The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Lofting
Lofting as a discipline has taken a back seat to computer-generated plans and computer-controlled
machined templates and parts. Computers have taken over and are doing the time-consuming work of
describing and reconciling the three dimensional object (the boat) in two dimensions. A number of
computer lofting applications are available, and we can assume that price, accessibility, and features will
continue to improve.
But lofting and the knowledge of how to do it correctly have not diminished as useful skills to learn. <strong>The</strong>
fundamentals of descriptive geometry have broad-ranging application and infinite utility. If you know how
to loft, the computer cannot lie to you—you will be able to check its work. If you have never lofted, we
continue to urge new builders to loft a small boat (or even a large boat to scale) to understand the principles
and the process. <strong>The</strong> computer may break down, or the plans or the program may not have all the
detail you want for a specific project. Take the time to learn the skill of lofting, and it will serve you better
than any alternatives. For clarity, we use only English measures in examples of proportion and offsets.
Before you can actually build a boat, you must loft
its lines to full size. This means taking the small scale
plans of the design and projecting them to actual boat
size. Most boat hulls are complexes of curved surfaces.
Lofting guarantees that these curves flow smoothly into
one another with fair, even lines. Because lofting determines
the exact shape of the mold stations, success in
lofting means that the stringers and planking can be
easily applied to the molds and the resultant hull
will be fair and look and perform as the designer
envisioned. On the other hand, a poor job of lofting
will result in parts not fitting and a shape that is hard
to plank. Sometimes, poor lofting can lead to dissatisfaction
and abandonment of the project.
This process of drawing the lines that describe the shape
of the boat full size is necessary to correct the errors that
creep into the small-scale lines drawing that the designer
uses to develop the shape of the hull. For example, if
a boat were designed using a scale of 1" equals 1 foot,
for a 30' boat you would have a 30" lines drawing. You
would need to expand this 30" drawing 12 times in all
directions, and in doing so, you would also have all the
errors that were drawn into the lines drawing multiplied
by 12. This would result in inaccuracies that would
detract from the even, smooth curves of the hull.
Properly done, lofting corrects these inaccuracies.
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16
Making the corrections on the lofting floor rather than
after construction has begun saves a great deal of labor
and is necessary to produce a fair hull.
If you have never lofted a boat before, accurate lofting
will be time-consuming. In many ways, it allows you to
mentally build the boat before sawing any timber.
Thought and head scratching expended at this stage
will surely save frustration and errors after the actual
construction has begun.
Lofting is a process that is hard to visualize or understand
until you actually do it. To explain it abstractly is
difficult. Furthermore, each loftsman has his own tricks
for making the job easier, quicker, and more accurate.
We recommend that you look over this entire chapter
before you begin. If you are daunted by the idea of
starting out full-size, loft a simple boat on a large piece
of paper. This will help you get a feel for what you’re
doing.
<strong>The</strong> following is a general discussion of the procedures
involved. More detailed explanations can be found in
Boatbuilding by Howard I. Chapelle, Lofting by Allan
H. Vaitses, and Boatbuilding Manual, 4th Ed. by
Robert M. Steward. If you have access to a computer
and want to use it in the lofting process, consult
Steward’s book.