Racers shut away for a week incommunicado and airport-style metal detectors — powerboating in Japan deploys strict measures as one of only four sports in the country that can be legally bet on.

Powerboat racing started more than 70 years ago under a special gambling law that classifies it alongside horse racing, speedway and cycling in Japan.

The niche sport, which has seen 30 fatal accidents, has long been in the shadows because of its close association with betting.