To find out how the Marine Patrol will determine who is speeding, my advice is that once the law is in effect, that you speed across the Broads as fast as you can in your gas-guzzling power boat and wait until you get caught. At that point, you will no doubt learn how they intend to catch boaters breaking the speed limit. Perhaps when you contest your fine in court, there will be other details that you will learn about.
Similarly, when the Laconia Police department, stops and fines me for speeding on Route 11, I learn a great deal about the methods they use to determine that I was speeding. It is a wonderful, if not expensive, learning experience.
I can't believe you guys are asking these questions! How about not speeding?