I researched the subject on the Internet, the Cobra Club Forum and read an article by Paul Hutton (which is really good) in the April 2017 publication of the Snake Torque magazine. From this research I reckoned that there was a way of cutting down the draught on my neck and my passenger's without detracting from the Cobra's lines. So here is what I have done.
First the four seat belt eye bolt anchorages were unscrewed from the roll hoops. The wind deflector will fit behind the seats and onto the face of the hoops. Masking tape was applied to the body on the cabin side of the roll hoops to prevent any marks.
|Eye bolts removed and masking tape applied|
|Duct tape on back to hold template|
|Hardboard with first line drawn|
Then I marked up a slope - from the top middle of each roll hoop to the outside (about 75mm down from the top), before marking rounded corners. The top corners were a 75mm radius and the bottom corners a 25mm radius (hope this will be ok for the hood or hardtop I get). The template was then cut with a jig saw and planed to get smooth edges. Next I marked the eye bolt holes using a hammer against the hardboard and the mounting hole. The centre was then marked and drilled using a 6mm bit. After checking the holes were in the right place, I drilled them out to 22mm using a step drill. The hole needs to be big enough to clear the shoulder of the eye bolt.
|Template cut and eye bolt holes drilled|
|Final template with eye bolts in place|
Laminated glass - this option was beyond my capabilities to work with. It would need to be laminated to avoid it shattering if hit by a stone. Glass is expensive, not easy to cut or drill and is also quite heavy. So this was ruled out.
Perspex - easy to cut and drill. Cheap to buy and widely available. Loses transparency over time, can warp when exposed to UV light and can break in to large shards if hit by a stone. So this too was not an option for an open sports car with no top.
Acrylic sheet - easy to cut and drill. Stable dimensionally, to UV light and stays clear. It has greater break resistance than glass. On impact it breaks in to relatively large pieces, rather than small pieces or shards. Withstands large changes in temperature. Lightweight. Better transparency than glass. Expensive and harder to source.
Solid polycarbonate - similar properties and strength to acrylic sheet. Easier to source and less expensive than Acrylic.
So polycarbonate it was. I have ordered 8mm thick which by all accounts is about right. Any thinner and I risked it vibrating or flexing at speed. Any thicker and it is over doing things. The size of the polycarbonate sheet ordered is 1220mm x 360mm. Prices seem to vary quite alot over time (oil prices?), but Century Plastics in Sheffield seemed to have the best price at around £30 including VAT and carriage and their service is great.
My next post will be cutting, drilling and fitting the deflector.