When it was finished, this was the business. Wood and steel, cant go wrong. Ive used it loads of times, solid as rock.
[Added]In use: It takes 5 mins to load the windsurfer and is stable at 60mph, which is the fastest Ive gone.
Step 1: List of Materials/Cost/Tools/Time
Total construction time : 1.5 days. It took me about 8hrs actual work time, but I needed to let glue and paint dry
Step 2: Cutting wood
I made sure that the length of the wood allowed it to sit in the back of the car when not in use. Although you could leave it on the roof when windsurfing.
Step 3: Getting the Curves
So using a bit of scrap wood and a marker, get the shape of the roof - see the picture. Suggest you mark the front, it can get confusing otherwise.
Next you need to curve the ends, I used my coffee cup that just happened to match the curve I needed. Draw round your mug (the cup, not your face!)
You only have to do this once, the second wooden runner is cut from the first.