Correct length?
Years ago Hobie Cat would add an inch or subtract an inch as people said the wires were long or short. There was no standard for the handle height. I decided to set the Hobie standard at 32 inches from the rail, wing, seat or what ever you are trapping from. That is an average height for me that gets the handle at just about shoulder height. Lower and you can't lift your butt off the rail to get out... higher and you can't reach the handle when trapezeing.
Really old wires have a large thimble hanging below the handle by about 1 1/2 feet. That was the original hook up point. Later we shortened the thimble to be directly below the handle and added the rope adjustments for trap height.
I have a 1980 bulletin that shows the trap wire finished length at 18' 1 1/2" (using the original long tail below the handle.) - The current guide shows 16' 9 1/8"