The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 16 – Lofting 173
intersections of the waterlines and the centerline, and
somewhere out in the body plan crossing an intersection
of lines, possibly that of a waterline and buttock. If
this is not the case, you will have to use whatever other
information the designer supplies to develop the diagonals.
This may be an angle measured in degrees. Once
you have located these diagonal lines on your body
plan and have double checked them, ink them in. Use
a different ink color from that used for the other lines
and be sure the color you pick will be easily distinguished
from the color you are using for the waterlines.
Later on, waterlines and diagonals will be coming close
together at low angles in the half breadth view of the
lofting, and you need to take care not to get them
confused. <strong>The</strong> grid is now completed.
<strong>The</strong> Sheer Line
Although some expert loftsmen lay down several lines
at one time, we find it less confusing to lay down and
fair one line at a time, making sure it is correct before
going on to another.
<strong>The</strong> first curved lines we put down in lofting a hull are
the lines which outline the profile of a boat. Usually we
begin with the sheer line. Go to the table of offsets for
the profile view, given in distances from the baseline.
<strong>The</strong>n, at each station line, carefully measure the dimensions
from the baseline given in the offsets. Lay a fairing
batten on these points.
To fair a line: Select or mill a batten that will bend into
a curve between the points to be faired. <strong>The</strong> object is to
get the right flex—not so stiff that the batten breaks or
moves the weights, nor so flimsy that the batten waves
and makes it difficult to lay down a fair curve. First, lay
the batten so that its edge is on the marks where the
sheer line meets the foremost and aftermost stations,
allowing equal overhang at each end. Hold it there
using either lofting weights or small nails. If you use
nails, put them beside the batten so the batten can slide
lineally when you make any corrections (i.e., never nail
the batten to the lofting). Go to the mid-station and
push the batten until its outside edge is on the mark
and secure it in position. Continue moving the batten
at the station marks, making the batten touch every
point if possible.
If there seem to be any errors at this point, i.e., the
batten is 1 ⁄2" (12mm) or more off a mark, we first
check to see if we have made any errors in taking the
measurements from the offsets. If not, we then check
the lines drawing with a scale rule to see if the offsets
are correct. If it appears the designer has made a major
error in transferring the measurement from the lines
drawing to the offsets, we measure the lines drawing as
carefully as possible and transfer the new measurement
to the profile view. We also correct this in the table of
offsets.
Once we have checked for major errors, we move
the battens off the measurement points the minimum
amounts to attain a fair curve. <strong>The</strong>re is no scientific
formula for the fairness: the curve should be pleasing
to the eye, and it should have no humps or flat spots.
<strong>The</strong> best way to check a curve is to get your eye down
level with the batten and sight along it looking for
deviations.
Take your time sighting the batten to correct any errors
in the curve. Move the batten the least amount possible
to establish a fair curve and sight along the batten again.
Once you are satisfied, draw the sheer line in ink. <strong>The</strong>
color used in drawing the buttock lines in the grid would
be good for the sheer line and other profile lines.
Other Profile Lines
<strong>The</strong> other lines which outline the profile of the boat are
the keel line and the lines for the stem. Lay these out
in the same manner as you did the sheer line, taking
the measurements from the table of offsets and using a
batten to fair the lines. Ink the lines when they are fair.
In boats that have planking that ends in deadwood,
there will be a rabbet line. This usually shows the
shapes of the inner keel and stem and should be laid
out too. We don’t have a rabbet for the planking in
our method of construction because we laminate the
deadwood and outer stem on the hull after planking.
<strong>The</strong> Deck Line
<strong>The</strong> next line we lay out is a half breadth, or top view,
of the deck line. <strong>The</strong> offsets for this line appear in the
table of offsets shown in half breadth from the centerline.
Transfer the measurements and fair this line as you