Older plans like the free plans we offer here, were drafted on paper. Despite the skills of the designers, they can not approach the accuracy of modern plans and calculations were not as elaborate. To build from those old plans, you must transfer the dimensions to wood or plywood, very often by lofting and correct some imprecision resulting from the scaling.
Many of the free plans show only dimensions for the molds or frames. Those dimensions are always given in reference from a baseline. Most of those dimensions are given inside the wooden planking but some like the stern and the keel, usually show the outside: pay attention.
Here is a link to some useful Bateau2 tutorials showing how to transfer lines from moderns plans to plywood: How to draw and cut a frame
How to draw a fair curve through points (Excerpt from our Stitch and Glue tutorial.)
Some of those older plans use a table of offsets.
A table of offsets is a table with rows and columns that shows the locations of points through which you will draw lines representing the hull of the boat.
You must mark points, draw lines full size on the floor and correct some inaccuracies resulting from the scaling: paper plans were drafted at a small scale and the thickness of the pencil line can become up to 1" wide when scaled! From those lofted lines, you will take dimensions to fabricate the parts of your boat.
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Ask questions on our support web site bateau2.com.
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