Boat seat base
FIG. 1 is a perspective view of boat seat base showing my new design. The broken lines are for illustrative purposes only and form no part of the claimed design. 
     FIG. 2 is a side view thereof; 
     FIG. 3 is an opposite side view thereof; 
     FIG. 4 is an end view thereof; 
     FIG. 5 is an opposite end view thereof; 
     FIG. 6 is a top view thereof; and, 
     FIG. 7 is a bottom view thereof.