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Comment by zeristor | Hacker News Reader

Cars have regenerative breaking which is a help in urban areas.

Ships tend to go not change course nearly as much on a several day journey. I guess a propellor could run in reverse for regenerative breaking, but it wouldn’t help much.

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Ships are subject to so much drag that this is rarely a problem, only in emergency situations and there is not much that you can do to stop a vessel that weighs 100,000 tons or more except to run your engines in reverse and start praying to your deity. Regenerative braking for boats would be a complete waste.

There are some vessels that have single use emergency brakes, but the latest trend is to have motor 'pods' that are electrical and that can be used both for normal propulsion as well as to perform emergency stops that are quite impressive given the size of the vessels they are on. Typically an oceangoing vessel requires at least 3, but commonly 5 to 10 ship lengths to come to a full stop from moving forward under power. This is not necessarily because of limitations of the propulsion unit, but simply because stopping that much tonnage too fast would do as much damage as a collision would. With classical engines there is far more rotating mass so it would take much longer than with electrical propulsion to react before the beginning of the braking phase.

Regenerative braking for boats would be a complete waste.

Unless you have a large sail to generate thrust to spin the propeller...

It’s a pity that the sail isn’t also PV solar.

Pods are used primarily for manoverability. This allows Cruise ships to get in and out of ports with a minimum of assistance (none at all, if conditions permit). This is important because they are entering and leaving ports every day or two. It also makes sense as the hotel loads on these floating skyscrapers is similar to the propulsion loads so having combined main engines and generators gives other advantages.

Ocean going container vessels on the other hand use massive direct drive two stroke diesel engines (usually they only have a single engine). They have no gearbox. The only way to go-astern is to literally start the engine in reverse. This can only be done up to a limited speed, otherwise the windmilling effect of the water passing through the prop would overpower the starting air.

Suffice to say, I'd put a long bet on the overwhelming majority of containerships being powered by internal combustion engines in 30 years time. If we get our act together we might have come up with an alternative / synthetic fuel by then but I wouldn't hold my breath.

> Pods are used primarily for manoverability.

Check out the https://swzmaritime.nl/news/2022/11/08/how-abbs-braking-syst... 'wonder of the seas' e-brake system.

It's interesting but it's just an automated system build on top of the existing pod drive architecture which is there for the reasons I suggested.

Interestingly, there are situations in which it might be helpful where it wouldn't have worked. For example, the Francis Scott Key Bridge incident. The vessel suffering from a blackout caused by a transformer being tripped by a single loose wire.

Yes, new technology enables other new technology. The e-brake potential of drive pods was recognized before they were put to practice, and the jury is still out on whether or not it is the way of the future. But it is something that simply wasn't possible before at all unless you wanted to risk a snapped drive shaft, you can't just throw that much rotating mass into reverse without consequences and the driveshafts of a liner are most impressive, I've stood on a lathe that could cut them, and that thing required it's own building and power hookup just to spin the shaft up in a reasonable amount of time for machining.

> The vessel suffering from a blackout caused by a transformer being tripped by a single loose wire.

Transformers don't 'trip'. Circuit breakers do.

Yes, it was a loose wire. But that vessel had regular diesel propulsion so that is not going to make any difference, loose wires can - and do - happen, usually with less far reaching consequences.

The point of the pods is that there are many of them, and they are somewhat redundant reducing the chance of such complete outages. It may well have prevented that particular accident but it may have caused another. This tech is just too new to draw any conclusions.

As far as I understand it every pod has its own dedicated power infrastructure section (batteries, drivers), with the ability to maintain symmetrical drive even in light of multiple failures. So these are right now not for normal propulsion on ocean going vessels (though in a diesel-electric setting they could already be used like that and there are a couple of vessels that use them but I'm not sure if that is for main propulsion as well), but these 'captive torpedos' definitely have a lot of potential.

> Transformers don't 'trip'. Circuit breakers do.

I'm not sure what this pedantry adds. It's pretty common to say that a piece of equipment tripped for example whole power stations, a generator, a pump etc. When of course it's the circuit breaker protecting that equipment or even occasionally something like a physical over speed trip.

The pod drive architecture, and diesel electric more generally, only makes sense when the other benefits outweigh the efficiency losses of converting from mechanical to electrical and back again. It's very difficult to beat a shaft connected directly from the flywheel to the propeller.

Isn’t regenerative braking reclaiming otherwise wasted energy from necessary deceleration? Running the propeller in reverse would result in having to apply equal or greater energy to regain the current speed, so it’s a net loss of energy if I’m understanding the suggestion properly.

Not changing course is good though. Regenerative braking is only good because it increases the efficiency when you absolutely must slow down, but it would always be more efficient to slow down less.

Wind, large surface area for solar

Also wave based generators that could also act as dampers/suspension and they wouldn’t steal energy from forward motion like wind would (depending on if you’re generating wind energy or using wind to buttress the batteries).

Ideally a combination of sails coupled with batteries and wave generators sounds like it would be very energy efficient.

Solar on board of cargo vessels is a pipe dream, as is 'wave based generation'.

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