The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

180 First Production Steps
case you may have to move the batten slightly in order
to make the section fair. If there is a major error, go
back and check through the development process. When
everything is right, this transom or angled bulkhead will
look similar to the vertical stations on either side,
although it will be expanded or more drawn out.
Curved Transom Development
It is quite common with bigger boats to have a transom
that is both curved and raked, either forward or aft, at
an appreciable angle. To develop transoms of this shape
is a little complicated, but the following instructions
and Figure 16-11 provide a fairly standard method.
<strong>The</strong> basic principles involved in the development of the
curved raked transom are most easily understood if you
consider the transom as being part of a cylinder. As with
the cylinder, it is curved in one direction (athwartship)
and straight in the other (fore and aft or vertical).
Looking at the lines plan, you will see that the buttock
planes intersect the transom as straight lines, these
being elements of the cylinder. You will use these
buttocks as you expand or roll out the transom from its
curved shape to a flat one.
<strong>The</strong> first thing to do is to project an auxiliary view of
the after sections of the boat and deck line at a line of
sight parallel to the centerline of the transom in profile.
(See Figure 16-11.) Begin by extending the centerline of
the transom in profile up clear of the other views. As
close to the other drawing as possible, draw in an auxiliary
grid centerline at right angles to this extended line.
Tangent to this intersection, swing an arc of the radius
noted on the designer’s plans for the transom. This is
the curve to which the transom will be laminated when
it is built. Measuring out from the auxiliary centerline,
draw in the buttocks parallel to this centerline, spaced
as they are in the half breadth plan (a, b, c, d). <strong>The</strong>n
project the points where the auxiliary buttocks intersect
the design arc of the transom down from this auxiliary
view to the corresponding buttocks in the profile view.
It is also necessary to determine the true intersection
of the sheer and the transom in this auxiliary view. To
do this, first project the intersections of the aft two (or
three) station lines with the profile sheer up into the
view. <strong>The</strong>se projections will intersect the auxiliary
centerline at 90°. Pick up from the half breadth plan
the distance from the centerline to the deck line or the
aft sections. Transfer these dimensions to the auxiliary
view, from the centerline out along the station projections.
Fair a batten through these marks. This sheer
line will intersect the arc of the transom.
Next, prepare the grid for the expanded transom. You
can use the transom centerline in the profile view as
the centerline for the grid or draw a centerline parallel
to it but a little away to keep things clear. Lay a batten
around the arc in the auxiliary view and pick up the
buttock spacing (a�, b�, c�, d�) and the point where
the arc intersects the deck line. <strong>The</strong>n transfer these
distances, laying the batten straight and at right angles
to the expanded transom centerline. Draw in the
buttocks parallel to the centerline and also lightly draw
the line (parallel to the buttocks) that represents the
intersection of the deck line and the transom (e�). This
gives one half the true width of the transom if it were
laid flat. Go back and identify the points in the profile
view where the projections of the buttocks from the
auxiliary view intersect the buttocks. Project these
points (m, n, o, p) out to the expanded transom grid,
where their intersections with their respective buttocks
will outline the shape of the transom.
If more points are needed for accuracy in developing
the shape of the outside edge of the transom, add more
buttocks to the body plan in between the standard
buttocks. Using a pick-up stick, transfer the heights for
the last three stations to the profile view. <strong>The</strong>n follow
the process used with the primary buttocks to get the
additional points.
It will be necessary to know the amount of deck crown,
so this, too, should be projected. Some designers give
the amount of deck crown as a percentage of beam at
any point, while others give a centerline that runs above
the sheer line to show the amount of deck crown. We
generally allow slightly more material on the transom
than is necessary for the deck camber by lightly drawing
a line parallel to the sheer, but above it, at least as high
as the deck camber will be at the stern. Draw this line
far enough to intersect the projected profile centerline
of the raked transom. From this point of intersection,
draw another line to the intersection of the deck line
in the outer corner of the transom. Give this line more