Early model A/S boats made in Opa Locka Fl. were made with plywood stringers, this was a carry-over from the off-shore race boat method of building during the 70's. The plywood was marine grade plywood, and yes it does rot and can be replaced. The good news is that like the off-shore race boats that preceded A/S the heavy 24 oz. woven roving laminates were so heavy they could support the structure with or without the wood core! Unfortunately the the wood floors also used back then would also rot and the proper thing to do is to replace the floors and stringer cores. If you noticed the addition of certain Fiberglass supplies recently added to the Parts Site it is because I am "walking" Doug Rex up in Michigan through this exact process! The same materials used in my shop are now available for this repair, and instructions are being written for the procedure. There are right ways and wrong ways to do this, and the wrong way is to simply cut the old stringers out and grind down the entire hull and start over. (this only works if you can put the hull back into the original mold to hold the shape, otherwise you will deform the hull)
Fir stringers came around 1983 or 1984? 1985-1991 for sure, 1992 WESMAR started experimenting with nida-core, 1996+ were structural foam cores.
The bulk of the A/S boats have Fir or some type of composite stringers
