Striking Intersection between Antifouling and Topsides Paint

[The Froon]

I am ready to strike a new line marking the transition from antifouling paint to topsides paint, and will later come back for a boottop as well. I plan on using a method described by Tim in the re-striking of his lines on Glissando. I will create two structures, both astern and at the bow with a horizontal crossbar set at level. I will then run string for and aft, weighted, in order to tape and mark the new line.

Here's my dilemma. I understand that the boat need not be level for and aft, but only requires it be level port rail to starboard rail. However, my Sea Sprite is not sitting on a level surface, and I am not sure I have the boat sitting level as it would appear on the water. There is the faint outline of the prior line, and my thought was to begin at the bow using this old line, and then run the string toward the stern making sure it stays level. But if the bow is oriented downward, will not the string produce a line that is "falling" downwards as it moves toward the stern. It seems to me that I need to find level both amidship and stem to stern.

Any ideas?

Thanks,

Brian

[Hirilondë]

I would think for this to work not only does the boat need to be level on both axes, but the 2 wooden structures need be at the exact same altitude as the desired water line or at least the same altitude as each other and used as an offset reference. If not, then there is something I don't understand at all. I use an old style surveyors transit, which is just a slightly more sophisticated way of doing what you seem to be describing. If I didn't already own it I would do it in a fashion like you describe.