Marking the Waterline

I knew where it had to be at the bow and the stern, the challenge is to connect these points up in a straight line on a curved surface.Prior to painting the hull, we need to know where the waterline will be: above the waterline is a gloss paint, and below the waterline is an antifoul paint. The position of the waterline is given in the plans, and I had it laser-marked on the steel plate when I had the steel cut. So I knew where it had to be at the bow (front) and the stern (back); I also had a mark on each side in the middle of the boat. The challenge then was to connect these points up in a straight line on a curved surface.

There are a number of ways of doing this, and I chose to use a string line after seeking advise from Greg the shipwright guru from Brisbane. This was quite simple to do:

  • level the boat.
  • place a piece of timber (wider than the boat) across the bow, at the same height as the waterline and perfectly level.
  • similarly, place a piece of timber across the stern.
  • stretch a string line between the two pieces of timber, so that it is just touching the hull, tape the string to the hull.
  • pick an end and start moving the string line along the piece of wood into the hull and keep taping the string. If the taped points are too far apart the string will roll down the hull giving an uneven line.
  • Once one end is done, do the other end.
  • With the side completed, apply masking tape along the string line and remove the string line.
  • Do the other side and transom in the same way.

On the first side, we had two goes at doing the string line before we were happy with the result. See the photos below.

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