Computers and CAD are wonderful for taking a design and rescaling it to create bigger or smaller clones. In theory they can do all of the work for us and then we print the drawings of the new design. Designing stuff is easy, isn't it?
That is fine if all is scaled up by the same proportions. Open a drawing, tell the program to rescale by the amount you want, adjust here and there for differences in material thicknesses, refit the result to the output paper size then hit print. But!!!!!! Make the proportional adjustment in one of the 3 directions different from the others and the situation changes completely. Shapes of all sorts of things change in ways that can be awkward. Circles become ellipses, squares go out of square and angles change. To simplify the whole issue I keep the proportional change in width and height the same so that the overall section shape doesn't go out of whack and the structural sections used for stringers etc don't go out of square.
Working with the Didi 26 as the starting point, I blew it up in all directions, more so in width and depth than in length. Next came another 100mm of freeboard, done by extending the hull sides upward without changing the side angle, so the deck became wider and the overall hull shape remained unchanged. After that I added another 100mm of height to the cabintop and adjusted stringer spacing to give a sound structure.
This all ended up as a large amount of redrawing for the structure. After all that the rescaled interior had some oddities, so I reworked that as well to make it work better. Final changes were reducing the cockpit width from the racing type of the 26, adding coamings for comfort and to give cubbyholes for winch handles, ham sandwiches etc, and a saildrive inboard diesel in place of the transom-mounted outboard.
The final result is a boat that will be a nice coastal fast cruiser. It will be light and stable enough for excellent speed, yet still able to get into shallow water. It will also follow the lead of the Didi 26 by being a great club racer. The sail plan is slightly more conservative than that of the Didi 26, yet this boat will still be fast enough for some exciting sailing.
More info on the Didi 28 is at http://dixdesign.com/28didi.htm .