Thats Genious Danny!
I actually made it much harder on myself. I used the polyline tool and drew some back and forth zig zag polylines. Then I turned on control points and moved each side into the surface to intersect. I rotated the bottle 180 to get the seam for the other side snap. Then after projection I had a series of rings I trimmed down the middle and deleted the appropriate sections to get the helix. But the curve projection created some wierd stuff with this and required some extra editing to get my helix arcs cleaned up.



But your way is much simpler and precise!!