Sentence:  As when two warlike Brigandines at sea, / With murdrous weapons arm'd to cruell fight, / Doe meete together on the watry lea, / They <WSD>stemme</WSD> ech other with so fell despight, / That with the shocke of their owne heedlesse might, / Their wooden ribs are shaken nigh a sonder ... 
Meaning of the word marked with <WSD> tags:  To hit with the stem of a ship; to ram.