As noted in my previous post, I am currently planning a series of four boats. Their plan lengths are 7'-10", 14'-0", 25'-0", and 43'-10". I started playing with the proportions between one boat and the next. Rounding these proportions to 2 digits, I got 1.79, 1.79, and 1.75. Almost a geometric progression!
I like this kind of thing. To make it perfect, I revised the length of the final build to make its proportionate increase 1.79 also. This would make the last build 44'-8", an increase of 10". According to the folks on the Glen-L forum, it is easily feasible to extend of length of any Glen-L design by up to 10% by increasing the proportionate spacing between the frames by the same ratio. A 10" increase amounts to a little over 1.5%. Good enough.
Would I build a 5th boat, either larger or smaller in this series? Not likely. On the short end, the next smaller size would be about 4' 7". This might make a nice R/C model, but not a practical boat. On the big end, you're looking at about 80'. Not impossibly large, but a little rich for my blood, and WAY more than needed for non-commercial use.