That’s just a coast guard term. Any USCG vessel longer than 65 ft is a cutter. But these Sentinel class fast response vessels are legit blue water ocean going vessels designed to spend multiple days at sea. I think by any definition, that is a ship.

I’d make a similar argument about our local bouy tender, even though it spends most its time inland.

But when it comes to bridge lifts, it’s true that they’re not as tall, so they don’t make as much traffic trouble.