[SideburnsOfDoom]

Q:

> when will they charge?

A:

> The ship... will travel between the ports of Buenos Aires, Argentina, and Colonia del Sacramento, Uruguay. The two cities are 60 kilometers apart, a distance it is expected to travel in 90 minutes.

> Direct-current charging stations will be installed at each port... A full charge is expected to take just 40 minutes.

https://spectrum.ieee.org/electric-boat-battery-ship-ferry

[bryanlarsen]

Full charge is 40 but the charge for each journey is 6 / 9 minutes.

Big difference, since I imagine the turnaround time on a similar ICE ferry would be less than 40 minutes but more than 10.

[SideburnsOfDoom]

Indeed, the turnaround time necessary for unloading passengers, and loading the next lot is likely sufficient to keep charge.

[jillesvangurp]

Something people overlook with these things is that you don't actually need to fully charge batteries because they won't be completely empty and probably a 70-80% charge is more than enough for a single crossing with a healthy safety margin. Also charging speeds are non linear. Charging speeds typically drop when the battery gets closer being full. Charging from 80% to 100% is a lot slower than charging from 20% to 80%. And depending on the battery chemistry, completely discharging or charging them to the max isn't necessarily great for battery longevity.

Another point with battery powered ships is that the rate at which they discharge is speed dependent and that's a non linear relationship because the drag increases quadratic with speed. So, if you are at 30%, you can still make it across. Just not at the full speed. This is less about range anxiety than it is about just being able to stick to schedules. If the ship did not charge enough it would have to go slower. But it would still get there. This ship is designed to go quite fast which means it would have a lot of wiggle room. So they might make it across at full speed even at maybe a 60% charge. The risk is that they'd run low and might have to slow down a bit. It would get there but with a delay if that happens. And then it would have to sit there a bit longer recharging leading to more delays.

The trick is optimizing the amount of batteries to minimize turnover and delays; not around being able to charge them from 0 to 100%. The sweet spot is probably around the 20-80% mark, meaning you'd want to be able do a crossing at full speed using about 50-60% of the battery capacity. The rest is just there as safety margin to avoid delays. If you burn into that, you need to charge a bit more. With 40-50 minutes turnover, there's plenty of time to do that typically.

[SideburnsOfDoom]

Indeed, that's why I say "keep charge", i.e. be in a steady state such as always leaving at 80% charge. Not charging from zero, and not necessarily charging to 100%.

People who charge electric vehicles at home emphasise that you plug it in as a matter of routine every night (ABC: Always Be Charging) and since it's software-controlled, you can e.g. tell it to charge up to 80%, and figure out the most cost-effective way to do that by 8am.

The ABC of such a ship, is that it would be plugged whenever it is docked, during the turnarounds. And there is enough time in that turnaround to keep charge. It likely also has some downtime at night as well, but that matters less in this case.