Question on floor replacement!!

[snoman23]

Hello all, first post here. Somewhat new to boat repair but enjoy it. Lots of good info of all types on this site. Here's my question.
Older 18' bayliner, not quite sure of year. Model was quartermaster. I'm replacing the ply floor and encountered a layer of material resting on the hull, below a layer of fibeglass cloth after removing the foam between stringers. The material seems to be some sort of wood type padding for the hull. looks like it was laid in strips lenghtwise and covered with the cloth which also enclosed the stringers. It was soaked pretty good with water. Any ideas what this stuff is? Do I need to replace it before laying the floor? Also, does the technique of using "sister" stringers work well? I'd like to not have to cut entirely new stringers and heard of this here. Also should the plywood touch the sides of the hull and are the stringers supposed to touch the bottom of the boat? Heard of a 1/2" pad or foam of some type should be below the stringer. Not sure about a few things. Plese excuse all the questions but want to do it right.Thanks for any and all help.
Keith

[jachristner]

I'm looking at a complete floor and stringer replacement and have these same questions. Any help would be greatly appreciated.