alt Hacker NewsShips 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.
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Regenerative braking for boats would be a complete waste.
Unless you have a large sail to generate thrust to spin the propeller...
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.