Wouter,

If following a weight reduction we only reduce width or only reduce length or only reduce height, the boat will result slower. The right procedure would be to scale down the entire hull in proportion to the weight reduction, so that the original shape is maintained. You proved this point well, but forgot to define some necessary conditions for this to hold true:

Firstly, we need that the initial hull shape is already "ideal" for its weight. If it isn't, reducing only one dimension might actually improve the shape.

Secondly, the crew weight should be reduced in the same proportion as the boat weight, so that the original hull shape remains "ideal". If it isn't, there will exist a new "ideal" shape and a single dimension modification could work well (although different reductions in each dimension would work best to adjust the shape)

Lastly, the sail area should be scaled in the right proportion (not linearly, of course), so that the original hull shape remains "ideal".

Bill Roberts likes to use this type of rationale and posted something along this same line of thought in this forum some time ago.

Cheers,
Luiz