the boats are generally weighed by suspending them from roof beam with spring balance. from memory the rudder system comes off completely as well as anything that is attached by a shackle also all ropes. you can however do it with bathroom scales under one side at a time. the most accurate, as you point out is to have the platform as level as possible. a ten degree angle may make 500 - 1000grams difference. but if its that heavy 35 kg per side i doubt whether you could do much more than pray for wind like i do. i am also 95 kg and unlikely to weigh 75 in the near forseeable future, unless they make iced coffee illegal, and pies and chocolate donuts..........mmmmmm donuts