Properly installed, a 7 point is specifically designed to prevent submarining. Remember that the lap belt must be tight below the hip joint. This combines with the left and right leg straps to capture the pelvis in the same manner that a parachute harness does. To be honest, the center submarine strap is redundant if the leg and lap straps are properly installed and adjusted.
When we worked with Stroud Safety on the ALSR, he informed us that our driver position left us vulnerable in a tumble. For a highly reclined position, the real danger that still exists is the "reverse submarine" where a rear impact (in a tumble, or if we spin and hit a wall backwards in closed-course racing) causes the drive to go up and back on the seat's inclined angle. If the shoulder straps are positioned correctly to restrain the driver from going forward, they stretch too much in a rearward impact or break the collarbones.
The solution in F1 (and soon in all racing) is a 9-point. There is a second set of shoulder straps under the normal ones. They are routed over the shoulders, down the seat back and cross the back behind the driver. Attachments are just above elbow level on both sides. The cross restrains the driver in a rear-side impact. It's completely transparent to the driver since both sets of shoulder straps are mounted to the same buckles. It has the added benefit in fast accelerating vehicles (like formula cars) of keeping the driver down in the seat so his feet don't come up off the pedals.
Stroud supplied us with one, and there was agrrement from everyone who tried on the cockpit that it made a difference in upward restraint. Yes, a 7 point can be mounted so that it restricts upward motion, but only at the expense of forward restraint for a highly reclined position. Remember to add arm restraints and a HANS so that your wrists and neck don't break and you are still able to get yourself out after everything comes to a stop.
