redundancy at all.

Note that they're not talking about two separate props on separate shafts, they're talking about 2 props rotating in opposite directions on the same shaft. Many ships don't have a 1:1 ratio between propellors and engines anyway, if 2 separate shafts & props were faster they could do that easily. But counterrotating on the same shaft adds more critical moving parts in an already sensitive area.

I stand corrected.

What about solar? I know it does not scale down very well or work for the military, but solar seems useful for the largest ships.

MV Barzan is a container ships that's 400 m x 58.6 m. If you take say 400m x 50m * 24% solar panels that's ~6500 HP in full sun. I know the engines are significantly larger than that but not sure how much they use at cruising speed.

Quite a few large container ships have 100,000+ HP combined. How much they use at cruising speed, I'm not sure.

That is not nearly enough. These ships are heavy. To put it into perspective, 6,500 HP would be just enough to meet half the auxiliary power demand (eg, HVAC, electrical, motors, etc) on the 500-foot training ship I sailed on, which is a toy compared to commercial ships. Propulsion required a 60,000+ HP steam power plant.

How unfeasible would folding solar panel arrays be? The ship could fold them out like a satellite once they left port if the seas were favorable.

Solar can produce a great many kWh per month if you cover the roof of a whole Costco sized warehouse with it, but for instantaneous power is nowhere near sufficient for large ship propulsion. The energy density in joules per kg or liter of fuel in compressed gas or heavy fuel oil or diesel is significantly higher than what is now possible with batteries. Where pv might have a role is shore bases charging stations to charge short distance electric cargo ships, such as the privately run ferries that transport tractor-trailers from the Vancouver metro area to Vancouver island.

Providing 100% power is clearly not going to work. However, it's vastly lower cost energy than hydrocarbon fuels. Cutting down fuel costs by say 2-5% is still worth a lot of money over 20 years of operations.

I am more curious about the scale of savings and the costs of trying to have a solar on top of the ship.

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