I know this may sound too easy, but I would have thought that it would be meant to display on a 'level keel', so if you set the hull on the supplied base & posts, it would be in the correct plane to mark the waterline.
As it's all pre drilled, does it not just 'fit' together? I'm probably wide of the mark, but it's worth a try.
Some pic's may also help.
Edited By Kip Woods on 23/06/2018 21:10:55
Edited By Kip Woods on 23/06/2018 21:12:17