In the real world, airliners based on hydrogen are this year’s hot idea.
It’s believed a 737 / A320 sized hydrogen powered airliner would be readily doable enough to be flying at least in prototype form by 2030. On a weight basis, hydrogen has more energy than conventional jet fuel, but on a volume basis not nearly as much. So the airplane has to grow and/or the passenger/cargo area has to shrink. Converting conventional turbines to burn hydrogen is not hard. Manufacturing hydrogen en masse and dealing with supplying major airports with enough of it is the hardest part. And won’t be low carbon unless the electricity source is.
There is a bunch of thought that getting everything other than water vapor out of the exhaust trails left at altitude will be a good thing too. Chemtrails they’re not, but NOx and various carbon and sulfur compounds really don’t belong up there.
A LOT has to go right to meet these timelines. But the race is on. Or at least the contestants are getting dressed.
I do think an ocean liner has a much easier time at it. They’re less volume-constrained, and don’t need such a high power density. The range is so high that you could get away with installing facilities at only a handful of ports as compared to zillions of airports. And they’re big, so they can get away with relatively less sophistication in the support systems.
That said, I’m certainly looking forward to hydrogen-powered aircraft. Short range will be full electric, but unless there are some big step-function developments in battery tech, long haul craft will have to be chemical for many decades to come.
A battery powered ATR-42 equivalent is plausible with almost-here tech. A battery powered RJ-equivalent is ~3 decades from now. A battery-powered 737-size/range vehicle is made of unobtanium. Hence the pivot to hydrogen at that scale.
Hybrid battery + turbine or fuel cell + turbine or even all 3 is being looked at hard. Right now turbines are oversized for cruise to meet the takeoff power requirements. If a battery + electric motor system could provide something akin to an “afterburner” so naturally smaller engines could put out extra oomph briefly for takeoff and, if necessary, go-around, that’d pay off across the entire mission. This same hybrid power logic is also being looked at for helos.
OTOH, for a 737-sized vehicle you’re looking at multi-megawatt motors. And batteries. And wiring. And power control. With aerospace-compatible weight & size efficiencies. That won’t suffer from corona breakdown, arcing, and all the rest at low temps and 200mb atmospheric pressure. A tall order. But being cut and chewed now, with swallowing in the offing.
The good news about an ocean liner is, as you say, many of the contraints aren’t so severe. OTOH, it’s vastly bigger & heavier.
Cruise ships are not at all about efficient transport - they are basically floating resorts. They can and will be made environmentally friendly, however.
A modern cruise ship runs entirely on electric propulsion, so the debate is on how best to generate that electricity. Hydrogen or LNG would certainly seem to be the best solution at present.
"RCCL is collaborating with Finland-based shipyard Meyer Turku to pioneer fuel cell technology on two new vessels, which are set to join parent company RIL’s fleet in 2022 and 2024. Running primarily on LNG will allow them to eliminate sulphur emissions, and reduce production of NOx and particulates. The new-builds will also be able to operate using distillate fuel in ports without LNG infrastructures.
“The beauty of fuel cells is that they produce electricity with zero carbon footprint – the only emission is water,” chairman and CEO Richard Fain said.
Ship design and its impact on the environment is another area of focus for RCC. The operator’s Quantum-class ships have a specialised hull that captures micro-bubbles, reducing drag and improving fuel efficiency by 10%."
I believe we have the technology now to convert airplanes to bio-diesel, which would alleviate some issues. If I recall correctly, bio-diesel is a less efficient fuel than current Jet A, which can complicate very long distance travel but it’s a manageable problem if we really want to get serious about carbon emissions while still retaining such transportation capabilities.
There are various bio-waste to jet fuel pilot projects. As well as LNG to jet fuel projects and bio-matter to jet fuel.
In each case the problem is the vast quantities needed to make a menaingful dent in the industry’s consumption of traditional fossil-oil based jet fuel. Bio-jet on waste cooking oil sounds good until you recognize the USA’s consumption of jet fuel is 15x the consumption of cooking oil. Oops.
The citations are all slightly outdated even though very recent: the shipping industry changed fuels to reduce pollution. There was discussion early last year (2020) about the impact this was having on fuel prices, but in the event it all got totally hidden by the impact of COVID.
Fuel use increases much faster with speed than it does with volume, so I don’t think that the extra fuel cost of carrying more food would be significant. And they’ve already got significant extra volume because they are being hollowed out to put all the passengers on the outside. The problem I see is that cruise liners go in and out of port, stop and go, and run schedules to put passengers in ports in daytime. I think that’s where the significant fuel use is.
