Makoto Uematsu requested Farr Yacht Design create the best Transpac 52 to compete in a broad mix of venues including both course and distance races. Design 533 is our answer to the design brief. Within the bounds of the otherwise tightly controlled Transpac 52 rule there is some room to set the balance between upwind and downwind performance. Displacement and VCG are limits set by the Transpac 52 rule so we were left to choose the optimum beam to draft ratio to produce optimum upwind and reaching power versus downwind slipperiness. While the overall length of the boat is set by rule we were free to optimize the waterline length and shape details to best suit the boat's expected race schedule.
To determine the optimum hull characteristics FYD conducted a research program employing a combination of VPP studies and computational fluid dynamics experiments. We developed a series of candidate designs to explore the available rule space. The performance predictions for each of these designs were then combined with wind distributions for the various targeted races to determine the optimum hull parameters and the consequences of being off optimum.
This research program addressed the following principal areas:
- Selection of optimum beam waterline.
- Maximum beam and hull flare effects examining the trade-off between heeled drag and increased crew righting arm.
- Selection of displacement within rule range.
- Effects of being above rule VCG.
- Transom immersion and effective length.
- Forward section shaping to improve the onset of planing and boat handling in waves.
- Appendage size refinement and optimization for particular event priorities offshore versus around the buoys etc.
- Bulb shaping and style for particular event priorities.
Hull
We have chosen the beam waterline to give the boat exceptional upwind and reaching speed. We have carefully crafted a beautifully fair hull shape, a by-product of the freedom of the box rule format, to minimize the wetted surface that accompanies higher beam. Crew weight supplies a significant proportion of the overall righting moment so the hull exhibits a close to rule maximum beam at the deck. For Design 533 we have examined the average boat speed profiles for a series of events and built upon our extensive knowledge base in this area to select an appropriate level of transom immersion in sailing conditions that we feel balances the competing demands of round the buoys racing and high speed offshore sailing. The waterline is maximized at the bow leaving just enough distance to the upright stem to fit a reasonable knuckle radius.
Appendage Geometry & Sizing
There is a wide range of freedom in the design of the appendages. Within the restrictions of overall draft, permitted materials, and minimum keel fin strength we were free to develop low drag, good handling solutions. The rudder was sized to provide sufficient lift and good handling characteristics with minimal area and drag. The combination of optimized planform shape and our own foil sections, designed in-house, produce a high lift/low drag rudder that gives the helmsman plenty of warning of an imminent stall. The keel fin was sized to provide sufficient lifting area for starting and other maneuvering situations while balancing the competing concerns of upwind and downwind sailing.
The bulb concept for Design 533 also reflects efforts to balance upwind sailing and maneuvering issues with the desire to minimize viscous drag. We chose a chined bulb shape to improve the upwind performance and achieve the deepest center of gravity. The bulb shape was optimized using our understanding of transitional flow mechanics that contributes to reducing the bulb viscous drag.
Deck Geometry and Layout
The deck geometry combines the minimalist coach roof and flattish deck camber of our previous design work with an aggressive cockpit aimed to position crew not hiking as far outboard as possible. Substantial weight savings have beenachieved in the aft cockpit by continuing the cockpit sole out to the hull, thereby eliminating the cockpit sides. The cockpit sole has been sloped down aft of the traveller to minimize its surface area while enhancing its draining properties. Our vertical transom style has been maintained to position the topmast backstay fittings as far aft as possible, minimizing the mainsail roach and topmast backstay interaction.
Advances in the deck layout are focused on a winch system designed for forestay-less gibing, where two after guys are required to be loaded throughout the maneuver. In this case, the secondary winches, by careful positioning can be used for after guys downwind and topmast backstay upwind. The mainsheet system is a 2:1 "half German" style system led aft to a single pedestal driven winch on centerline. The mainsheet grinder pedestal and primary pedestal are linked below deck to provide maximum horsepower during highly loaded maneuvers.
Hydraulic tensioning systems are in place for both forestay and "code 0" tack line. These systems both utilize through deck sheaves and below deck strops intended to position the actual hydraulic cylinders as far aft and low in the boat as reasonable possible.
Longitudinal jib tracks are combined with in-hauler systems to provide ample sheeting range along side the relatively large class required coach roof. Mainsheet traveller and other control lines are led below deck to maintain clutter free deck space.
Rig
The fairly standard 20-degree swept spreader rig has been combined a cathedral style topmast stay system to support "code 0" style upwind spinnakers. In this case the combined stay envelope has been carefully optimized to allow close sheeting of those sails.
The mast has been designed to class rule minimum weight and VCG targets. Where possible, IMS friendly mast and boom dimensions have been pursued to help ensure that the yacht can be competitive in other outside class events.
PHOTOS Click to enlarge.