One of the things I've always felt was a bit odd was that so little time aned thought that is spent on shaping the way the air is allowed to exit through the bottom of the cowling.  For pue fluid dynamic reasons, it should be a lot rounder on the back, not just spilling off of a square corner from the firewall.  For my race boats, I "sculpt" all through hull exits to have a sharp leading edge and rounded trailing edge and also aim them aft to further reduce drag.  This helps the water flow off of the hull more cleanly than just having a hard corner.  It would take some room away in the floor by the rudder pedals but enable more air to pass through with less drag since the rounding of the edge there would create a low pressur area and tend to suck out the air more efficiently.  We use the same principle in some types of bailers for racing dingys and rowing shells.  These have little doors that open and suck out water in the boat or others have cavities molded in with just a plug that sucks out the water at relatively low speed.

 

Dan Newland