Very muddled thinking here. My Bav 37 displaces 5.36 tonnes. Its "capacity" is 8 crew, which at 80kg a person is well over the 1/2 tonne you suggest! I don't have the full RCD certificate with me but like Fullcircle I recall a figure of around 2 tonnes.

Anyway, it is not weight per se that is important, but where it is placed and how it used. Big lumps of lead at the bottom of a boat serve little purpose except to require heavy construction to take the loads and reduce the volume of overall space that can be allocated to other uses.

As to load carrying capacity, this is a function of waterline plane area, not weight. Lighter displacement boats sink less than heavy displacement boats for a given weight. Suggest you go back over PBO back numbers for a series of articles on the subject by Andrew Simpson (who lives and cruises aboard a very modern boat of his own design).

The Fasnet event is not a good example to use - mainly because the boats that were most criticised were built to IOR rules and much of modern design thinking, particulalrly on stability has developed in response to those criticisms.