I guess you can call it imitation hydroturf, it's a diamond plate 4x8' sheet of foam acadeny sells to put under workout equipment. I think this is it, they had them by the exercise bikes, the guys on mudmotortalk.com recommend it as a cheap alternative, but I will say it is not as tough as hydroturf, but should be plenty good for a non commercial used boat that kept covered like mine. I am looking forward to frogging with it under my knees.
http://www.academy.com/shop/pdp/bcg-...ildCatid=34561