Having recently become very weight conscious, I did a bit of digging and turned up some info on what Minisails actually weigh....
The class rules say :
3d) The hull in dry condition with all equipment not permanently attached to the hull removed, shall not weigh less than 43.09kg (95lbs). Correctors of wood may be fitted but must not weigh more than 4.53kgs (10lbs).
A few wooden boats were pretty light in the past, but I only heard of one below weight, in an old newsletter, where the builder many years ago claimed some very light weight well below 45kg, but said he had to beef it up a bit later. The lightest boat currently known is 53kg (117lbs).
One of the problems with the foam used in the 60's was that even the '100% closed cell' foam simply wasn't, so by now this may be adding considerably to the weight.
In the real world - here are some examples from old Forum postings:
Wooden Sprite: 54 Kg.
Wooden Sprite Mk2 weighing about 140lbs (64kg)
Blue Monaco (mk1?) 55kg
Mk1 GRP Monaco 53Kg (117lbs)
MK2 Monaco 66Kg
Mk2 Minisprint - 75kg
Composite Minisprint Mk2 Meson (Tom Moore's boat before re-decking) 55kg and after it was redecked
it was around 50kg.