I don't like that tunnel. I have boats built for me with my tunnel design. My tunnels are 14" wide and taper from 0 at the front to 5" in the back and I have the tunnel extended past the transom 12". I cut back the extension to clear the motor after installation. Usually 5-7" left. For length I specify 42" from the transom forward below 115/80. For 115 to 150 48" and 60" beyond that.