I know I don't have a dog in this fight but it has always frosted me when a rule goes into the books that tries to solve a percieved problem but misses the point.  OK full length stringers will make a boat stiffer in the longitudinal axis and requiring the seats to be bolted to them enshures that they stay where they need to be.  The rule assumes that the motor is also bolted to the stringers but doesn't state it.

My beef would be if the boat was ENGINEERED not to have stringers at all that the longitudinal stifness was created due to it's shape and materials used and the engine, seats, tanks, whatever were attached to ENGINEERED bulkheads that would stiffen the boat latterally the result would be a stiffer, lighter and SAFER, therefore better boat. 

I'm not saying everyone should go out and try to make a semi-V work without stringers, but a tunnel could work if ENGINEERED.

Now lets look at the rule as stated.  It does not consider the size of the stringer, Is it tapered, notched, straight?  What's it made of, wood, plastic, metal? and what's it's thickness, 1/4",1",1.5"?  Then it talks of reaching to the bulkhead.  Do the rules require a bulkhead? They imply it but again what, where, how, and why are all missing.

If the rule was to assure that the seats stay in place then it should be something like... " seats or seat frames shall be designed and installed in such a way as to provide a minimum of 4G lateral force considering the weight of seat, frame, and occupant(s).

If the rule was to stiffen the boat assembly then some sort of deflection test should be created.  That would also be a great tool for deseigners to follow.

I don't think a 1970 Glen-co chopper gunned, 1/4 stringer boat should go out and race at all it would be suicidal.  But I think as the old (and I mean OLD) rules stated that if the Race Director or Safety Inspector deams that the boat is not safe it cannot race in competition. Simple rule!