SEA SCOOTERS ARE JUST PLAIN FUN. Diving and zipping through the water like a dolphin is the stuff of pure swimming, scuba-diving and snorkeling joy. On the flip side, though, some of the most popular scooters aboard superyachts can be almost 4 feet long and weigh around 70 pounds. Stowing them becomes a space-crunching chore, especially if there are already personal watercraft, tenders, kayaks, fishing gear, inflatable toys and paddleboards vying for room in the lazarette. ¶ For boaters who want their underwater fun to come in a smaller, more manageable package, China-based Geneinno makes the S2 sea scooter ($399). It’s a follow-up model to the Trident—now called the S1—model that Geneinno introduced in 2018. The S2 model is designed to be lighter, smaller and completely portable, weighing 5.9 pounds…