One can take drawings for the original ship to a blueprint service and have them blown up, or reduced to bring them to the new scale.
You can easily work directly from the original drawings however, by changing scale each time you make a measurement.
To convert feet (of the actual ship) to the number of inches long that the model will be, use the factors in the table on the right.
To find the principal dimensions (length, height, and width) of a (square-rigged) model in 1/8" scale, then: Although this technique allows you to judge the approximate length of a proposed model from its true footage, only square-riggers will fit the approximate height and beam by the above factors.
To approximate these dimensions on other craft, scale the drawings from which you found the length and arrive at her mast heights and beam.