police marine units/police swift water rescue

I understand where you are coming from, but New York is a special exception to the rule. The rest of the world, at least Western world, for the most part, has Swift Water Rescue handled by Fire Rescue services more often than Police Rescue. This is simply a logistics thing, as most police departments are not the size of the NYPD and do not have the budget and resources required to train and have ready a SWR team, whereas fire departments are more likely to meet this requirement as it falls under the mandate of their services.

I don't play in NYC, but I would imagine those who do place ESU stations as Fire, rather than Police, given their primary function seems to be more of a fire service than a police service.

Helicopter water rescues in my experience working as a rescue tech are a last resort, and generally something we only do when there is no reasonable means to rescue by watercraft. Helicopters create a lot of downwash and make it extremely crappy for those in the water, who now have to deal with what amounts to a lot of small waves coming directly at them from their rescuers. Usually water rescue is carried out from boats because it's a much more pleasant rescue experience for the victims, and is significantly cheaper on agency resources than using a helicopter.

Haven't had a whole lot of playing with the new boats yet, but my understanding is they're supposed to be a RHIB type vessel, meant for more of lake and shore rescues than sea rescue as well, which is a little different than what you would use a helicopter for, which is more sea based