Think about how long your average ride lasts at your local spot. Depending on the type of wave, it’s likely only a few seconds—double digits, tops. But Ben Gravy has made a career out of seeking out the weirdest, most unconventional, and in this instance, perhaps one of the longest waves on planet earth. The novelty-wave specialist recently traveled to Nova Scotia, Canada, in search of one of North America's strangest surf phenomena: the tidal bore on the Salmon River. Powered by the legendary tides of the nearby Bay of Fundy, the river produces a slow-moving wave that surges upstream, offering rides measured not in seconds—but in miles. It's a completely different kind of surfing. Instead of racing down the line on a pitching ocean swell, Gravy found himself gliding endlessly inland as the river reversed direction beneath his board. The wave may only be knee-high in places, but what it lacks in size, it makes up for in endurance. And endurance was exactly what the session required.…