No idea what the economics of cruise ships look like these days - but it may be worth noting that the much sleeker passenger liners that plied the North Atlantic route in the early to mid 20th century often lost money, and were propped up by government subsidies (there was a “national pride” factor).
Re: hydrogen (@Dr.Strangelove , @LSLGuy , @bob_2 – my apologies if I missed anyone), keep in mind that the energy density (specific or volumetric) of the fuel storage system can be much lower than the fuel itself. DOE HFTO has targets of 1.9 kW/kg and 1.4 kWh/L (LHV) for cryo-compressed hydrogen storage.
This is less relevant for a ship, as one of you pointed out. Although it’s very important for aircraft, hence the recent rise in attention toward carbon neutral liquid fuels. But even for ships, as Japan looks to import hydrogen from overseas, they’re looking at shipping it in as ammonia rather than as LH2 or CcH2 (although at least one LH2 ship is in operation last I checked.)
Yeah, well said. e.g. thick-walled tanks for pressurized gas add a lot of weight (and some volume) even as they let you squeeze a bunch more fuel into a smaller space. It’s the total system weight / volume that matters.
Here’s Airbus’s latest H2-powered dreams. Powered by French taxpayers’ Euros at least as much as by H2. Not that US taxpayers haven’t funded a lot of aerospace commercial research in our time.
Agreed; it may end up being that ammonia storage is a net win, but ships really are a best-case scenario here for plain LH2. In particular, the insulation requirements grow only to the 2/3 power of volume due to square-cube scaling, as does anything related to that, such as cryocoolers to capture boiloff. And a big cruise ship has an absolutely enormous fuel volume.
Addendum: when doing the math above, I initially made a mistake and calculated the fuel load of the Oasis of the Seas as 62 cubic meters. That seemed kinda low, but not totally out of bounds of intuition. I did the math again and came to 14,500 cubic meters. That seemed completely bonkers; you could fit a large apartment building in that volume. But I did the math again and it was right. The ship is big but I hadn’t quite internalized exactly how big.
Freight trains can be big, but not in a way that takes good advantage of the square-cube effect. The surface area and volume of a freight train (and of any tankage they can carry) are both basically proportional to the train’s length.
The biggest cryogenic standard tanks you can buy from Linde have a ~10’ diameter. I don’t know what you can fit on a train though. I’m sure you could get a custom job for a ship (NASA does it, so why not?), but I can’t tell you how the cost differs.
This. The articles linked in the OP are outdated, and polemics rather than objective considerations. Cruise ships aren’t my thing and they are undoubtedly wasteful to a degree, but so is much first world activity. It’s very hard to do like for like environmental comparisons in any context. The same set of factoids about cruise ships get recycled all over. Many of the factoids don’t withstand a moment’s thought and are clearly more about a hatchet job than anything.
Bulk carriers are highly efficient because they involve packing a big steel rectangular box full of cargo and then motoring it slowly towards destination. The fuel used per unit of cargo per unit of distance carried is small.
I have no doubt that if you treated people exactly the same way carrying them by sea would also be highly efficient. But they won’t like it…
The answer is the same as always: charge carbon emitters the cost of the damage they cause. Cruise ships can then seek out the best way to reduce their emissions, or just go out of business if it turns out their entire business model is dependent on externalizing their costs. The market works quite well for this sort of thing when all the costs are accounted for.
At least some of the articles had statistics. Carbon output numbers for flying vs. cruising are not polemics.
And the point of my OP wasn’t to condemn cruising but to inquire about the viability of ocean liners (which aren’t quite the same as cruise ships) as an alternative to flying as a means of crossing the oceans rather than a leisure activity.
Yep, I figured that much, but I was curious if something between
*luxury and packing 15,000 people into a ship that usually had 3000 passengers, and
*crossing the Atlantic in hours or weeks
was environmentally viable or if in the end flying was the least worse alternative.
charge carbon emitters the cost of the damage they cause
Which is calculated how? It’s probably possible to kludge together a method but it’s very easy to bias these things to get the outcome you want.
And ironically, one of the reasons that cruise ship figures come out so high is precisely because they don’t have the ability to externalise their costs to the same extent as most businesses. A cruise ship is not efficient, for sure, but the figures are made to look much worse because they are somewhat self sufficient. Much that gets externalised for, say, a land based resort gets counted against a cruise ship because they don’t outsource as much.