How to repair a Phil Avalon Bullet surf ski?

[chrisb]

I was recently given a damaged Phil Avalon Bullet surf ski. Not my choice of surf equipment and I will just use it to paddle around on the flat days for exercise provided that I can repair it.

The outer plastic shell at the rear has peeled away from the core leaving a 2cm gap. It is still theoretically rideable and will float but I would like to seal and fully waterproof it.

Is it repairable and if so what methods and types of sealers are the most suitable?