Slideblues - you sure have an eye for design features... fun stuff, isn't it!
1. That inside runner is called a 'lift strake' or 'spray rail'. Lot's of controversy in design circles re: it's value. The placement height of the spray rail is very important to it's functionality, and proper location can really help to 'pop' after setting hull in corner, and can prevent over-wetting at lower speeds.
2. The vertical fin or 'fence' is intended to act to prevent air spillage or 'wing-tip' vortices that contribute to aerodynamic drag. I am not always convinced that the fences save more drag than they create, as they can often heavily disturb the laminar flow of air over the main 'wing' section of the tunnel.
3. The drop in the tunnel roof (floor) was initiated in the 1980's to lower the height of the driver, resulting in a lower center of gravity and a reduced bluff area presented for aerodynamic drag. Advancements in mod-vp style hull designs proved the potential contribution of hydrodynamic lift from this center 'sponson', and it became more prominant. They can now be designed to aid substantially in acceleration through lower velocities and recovery out of turns.
4. The full length strake (outside) has the same benefits as the 'spray rail' on the inside tunnel. Location height is really important.
5. The 'flat' center section is a much more efficient aerodynamic lifting surface design. (Look at aeroplane wings...they are all 'flat' throughout the wingspan, right?) The 'flat' design isn't used by many designers as much as it could though, 'cause it often doesn't look as 'cool'.
6. Lower frontal area - less is always more! Less frontal 'bluff' area generates much less aerodynamic drag, particularly at higher velocities. A one (1) sq. ft. area produces 4 times as much drag at 60mph as it does at 30 mph. Less is better, and streamlined airflow design is even better.
Fun stuff, isn't it. I love it!
/Jimboat
Secrets of Tunnel Boat Design