Stability has to be a 'built in' attribute if a water-speed contender is to be both safe and successful. The craft's shape and weight distribution must be very carefully worked out long in advance of construction. To help define and then refine the shape of the Quicksilver craft, the team has undertaken extensive testing of scale models in windtunnels and on water, combined with various computer-based studies.
We have conceived a boat that is going to travel at aircraft speeds. It is still undeniably a boat, but the forces acting upon Quicksilver at extremely high speeds will, to a very large extent, be the same forces an aircraft is subject to and must cope with – aerodynamic forces generated by the airflow interacting with the craft. Once Quicksilver has accelerated up onto her planing surfaces, she will have very little contact with the water. She will be surrounded almost entirely by air.
The behaviour of the air as it interacts with our boat has a far greater influence than is the case with slower, more conventional boats – due to the fact that Quicksilver is designed to be the fastest boat ever built, and the faster the speed, the greater the aerodynamic influence.
When designing any machine that is going to travel at high speed – whether it is a road-going car, a racing car, a truck, a locomotive, a powerboat, or an out-and-out speed machine like Quicksilver – it is safer, more economical and plain engineering good-sense to test the concept in a windtunnel before committing to building the real thing.
The concept’s shape is a crucial factor governing its performance, but so too is its weight and weight-distribution. Stability, speed, safety; all derive from the combination of those three influencing factors.
Windtunnel testing tends to be a process of trial and error, but guided by the established principles of aerodynamics. And there is always something new to learn. The test data Quicksilver’s designers have been particularly interested in pertain to lift (you don’t want to the boat to become airborne or to run too lightly on the water), drag (because poor streamlining limits the craft’s acceleration and ultimate speed), and pitching moment (that’s any tendency – to be avoided at all costs – for the boat to flip over backwards).
Quicksilver’s windtunnel testing has involved placing scale models representing a variety of different craft concepts in two facilities at opposite ends of England. Initially, our wind-tunnel testing was undertaken at the University of Southampton and the models ranged in size from one-eighth-scale up to one-fifth-scale. The windtunnel used in many of those tests had a 'moving ground' floor to simulate the presence of the water's surface passing beneath the craft. More recently, Quicksilver's windtunnel testing has taken place at the University of Salford, using a one-tenth-scale model kindly manufactured for the team by the Innov8es company.
In the case of both the University of Southampton and the University of Salford, our research has been a collaborative effort involving undergraduates working side-by-side with Quicksilver’s designers.
Our craft, being built today, is the result of a total of almost 50 days of research conducted in the two windtunnels.
The original concept, and other early concepts that superseded it, sprang from ideas put forward by the late Ken Norris, who had gained enormous knowledge and experience co-designing (with his brother Lewis) Donald Campbell's famous Bluebird cars and boats in the 1950s and '60s. Efforts on these earlier concepts were, however, abandoned following difficulties encountered with their technical viability. The decision was taken to relieve Ken of his design-leadership role, and later – in the 2005-2007 timeframe – with new engineers joining our team to augment the original members, a design was arrived at which everybody involved felt entirely happy with.
Despite Ken failing to reach clear conclusions, the fact remains that his contribution was of inestimable value to the process of eventually determining a definitive configuration. Indeed, many of the key tenets of Ken's approach to achieving ultra-high speeds on water are embodied in the craft that is under construction today. His wisdom has proved to be a guiding light.
Back to the present, particular praise is due to our chief aerodynamicist, Mike Green, for guiding the conceptual design project to a successful conclusion. Mike was formerly the chief aerodynamicist at British Aerospace's Woodford, Cheshire, facility. He joined the Quicksilver team in 2005.
The team is also grateful to Dr Thurai Rahulan of Salford University for his ongoing role in our aerodynamic research programme.
Test activities of the past cannot be ignored, for they provided the body of research which is the Quicksilver project's foundation stone. We gratefully acknowledge the enormous contribution made in the early stages by the late Ken Burgin, Dr. Norman Pratt and Dr. Graham Roberts, all of the University of Southampton. Early progress would not have been possible without John Shinton, Stuart Delf, the late Brian Ball and the late Ron Earwicker, who created scale models of the initial (Ken Norris-inspired) craft configurations that we assessed in the windtunnel.
The colourful side of testing and analysis is demonstrated by the computer-generated image above. Data of this type has been used to perfect the shape of Quicksilver's engine air-intake. The image reveals the distribution of airflow into the compressor face of the engine, as measured by an array of 36 pressure-tapping probes linked to a transducer installed within a fifth-scale windtunnel model during simulated record runs. One of the probes has failed to function on this run: hence there are only 35 reference-point crosses on this particular read-out.
Just as Quicksilver's aerodynamic performance has been refined by windtunnel tests, so the hydrodynamic performance has been refined by water-tank towing tests and by testing free-running models operated by radio control. Not only the current shape, but also other completely different shapes, were tested over the years. For example, an intensive series of waterborne tests of a reverse four-pointer concept was conducted with a one-eighth-scale model in the quarter-mile-long towing tank at the Centre for Marine Technology at Haslar, near Portsmouth.
Thanks are due to the late Bo Johannson, and to Bruce White, for making some of the waterborne models that were tested.
Weight-watching is of crucial importance, and a constant preoccupation, in the designing and building of an ultra-high-speed craft such as Quicksilver. If the boat becomes too heavy, or if its weight is distributed incorrectly, it simply will not perform as intended.
So, in addition to the aerodynamic and hydrodynamic work outlined above, structural analysis and testing at the conceptual design stage of the boat as a whole, and thereafter in the detailed design of its individual constituent components, are vital to the process of fully optimising performance.
There is a fundamental challenge to this, in that whilst great efforts are made to keep the weight of the boat to the minimum, it is necessary at the same time to maximise its strength and rigidity, or it will flex excessively when it runs at speed on the water and at best under-perform, and at worst be downright dangerous. The inherent challenge is that, whilst it is relatively easy to make a structure strong, it is a good deal more difficult to make it both strong and light.
So what are the consequences if the boat was allowed to become overweight? There are two main risks. First, there might be a problem getting the boat to rise up onto its planing surfaces at the start of each run; second, an overweight condition would in any case result in the boat being unduly sluggish under acceleration, as well as slow to retard at the end of a run.
Putting it in a nutshell, an overweight condition reduces performance by slowing acceleration and deceleration. It saps the boat's potential.
With a limited length of lake available, and with fuel at a premium because a bigger fuel-load represents a major weight penalty, poor acceleration and deceleration performance are not to be tolerated unless it becomes absolutely unavoidable.
There has been extensive use of finite-element analysis (FEA) techniques throughout the design of Quicksilver. The colour-coded image shown above is one of many hundreds that have been generated by the design team's FEA work.
To facilitate FEA, as well as other CAE processes, Quicksilver's design is enshrined in full 3D CAD. We are highly fortunate in having PTC as a long-term collaborator on our project, and we have long made extensive use of PTC's Pro/ENGINEER Wildfire CAD software and other CAD/CAE products.
The front view of Quicksilver shown above is a product of the ongoing CAE work being done by the team as the process of detailed design and build of individual hull components steadily continues. The diagonal struts, which contribute strength and stiffness in the attachment of the sponsons to the main hull in a trade-off with the horizontal sponson-arms, are a relatively recent addition. They were introduced as part of a set of enhancements to overall structural efficiency, which is always a trade-off between weight, strength and stiffness.
Having decided that the addition of the diagonal struts creates a more optimal hull-to-sponson geometry, the team intends during the course of 2012 to windtunnel test a one-tenth-scale model with struts fitted, to assess their influence on aerodynamic performance.