Left/above: the all-conquering Dead Cat Bounce N12 design with which Jo Richards marked his return to the class in 2009 more than 30 years after last winning the national crown. In the hands of Jo and Sophie Mackley the original Dead Cat won six out of seven races at that year’s championships. Different variants of the design have since been built in both wood and composite and it is still one of the most reliable all-round performers, winning more titles during the intervening period. The design features lots of rocker with a small bustle with the waterline pinched in towards the transom, lost buoyancy replaced by use of a generous rudder foil, the rudder/foil mechanism canting using the adjustable piston controlled from the helm on which the lower rose-joint pintle is mounted
various attempts to improve them. All the variables have been explored: wing section, amount of sweep back, amount of dihedral and vertical position. Some com- puter modelling has been conducted which suggests that positioning the wings as close to the surface as possible is optimum. The problem with placing the wings
close to the surface on a dinghy is heel – as soon as a wing comes out of the water ventilation occurs and the boat noticeably slows. So the trick appears to be to posi- tion the wings as close to the surface as possible without them breaking the surface under normal sailing conditions, then have just enough sweep back to help any weed naturally slide off and finally as little dihedral as possible.
Sailing technique The National 12 has always been a respon- sive boat, reacting well to crew movement and able to turn on a sixpence. The winged rudder altered that: when first stepping into the DCB, tacking was noticeably slower, the problem being the wings acting as a brake. A much slower tack is required with a smooth roll so that the wings continue to move forwards through the water and don’t create turbulence. If the boat is brought upright too quickly after a tack
then the flow detaches from the wings, causing turbulence and slowing the boat. A similar technique applies to the gybe.
A sharp gybe can result in the wings stalling, slowing the boat, adding pressure to the rig and making the gybe harder. On the other hand, in a smooth gybe the wings are beneficial as they stabilise the boat and keep the bow out of the water.
New designs Shortly after the DCB was released Gavin Willis developed his Paradigm 3 design which also sported a minimum sheerline, with the main objective being to reduce windage and maximise righting moment. His first Paradigm was maximum height which got the rig higher and into better wind but with the downside that when the boat heels the righting moment from the crew is lost very quickly. Two years after the Paradigm 3 Dave
Hollom (well known to readers of this magazine) took a characteristically fresh approach with his Hijack design. The Hijack had a fuller bow, V-shaped mid- sections and a wide transom as well as a winged rudder. The Hijack proved very fast in strong
winds and in the right conditions faster than the DCB, but didn’t appear to be
quite as good all round, probably due to the fuller sections and greater wetted surface that affect the light-wind performance.
Paradigm 4 – shape shifter Gavin Willis in his latest 2019 design has also introduced a concept to change the hull shape while sailing, minimising wetted surface area for light winds and adjusting to flatter planing sections when the wind increases. The target is to be able to match or beat the Hijack in heavy air and take on the DCB in the light to moderate winds. The mechanisms in the boat look quite involved and to many it is a surprise that the imple- mentation actually works – hence the first Paradigm 4 is appropriately named Really?. Graham Cam
Gavin Willis – Paradigm 4 designer Seahorse: how did you originally identify this as an idea worth pursuing? Gavin Willis: I spend a great deal of time travelling around the country designing dental practices. This gives me lots of time for free thinking – I even surprise myself sometimes with what I come up with… Every day I ask myself, ‘What, if I could
do it, would make a fundamental differ- ence to the way things are done and how can it benefit the project that I am working
SEAHORSE 57
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