Thunderbirds are wood. Thunderbirds are built in both wood and fibreglass.
Plywood is a pain.
M ore second hand Thunderbirds would probably be purchased if there were more used fibreglass Thunderbirds on the market. The Thunderbird embodies family sailing. Its origins are in a competition sponsored by the Douglas Fir Plywood Manufacturer's Association in the late fifties, to design a quick, stable boat that could be built in plywood and would accommodate four. West coast marine architect Ben Seaborn came up with a design that met all the criteria. It sleeps four, especially if two are kids and all have modest expectations, can be built easily in plywood and delivers superb performance.