Dutch warships in the First Anglo-Dutch Wars with 8-18pdr guns

The Dutch flagship Brederode was the most heavily armed of the Dutch ships in the First Anglo-Dutch War. There was a group of ships that were pretty heavily armed, as well. They carried 8-18pdr guns, along with more of smaller shot weights. Pieter Florissen's flagship, the Monnikendam, although just a 120ft ship, had 8-18pdr guns, along with other that brought the armament up to as many as 36 guns. Michiel De Ruyter's flagship for much of the last half of the war, the Lam, also had 8-18pdr guns. For a brief period in April 1653, De Ruyter used the Middelburg Directors' ship Gekroonde Liefde (36 guns) as his flagship. That ship too carried 8-18pdr guns, along with others. One odd ship, only 117ft x 27ft x 11ft, that had a large complement of 18pdr guns, according to the Staet van Oorlog te Water for the year 1654 was the Rotterdam, commanded by Jan Aertsz Verhaeff. I have seen another document that shows that they might have actually been 16pdrs. Still, if the Rotterdam was only 116ft long and had 18-18pdr guns, they must have been very light pieces and would have had to have been fired with light charges. There was very little space for gun recoil on a 27ft beam. This all seems very odd, and is a mystery to me.