---

Why don't you try the common-sense method?

1) Put on a bathing suit or shorts.
2) launch or moor your boat in a lake or shallow area about waist deep in a location where you can walk on the bottom all the way around the boat and the water is calm.
3) secure your boat by anchor or mooring lines.
4) get in the water.
5) use a sharpie and make marks, ( I make dots), at the water level that are close enough together to allow you to use a straightedge later to pencil your lines for the bottom paint.
6) Remove your boat from the water, take it home, straightedge the marks with a pencil or chalkline, paint the bottom in the perfect place. This will be to about 1" above the water line all the way around the boat.

Sometimes, what I am really puzzled about is why folks don't seem to think about what they are doing. I do agree it is much easier to complain that somehow this complete lack of thought is somehow the fault of the boat manufacturer, but then I might have to move further west or north.