The Owner, George 'Dooie' Isdale's brief for the "Diode 36" was initially for a One Design concept:

1. Design a '32 foot boat with a 4 foot bow,' from which to fly an asymmetrical spinnaker and code-0, thus avoiding the weight, complexity & expense of a reciprocating sprit.
2. Incorporate a rotating keel. Oh, and it must lift to get to yacht club hoists and to go on a trailer. Beam must be under 11 feet (it is 10' 11") so it can be towed in the US without an escort. (You still need permits.) Lifting rudder for the same reason.
3. No rules. This is a 'One Design' or PHRF speed machine for racing in protected waters.
4. 4-5 Crew; legs inboard (a la Etchells, a class which, amongst other successful One-Designs, Mr. Isdale instigated)
5. Stiff with above crew, slippery in light air, and sport-boat planing ability

The last of these requirements, and the beam allowance, governed design and shaping and provided the kind of challenge that keeps one designing boats, while the rotating, lifting keel provided a real challenge for an engineer. (See design-engineer Ross Weene's separate piece on "Engineering & Construction")

With the rig set so far back in the boat because of the extended bow, we wanted to ensure that the boat would tack and balance well, so a 60 inch long radio-controlled model was built, with a channel for the rotating keel. The boat balanced, tacked & tracked superbly and gave us confidence (and great fun!) to refine the concept full size.

Hull shape: The waterplane is very narrow for a planing boat, and there is great flare in the topsides to keep the limited crew as far outboard as the beam limit allows. The keel-aft position dictated by moving the headstay aft forces a serendipitous far-aft placement of the Longitudinal Centre of Buoyancy (LCB) to a position favouring high-prismatic, upright, planing shapes. (Prismatic coefficient defines relative fullness or fineness in the ends of the immersed hull). Conversely, upwind prismatic coefficient is reduced (as is favourable) by moving crew forward when the boat is heeled. This hull has much more rocker than we would use in, say, an Open Class design, as this boat is really our first designed for Windward/Leeward racing and, apart from the control over fore-and-aft trim, we wanted to ensure she would turn quickly. When the hull is upright, the ends are well out of the water; when the boat is heeled, upwind, the forefoot 'rolls-in' giving the bow enough bite to resist its being blown to leeward. Similarly, when the spinnaker is up, the bow rises keeping the forefoot well clear of the water, the prismatic high and the rudder well-immersed. The high rocker would also allow the boat to slide more easily 'off-axis' off the wind with the keel down to leeward a couple of degrees!

Most importantly, in the endless variables of heeled behavior we studied in the lines-development phase, we carefully sculpted the upwind heeled waterlines to keep the heeled canoebody symmetrical, and no more than about 5 degrees off the centerline. (See attached drawing "Heeled Waterlines") This 'drag-couple' (now-now!) of the heeled hull's directional desire against that of a fixed centreline keel has long perplexed and bothered me. Surely the ability to align the rotating keel closer to the longitudinal shape of the heeled waterline, allowing for leeway, would reduce drag for the lift provided from both keel and heeled hull? In the limited sailing we have done in the weeks since the Diode 36 has been launched we are seeing exceptional upwind speeds and angles for a superlight boat. Pointing with other IMS boats, Diode is sailing upwind at 7.2-7.3 knots, which is exceptional for a 36 foot sportboat type, and easily exceeding our own continuously refined VPP's. Off the wind, we have seen 15 in about 20 knots true, the most wind she has sailed in to date. And these are early days!
The owner & crew, including Ross Weene, design engineer from our office, are planning to take the Diode 36 to Key West Race Week in late January.

Rodger Martin, Newport RI, USA.