The wood is most likely OK. Before you try sanding out the stain try some oxalic acid on the wood. You can get this at any good paint store (forget the big box stores) Also, you can try a type of product generically called "Deck Brightener." This product usually has oxalic acid as an active ingredient. Try this on a scrap that has water stains before trying it on the boat parts. Or try it on the undersurface of the boat part if you don't have any scraps.

Dusty

Hey Chucko, Dusty's on the right track but if you've never used oxaic acid before I'd suggest you try a product called Teak Wonder. It's a two part and it's the best of the "deck brightener" type products. The neutralizing agent (part 2) will allow you the control to do real finite stain removal. As directed, the wood must be wet when applying part 1. Hope this helps. SEEYA Jack

Above is valid advice but you may have to treat the entire surface of each panel in order to achieve a uniform color and hope it stays that way once resin is applied.  I'd try a sanding before using chemicals.  I think you'll be surprised. If sanding doesn't work, then I'd go with the chemicals.  Good luck.  Jer