Confession- well it's supposed to be good for the soul
My models are usually started without a drawing of the full size model first. With most, a reduced scale, something like a quarter to a fifth size, general layout sketch has been used. This is good enough to ensure that the design will work, all the important bits fit inside the hull and, just as important, be accessible/removable..!
Yes, problems might and sometimes do occur and result in changes having to be made. But, I've yet to produce a model that will not float and go although sometimes "adjustments" have been called for before satisfaction has been achieved. In this case I'm glad not to have spent a lot of time and effort on first drawing up a detailed and what I foolishly believed was a "perfect design". Any plans drawn up for publication have been based upon the final successful and thoroughly tested model.
There have been a few occasions when I had to draw a model out fill size before building though. Once was a large liner and I couldn't get the right appearance with the reduced scale drafts. It was a bit like "Goldilocks" two funnels weren't enough, four too many but three, just right..!
Glynn Guest