Rolf,

this rule is in both the F16 and F18 rules in some form or another. One option I've seen used is a water tight bulkhead at the forward beam. with a screw in (transom style) bung in the base. This creates a watertight compartment forward of the beam and the bung is released through an inspection port when the boat is on shore. As you're probably aware most people get around this rule using foam.