The smallest ships from the Dutch First Anglo-Dutch War building program

I don't understand the rationale for this, but both the Noorderkwartier and Amsterdam built smaller ships for part of their contribution to the two-30-ship building programs. Examples built by the Noorderkwartier were 130ft x 32ft x 12ft. Two of these were the Caleb (built in 1654 at Hoorn) and the Jupiter (built in 1653). An example of a small Amsterdam ship was the Dom van Utrecht (built at Amsterdam in 1654). Her dimensions were 130ft x 32ft x 13ft. The Zeeland ships built to the 130ft charter tended to be larger: 130ft x 34ft x 13-1/2ft. The Zeeland Dordrecht and Kampveere were built to these dimensions.