Hi. I recently acquired (for free) a blue, 16' 1" OT Penobscot with HIN #XTC96417H788. It's been under a bridge next to a stream for many years and the thwarts, yoke and and cane seats were rotten (all the wood was recently removed), but the vinyl gunwales and plastic decks are fine. The hull looks good; it was hardly ever used (I know the owner). I know some of the Penobscot's were Royalex and others were a poly material; I'm wondering what this one is. The outside looks like it will clean up easily, but the inside sat with water in it for years, and it's pretty dirty. If anyone knows the safest cleaning product for the material that will get rid of the stains, I'd love to know. Thanks for your help!