Wouter, the 100 kg is the all up weight
I should explain that as this isn't a one design class I offer the same basic design in displacements of 100, 110, 115, 120 and 130kg, all you have to do is ask for the displacement you want. Much over 130 and I think it will be a pig, so Im not going to do anything past that number.
The 4 boats that Billy is building now are all the 100 kg version and if you look at the link to the multihull article and the pics of the kids in it....none are remotely close to 50kg yet and probably won't be for quite some time to come, so that version will suit them.
As for boat weight, I don't think the finished boat will make 50kg, probably closer to 46kg when I last redid the numbers, so the design as it stands look right at a max of 54kg for the crew and probably won't be sailed at that weight for some time yet.
Cheers
RG