: I have now placed "outriggers" with strings on each side of the boat
Scott,
Now, I'm not a hundred percent clear how you've got this rigged, it sounds like you've adapted winding sticks to form alignment. This is a traditional method for determining if a plank's surface is true. A straight "stick", usually a 3/4 by 3/4" length of wood, that's about three times the width of the plank is placed at each end. By sighting over the two sticks the amount of twist in the plank can be easily seen. As the twist is planed out the sticks can be used to check your progress. As mentioned by others the twist is easier to see because the sticks multiply its visual effect.

I'm not sure why you would need the strings. you should be able to sight down your outriggers and clearly see any form which has its DWL twisted. Only problem I see is that the outriggers will have to be rigged every time you want to check alignment. And don't forget you want your center lines all centered. Perhaps that's the purpose of your string?