There are a ton of different things you can use or get recomend to use. I had really good success with these 2.
I used this alot and some is over and 1.5 inches thick. I like it becuase it already has fiberglass hair mixed in.
http://resurfacesolutions.com/pc-35-...filler-qt.aspx
For the fair below the water line, you can use Quick Fair. Its Pricey but I think others will agree it works out really nice and its epoxy so you dont have to worry about the water.
http://www.systemthree.com/p_st_quikfair.asp