Here's a thread with more info on SeaCraft history, in case you haven't seen it.
potter years?
I believe there was some pressure to cut costs in the mid 70's when the price of resin jumped during the first gas crisis when the Arabs shut off the oil. I know that all 72 and earlier 20's had 4 fg stringers, as described in detail in the Seafari 20 article in the Literature section. This created a VERY stiff solid hull. About 73 or 74, Potter replaced the 2 stringers on each side with one larger box type stringer on each side. It was evidently still pretty beefy, as I've never heard of any problems with them, but the 4 stringer system would theoretically be a little stiffer and would distribute loads better with twice the number of vertical ribs to tie the cockpit sole to the hull bottom.
If you want to learn about the most interesting part of SeaCraft's history, check out Carla's
Moesly SeaCraft web site Moesly was the real genius who invented, patented and raced the VDH design. IMHO, Moesly's old SeaCraft 21 designed in about 1960 is still the best riding model, as it's the one that set all the records in offshore powerboat racing. Potter simply expanded on what Moesly started, building fancier and more expensive boats, but he never raced any of his own designs.