I realized this morning that I have been estimating dimensions, all week, for Rotterdam ships without taking into account my theory about the size. I theorize that all Rotterdam sizes in lasts are based on calculations using Maas feet of 12 inches of 308mm. This is certainly true for ships from pages dating from 1642. My theory is that this applies to all Rotterdam ships from 1600 to 1652, not just 1642.
After a certain date, all Dutch ships were measured in Amsterdam feet of 11 inches and 283mm. The usual last calculations are based on measurements in Amsterdam feet. I always convert dimensions to Amsterdam feet, so we have a common basis for comparison.
