From this period increased knowledge and understanding of hydrodynamics and aerodynamics, coupled to the availability of plywood and reliable waterproof glues saw dramatic changes. Clinker and carvel construction was dropped and glued up hollow pear shaped masts became standard. By the late 1960s a greater understanding of the science behind planning saw hulls made with increasingly less rocker, very fine forward with very flat aft sections. Once trapezes were introduced the number of crew dropped to 4 by the early 70s and then to 3. Designs became wider, especially aft. As speeds increased so did capsizes, so an effort was made to install built in buoyancy and some self draining capabilities with transom flaps, venturi floor drains built in tanks, especially forward and false floors.