Div 2 were rounded bottoms; more akin to a small yacht. Div 1 were flat bottoms. There were a couple of boards that sat between the two. Think one was called the Laser Surfsprint. It had a rounded hull in the nose and flattened towards rear.You couldnt race it in either. Well you could in Div 2 but you had no chance but it was banned from Div1)
Most recreational sailors had Div1 but that slowly changed to funboards. Shorter; flat boards but not really competitive in Div1. Div 1 max length was 375cm.Think there was a max volume too.Sucessful Div 1 were F2 lighning.Sailboard sport.etc.
Div 2 had enourmous displacements.as high as 380 litres I (could be wrong with figure but they were massive) They rolled worse than a canoe when you stood on them; you only had any stability with the great big centre board/dagger down. Most were hollow.Amazing technology.Normally coremat construction. (ie two layers of fibreglass seperated by a core of cork. (or similar) after a days sailing you had to empty them just like a dinghy. (They had drain bungs !!!) Lenght was upwards of 380 cm; width around 65 cm.
Those were the days !!!