Draw a 90 degree cross on a piece of paper large enough to accommodate a whole kite. Neatness counts. I like to use a fine tipped pen. Once through, both directions.
( Bamboo ) All bamboo bows are shaped differently making your template a "one off". The piece of paper you are using -will- be the template. A one shot deal.
( Synthetics ) Carbon fiber rod and similar materials are reliable insomuch as very consistent repeatable bows are possible. Two (or more) like lengths and diameters bent to the same distance (straight line) tip to tip deliver copy after copy. The finished paper template can be transferred to a more permanent material to be reused.
( Bamboo ) Bend the bow to the desired shape and secure it with a piece of thread at the tips. If loops are tied at either end of the thread it is only necessary to larks head them on to the ends of bow. If the thread slips, dab on a little rubber cement so it holds.
( Synthetics ) Bend the bow to the desired shape and secure it using a piece of music wire. The wire should have small loops at either end. Tape over any sharp spots. Sand down the tips of the rod to points so they spring into the loop ends. Don't let the bow boink out of the fixture either. You do not want the rod with it's sharp ends winging about the shop.
O.K. Now we have a cross drawn on a piece of paper, a bow sprung into our thread (jig) or wire (fixture) and a spine cut to length.
One of the lines on the paper represents a line from tip to tip on the bow. The other or perpendicular line must be bisect the bow. This is the spine line.
Measure the exact distance of the bow, tip to tip and divide by two. I like to bisect from a friendly hatch mark on the meter stick so I have a center reference point. I lay the meter stick center reference point on the spine line of the cross. Then it is only a matter of measuring out away from the spine line to the correct half distance on the bow line. Measure it both ways and carefully mark it. Re-measure. Set the bow on the paper so the tips are up to and touching the line and the marks on both sides. Perfect.
Now that you are confident the bow is centered on it's line and marks, pick it up and dab a little rubber cement on it. Let it get slightly tacky. Before it dries, reposition the bow on the paper and let set till it will not slide around.
Trace along the outside of the curved bow with a fine tipped pen. It is only necessary trace half of the bow shape. From the spine line to the bow tip. Don't let the dumb end of the pen sway around like a bad static kite or your line will not trace the bow accurately. Remove the bow from the paper.
( Bamboo ) Mark the bow so you will not forget which side is up. Leave it sprung in the jig and set it in a place it where it will not be disturbed.
( Synthetics ) Leave the bow sprung in the fixture and set it in a place where it will not be disturbed.
The paper now has a cross drawn on it and is marked on both sides of the bow line. Half the bow curve is drawn from nose to bow line mark.
Position the spine on it's line and mark on the paper where you want the nose and tail.
Draw a line from the nose to an area where you want the sail to intersect with the bow.
Draw a line from the tail to the mark on the bow line.
Doubled edges, wingtip pockets or any folds must now be added to the drawing. If you want part of the bow to have a folded piece of sail material over it, position the bow off set from the curved line trace appropriately.
I like to cut the paper template out with an X-ACTO knife and a straight edge wherever possible. From nose to tail, from nose to curved bow line, from tail to wing tip, the wingtip flaps and then I fake it on the curved areas.