The Hull

5.1 Materials and methods of construction are not restricted except as provided by these Rules. The designer’s drawings show a method of constructing in moulded plywood.

5.2 Hull Shape

5.2.1 The hull shape shall conform to the designer’s drawings and the offsets annexed within the tolerances specified by the measurement diagrams and these Rules.

5.2.2 Hull moulds shall be checked by reference to plugs, moulds and production hulls before general use and after any modifications. Any builder constructing a new mould shall inform the International Association that it conforms to these Rules. The International Association may check moulds at any time.

5.2.3 Station 11 is defined as the plane at right angles to the base line shown in the measurement diagram and passing through the aftermost point of the hull, excluding rudder fittings. The hull datum point is the point on the hull centreplane where the outer surface of the keel band would, if projected, intersect Station 11, ignoring any actual rounding of the keel band. Other measurement stations are planes parallel to Station 11 at the specified distance from it.

5.2.4 No part of the after edge of the hull shall be more than 7.5mm from Station 11. No part of the after end of the seat-tank shall be more than 20mm forward of the after edge of the hull. The design of the transom is free in other respects.

5.3 Keel Band

5.3.1 Along the centreline from stem to transom a flat keel-band shall project not less than 3mm and not more than 4.5mm from the surface of the hull (with keelband removed) and may be rounded to a radius of not more than 3mm. At the sides of the centreboard slot the section may be ‘half-round’ instead of flat.
Keel band widths shall be within the following limits:

min (mm) max (mm)
Transom 30 75
Station 9 65 75
Station 6 65 75
Station 3 25 35

Forward of Station 3 the keel band may be faired into the hull.

5.4 Foredeck

5.4.1 The after edge of the foredeck (which need not be straight between the centreline and the gunwale) shall lie within the tolerances set out in the Measurement Diagram. The after edge of the foredeck at any point along its length shall be at or above the “top of gunwale”. The “top of gunwale” is defined as being a point 20mm inside the extreme edge of the hull regardless of construction.

5.4.2 Forward of the most forward position of the after edge of the foredeck the only apertures permitted are:

  • Spinnaker chute
  • A combined area of not more than 5000 mm2 for rigging and controls
  • One or two areas not exceeding 120,000 mm2 each, no part of which shall be further than 3486mm from Station 11, or within 100mm of the hull centreplane, or within 250mm of the “top of gunwale”.

5.5 Forward Watertight Compartments and Seat-Tanks

5.5.1 The forward compartment and the seat-tanks shall be separate watertight compartments.

5.5.2 The watertight bulkhead and seat-tanks shall conform to the drawings within the tolerances specified in the Measurement Diagram.

5.5.3 The forward compartment may include one spinnaker chute only, the volume of which shall not exceed 20% of the total volume of the
forward compartment. The construction of the spinnaker chute shall not impair the watertight integrity of the forward compartment.

5.5.4 The watertight diagonal bulkheads at the forward ends of the seattanks shall lie at or forward of the after edge of the foredeck.

5.6 Centreboard Case and Thwarts

5.6.1 The internal dimensions of the centreboard case shall conform to the tolerances specified in the Measurement Diagram. No temporary or movable insert in the centreboard case is permitted. (CLARIFICATION OF RULE 5.6.1)

5.6.3 Thwarts or other stiffening or reinforcing members may be fitted across the hull within 3581mm of Station 11. These members shall not be constructed in such a manner as to form a second cockpit floor or an additional buoyancy chamber.