The Diode 36 was engineered in response to several key guidelines; she had to be lightweight (4320 pounds lightship), stiff, relatively inexpensive, and simple to build - requirements that do not at first appear very different from any sportboat - but throw in the lifting / gybing high-aspect carbon keel and 2000 pound bulb and matters get trickier! Structure was to be efficient and of course true to its function - it was essential to visualize the boat as a skiff or performance dinghy first and foremost.

The global goal was to make our keel perform the same function as a gybing centerboard, and so we looked often at the 505 dinghy, which can be built with a gybing centerboard, for ideas and inspiration. Centerboards, being unballasted, can be shaped to automatically rotate to windward by designing a pivot point within the trunk aft of the centerboard's center of lift - tack and the board flips over to the new side. We knew we would never be able to depend on a ballasted keel to gybe automatically, and we desired a range of adjustability - so after several design iterations set the keel in fiberglass drums extending from hull bottom to cockpit sole. A rotating inner drum contains the fin itself and is supported on two Ertalyte (PET-P plastic with excellent wear resistance, a low coefficient of friction, high strength) bearings within the fixed outer drum. The inner drum is retained by a flange resting on an Orkot (low friction composite) thrust bearing, and set up to be rotated by winch handles through port & starboard Antal line drivers leading to multiple purchase and then to the drum. The keel angle controls are located aft so that the skipper or main trimmer can play them. The keel turns easily and accurately when underway, and upwind we are seeing it perform exactly as anticipated, giving us speed with height.

A major benefit of using concentric drums to fix the keel is load distribution - even with the 9' draft, there is 25% bury to the fin cantilever which translates to manageable side loads taken to hull and cockpit sole, which did not have to be overly reinforced. Keel floors are also not required, keeping weight down. Forward of the mast is a delta bulkhead, spanning out to the composite chainplates - such structure is very efficient as it performs several functions; handling mast compression and inboard shroud tension, distributing the keel's racking loads on the hull, and framing the forward edge of the cockpit and side tanks.

Keeping weight low and construction costs down emphasized the necessity for efficient use of materials and structure. In response we used a thick (1" A500 & A550 Core Cell) core in the hull (3/4" for deck and cockpit), with biaxial E-glass skins engineered to be as thin as possible while meeting ABS requirements for strength and stiffness. Internal structure of frames and stringers is minimized. There two frames forward of the delta bulkhead, the forwardmost aligned with the headstay. Aft of the keel drum are two frames. Due to the hull's thick core the only longitudinal structure are panels framing the outboard engine storage well aft of the keel drum, and small stringers forward under deck. The hull shape also contributes to the boat's efficiency. Soft form transitions everywhere eliminate stress concentrations. Unavoidable sharp transitions, such as the hull / deck joint, are radiused and cored to ease stress and maintain stiffness from panel to panel. Overall the boat is extremely stiff and plays upwind through waves with imperceptible shudder and zero fuss.

Ross Weene