Lofting

Lofting is a carpentry technique (sometimes using mathematical tables) whereby curved lines are drawn on wood and the wood then cut for advanced woodworking. The technique can be as simple as bending a flexible object (such as a long cane) so that it passes over three non-linear points and scribing the resultant curved line, or plotting the line using computers or mathematical tables.

Lofting is particularly useful in boat building, when it is used to draw and cut pieces for hulls and keels, which are usually curved, often in three dimensions.

Basic Lofting

Lofting is the transfer of a Lines Plan to a Full Sized Plan. This helps to assure that the boat will be accurate in its layout and pleasing in appearance. There are many methods to loft a set of plans.

Generally, Boat Building books have a detailed description of the lofting process which should help you far beyond the scope of this article. My preference is to loft my plans on a level wooden floor, marking heavy paper such as Red Rosin for the full sized plans or directly on the plywood sheets.

The first step is to lay out the grid, mark the Base Line along the length of the paper or plywood sheet. Then nail Battens every 12 inches (or more in some cases) where the station lines are to be set as a mark for the perpendicular line, which is marked with a T-square. The previous steps are followed in turn by marking the Top Line and the Water Line. Before continuing make sure to check the lines by using the Pythagoras' theorem and make sure the grid is square.

The second step is to mark the points from the table of offsets. All measurements off the table of offsets are listed in Millimeters (which I prefer) or the standard Feet, Inches and Eighths. The points are plotted at each station then use a small nail and a batten to Fair (draw with a fair curve) the boats lines.

Definitions

Full Sized Plan a 1:1 scale construction drawing of a boat and its parts Lines Plan a scaled down version of a full sized drawing often including the body, plan, profile and section views
Body Plan is a view of the boat from both dead ahead and dead astern split in half
Plan view is looking down on the boat from the top
Profile View is a view of the boat from the side
Section View Cross section of the boats width

Batten long stick to help draw fair lines