The only SeaCraft that had wood stringers that I know of was the very first one, the very rare 21 built by founder Carl Moesly, starting about 1961. He used spruce because it was light; they were covered with fiberglass that carried all the load. By the time he started building the 19 Bowrider, he had come up with a
fiberglass grid system. I'm guessing that was about '64 or '65, but Carla would know for sure. You should check out her
Moesly Seacraft web site for the straight scoop on early SeaCraft history. When he modified the 19 mold to create the 20, all of his 20's had 4 fg stringers; the keelson was a fg encapsulated 2x4 in the 20. The earliest 20 I know of was a '69 vintage but there may have been some built in 68. Potter just continued what Moesly had started when he took over about 1970, so all his boats had fg stringers. Also not sure about the stringers in the Seamaster 27, but No Bones could tell you. I suspect they were fg also.