Just launched at the Monaco Yacht Show, the Seakart 335, a combination of a RIB, a jetski and a yacht tender, is billed as “the ultimate sea toy.” It may be, but whatever it is, it looks like a lot of fun. Powered by a 110-hp or a 180-hp gas four-stroke Yamaha jet engine, the Seakart can hit a top speed of 45 mph, and hold up to five people – two in the bow and three across the stern. It has fiberglass parts and inflatable Hypalon tubes, so it is appropriate as a yacht tender as well as an…