During a kite trip I had my centerlines snap…my fault for not keeping the sand off them. Got a couple years of heavy use
Anyway I needed new lines in a hurry, faster than I could order from Ocean Rodeo, and I found that you can make a centreline out of high quality sailing rope.
Used samson high test line, 9500 lb functional load capacity. Should do the trick. Looked and feels exactly like OR but its a cool blue color.