Morning, doing a quick google I get there to be two different lenghts for the full size boats one at 88 ft and the other at 96ft so:
88ft = 1056 inches 1056/50= 21.12 so thats 1:21
96ft = 1152 inches 1152/50=23.04 so thats 1:23
both are within a knats whisker of 1:24 scale
remember a 6ft man at 1:24 scale is 3 inch (75mm)
but a 5ft 5 inch man at 1:24 scale is 2 5/8 inch (67mm)
so you can get away with small differences in scale ( Airfix do it with 1:72 and 1:76 vehicles)
unless the rivet counters are about !
Gary 