The trick with the batten worked well but I needed something more flexible when marking out the tighter curves of the bow panels. I used a length of plastic overflow pipe I had lying about. I hooked a luggage elastic into one end and made a slit for the elastic in the other end. This enabled me to make an adjustable curve simply by pulling the elastic through the slit.
I then had a useful and inexpensive (free!) tool which did the job brilliantly!