The coordinates in the VERT block are relative to the center of the boat in neutral position. In Commandos an object is in neutral position when it's facing right, the center of an object is defined in the ANM file.
For example: In LANCHON2.ANM, the line SPRITE "LANB0006.RLE",-43,-116,0 means that the center of sprite LANDB0006 is at 43,116 on the actual image.
.VERT [ [ 250 0 ] [ 210 70 ] [ -60 45 ] [ -60 -45 ] [ 210 -70 ] ]
.VERT [ [ 220 40 ] [ -60 40 ] [ -60 -40 ] [ 220 -40 ] ]
And like the sectors of the navigation mesh, also the RENDERVOL and VOLCOLISION polygons have to be convex!