Design
For a boat with hot and cold-running everything, Phaedo pops a hull (below) with little encouragement and makes a fearsome match for raceboats like the Maxi 72s over an offshore course. The reduction in chord of her new and deeper foils (right) is evidenced by the ‘spacer’ that now fills her daggerboard slots. Nice lifting rudder foils (far right) complement shallow water access while the latest spar from Southern is both lighter than its predecessor and also boasts a lower VCG
seaway, and the rig wags fore and aft. This movement dramatically decreases the lift generated by the mainsail.
A fixed rig is typically lighter than a rotating rig with a lower vertical centre of gravity. Pitch amplitude is decreased by using a fixed rig, thus increasing aero - dynamic efficiency. Of course, a rotating rig increases aerodynamic efficiency by providing more favourable flow into the mainsail. So which solution offers the better efficiency? For Phaedo it was too close to call. The rig configuration split in the Imoca 60 fleet highlights how fixed and rotating rig solutions can converge in performance. In the end, Phaedo went with the simpler solution with fewer mov- ing parts. This also allowed the deck plan to be cleaned up and sailing operations to be simplified. The deck-stepped mast base executed by Southern Spars, featuring Winmar turning blocks, is a work of art. The single largest performance gain available to a stock Gunboat 66 is to replace the daggerboards. When the Gunboat line was originally conceived they were cruising boats first that occa- sionally participated in intermural racing. Gradually, the driven individuals who own these boats have demanded more perfor- mance. So the stock daggerboards that did not extend above the decks when retracted have gradually been replaced by longer daggerboards that feature reduced chord, thickness and drag. Both asymmetrical and symmetrical solutions had been designed and implemented prior to Phaedo’s refit. Given this previous experience, Lloyd Thornburg asked me to further optimise Phaedo’s appendage package.
46 SEAHORSE
The first step was to get the tools in order. We worked with Clay Oliver to calibrate his latest VPP software. I was also able to feed Clay live performance data from Slim while racing in the 2014 St Maarten Heineken regatta. This data, and Clay’s tireless development, have increased the accuracy of the WinDesign VPP for the entire Gunboat fleet and other new perfor- mance cruising catamarans currently under development.
We then created a Caribbean 600 race model within MatLab. This high-fidelity tool allowed me to input different VPP polar sets and ‘race’ the boats. Controls were established to change course condi- tions to simulate a wide range of ‘what if’ scenarios. With the tools in place three candidate daggerboards were created: S-Boards – designed to provide some downwind vertical lift while still maintaining upwind pointing (asymmetrical sections). C-Boards – primarily targeting offwind vertical lift (asymmetrical sections). Straight Boards – engineered to maximum possible span within the confines of the existing daggerboard cases. Targeting light-air upwind work (symmetrical sections).
Polars for each daggerboard set were loaded into the race model and the virtual Caribbean 600 was on! The results were fascinating as there were multiple lead changes around the course. Each option pulled to victory in different conditions. Overall the S-boards were the fastest, the C-boards were second and the straight boards were last. What was surprising was that the finishing times nevertheless fell
into a remarkably tight data cluster. The dock consensus that the Caribbean 600 is won or lost behind Guadeloupe was reflected in the race simulation. And in that situation it was always good to have the long, straight boards to get out of the hole. Armed with the results of the race model, all agreed that the straight boards offered the best value while producing the largest improvement on Phaedo’s weakest point of sail, upwind in light air. With the straight daggerboard decision made, the focus then shifted to executing the appendage details to the highest possible level. We contracted Nat Shaver to optimise foil sections for both the daggerboards and the new rudders. Nat was rolling off an intensive few years with the Emirates Team New Zealand America’s Cup challenge special- ising in foil development. During the Cup very specific programs were developed that allowed the team to save time and become much more efficient in pursuing the many and varied foil concepts tested. After the Cup ended it was clear that this sort of tool would be very useful for projects outside the Cup, saving time and therefore clients’ money while allowing a level of analysis not usually applied to those projects. Nat took it upon himself to develop a set of tools from scratch that work well for this sort of project, and the Phaedo refit was a perfect place to put these tools to work.
Built into the code is a lifting line and vortex lattice analysis to quickly analyse changes in the design. Using a quick analysis method such as a vortex lattice solution and taking advantage of the
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