|Virtual Javelin - Part I|
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This article describing Javelin Design82 by David Lee as printed in Sailing New Zealand magazine April 2000.
Javelin Design Innovation
- Part I
To measure the speed differences between the current designs as well as any new design a performance estimation programme was developed. This programme is based on experimental work carried out at the Delft University of Technology in the Netherlands. The work at Delft involved the systematic variation of different hull parameters such as prismatic coefficient, length to displacement ratio, centre of buoyancy, etc to determine their effect on hull drag. This work is the foundation of many velocity prediction programs used by yacht designers.
Once the programme was developed, analysis was performed on the currently successful McNeill, Stacey and Salthouse designs to establish a design benchmark A number of new designs were developed in different corners of the Javelin class rules and run through the programme. The results showed that hulls with a very fine entry, minimum beam, maximum rise from keel to chine at mid-length and a minimum width stern gave the least drag. Experience in the class found that very narrow sterns tend to cause downhill control difficulties due to the swept in flow exiting the hull. The effect of rocker in the design was to decrease drag at low speed by reducing the wetted surface area. However, reducing wetted surface area via increased rocker comes at the cost of planing performance. It was found that wetted surface area could be effectively reduced by increased section curvature in the aft of the hull. An added bonus of doing this was that the aft waterlines could be straightened while still keeping the stern reasonably narrow. From these ideas the design was refined with the help of 3D graphics and CNC machined 1/5th-scale polystyrene models to visualise the actual hull shape.
Not surprisingly the design to many in the class looks like a combination of the McNeill, Stacey 95 and Barn Mk II designs. The design takes the high forward chine from the Stacey, the minimum beam from the Barn and the flat aft sections from the McNeill. The design has reduced both wetted surface area and wave making drag by 5% over the current designs. It also has significantly finer bow sections than previous designs allowing easy chop penetration.
With the upcoming South Pacific's at Wellington this Christmas it is anticipated that at least four hulls to the design will be built over the winter in an attempt to regain the title that Australia has won at the last three contests.
Another class innovation will allow the design and building programme to be followed on the Internet. The Javelin Association website, www.javelins.org, will be showing progress reports, photographs, costs and construction details "as it happens".
Sailing New Zealand will also be following the project to the water with a series of articles in upcoming issues.