1. Would a hull with an open central section of the aft overhang (fig 1), extending from the transom forward to a short distance aft of the aft waterline ending, comply with the class rules?
2. Does the presence of a deck across the top of and joining the twin overhangs (fig 2) make any difference?
3. Does the width of the open section (fig 3) make any difference?
4. Does leaving the twin overhangs un-decked (i.e. each is no more than just the thin skin of the primary hull moulding) (fig 5) make any difference?

1. No. The open section is a hollow in the surface of the hull (see definition of hollow below). Since hollows in the external surface of the hull are prohibited less than 40mm above the datum waterplane and more than 15 mm from the centreplane, the proposed feature clearly falls outside the rule D 2.4(b) and the hull does not comply with the class rules.
   Hollow is undefined in CR, ERS and RRS. The Oxford English Dictionary definition of the noun ‘hollow’ is: “a hole or depression in something”.
2. No. The presence of a deck does not change the presence of hollows in the external surface of the hull to be tested under D 2.4 (b).
3. Yes. D 2.4(b) (3) makes an exception for hollows within 15mm of the centreplane which are permitted. The reason for this exception is to permit the hollows that are formed by the presence of the keel and rudder where they join, or are faired into, the hull. If the hollows are entirely within this region they are permitted.
4. No. In this arrangement the upper surface of the overhangs are “inset transom and upper surface of deck” and thereby, any concavity in that upper surface is not prohibited by D2.4(b) 5).
   The absence of a deck or any other structure apart from the hull shell does not change the presence of hollows in the external surface of the hull to be tested under D 2.4 (b).

The 2002 CR have the same effect.