Hi Gareth,
Let me explain briefly about hull/boat design. Boats are designed with numbers, many many many numbers and ratios of many numbers and numbers raised to powers, etc. Long before the first hull line is put on paper, that hull shape is described in terms of numbers which are necessary to meet various requirements for the hull design. The same is true for the mast and sail plan and the centerboard and rudder. It is all numbers. The last step is to draw the picture, the geometry, that satisfies the numbers, the ratios, etc.
To draw use CAD and draw pretty pictures of hull shapes without knowing and understanding the numbers, the rules and the goals, of the hull design leaves many many unknowns which could be called guesses. The beauty of running the numbers first is that if some performance or behavioral characteristic of the design is undesireable, change the numbers, iterate, until a satisfactory solution is found. It is much quicker and less expensive to do it this way.
Bill