|From a Bare
Deck Frame Layout
Without a detailed set of construction designs and drawings, each step
in the construction process required a substantial amount of visual layout
and what amounted to full-scale lofting of the basic shapes of the deck
crown and cabin trunk. One of the reasons I chose to make the midships
bulkhead so oversize was because it would make an excellent platform
on which to produce full-scale lofted drawings of the deck, where I could
properly visualize the shapes before committing to anything permanent.
single construction drawing showed a maximum deck crown of about 3"
at the theoretical highest point, which equates to just under 3/8"
per foot of maximum beam. With this figure in mind, I began my
"lofting" process by striking level lines on the mid bulkhead
from each sheerline, simply laying a long level on the edge of the hull
and drawing the appropriate line on the plywood. I was pleased
(though it shouldn't have been any other way) to note that the lines from
each side intersected nearly perfectly in the center, reinforcing the
levelness of the hull. I always find that it's handy to have these
small vindications from time to time during any construction process--a
valuable form of checks and balances. After determining the
centerline, I marked a perpendicular line on center, and marked the
3" height above the level base line.
Next, I consulted several sources to determine the appropriate way to lay
out a proper deck crown. There are a few schools of thought here,
each with their own proponents and naysayers. The first school says
that the crown can simply be a true arc of a circle, with points running
through the two edges and the maximum height at the centerline. The
general consensus seemed to be that this method was amateur in nature and
produced unpleasing crowns from a visual and practical nature, and is not
highly regarded. I never seriously considered it.
second, and most traditional, school offers a detailed method of beam
layout that produces a variable arc that flattens towards the top, yet
intersects with the edges at a smooth and pleasing angle. I found a
description of this method in Details of Classic Boat Construction,
by Larry Pardey, but it is widely available in other resources, such as
Chappelle. I reviewed the merits of this particular technique and
decided that it seemed to make sense for my application, and was also
fairly straightforward to understand--at least after an initial few
minutes of head scratching.
The final school argues that the
traditional method, in which all deck beams share a single shape and mold,
produces a deck that, when viewed from the theoretical side, may appear
inappropriately shaped as the beams progress from stem to stern. For
certain applications, such as a truly flush-decked boat, there is logic to
this argument. This method opines that each beam should be uniquely
shaped according to its position, to avoid the appearance of a hogged deck
amidships that might result when using beams built off a single
mold. A recent article in Wooden Boat magazine covers this
method in some details; I shan't repeat it here. I rejected this
particular method because there was so little actual deck in my design,
with most of the boat taken up by the large cockpit with narrower
sidedecks outboard, and I couldn't see the virtue in following this method
for very little actual return in my particular case. That said, the
method probably would bear further investigation in certain
circumstances. Each case is unique, and therefore must be addressed
individually as needed.
It took several reads of the section in
Pardey's book before I understood the whole process; some of my research
even included a trip through my old Geometry textbook to refresh my memory
on how to divide an arc. For more, click on the link below.
to read a detailed account of the beam crown layout method.
the shape drawn out full-size on the bulkhead, I found I could easily
visualize what the decks might look like, and decided that I was pleased
with the result. I decided to continue using that shape, so it was
an easy step to transfer the measurements to a length of 2x10 that I had
laying around, from which I cut a test beam and, ultimately, a laminating
mold upon which to glue up the many deck beams needed. More on the
beams' construction is coming up in subsequent pages. Jump
Cabin Trunk Crown
The other reason I left the mid bulkhead oversize is that it was destined
to become the demarcation point between the cockpit and the cabin
trunk. As such, it of course was the perfect place to draw out the
designed shape full-size, which was necessary not only to reinforce the
accuracy and visual effectiveness of the drawing, but also to provide a
cutline so that I could remove the unnecessary portions of the bulkhead
and cut it down to the proper shape.
here to refresh your memory on the design concept.
used the same method of crown layout as I did for the deck beams, though
in this case the maximum height was 6" above the cabin trunk
baseline--a substantial crown over the 4'+ width of the cabin trunk, but
this is a typical design feature of similar trunks, and was required in
order to create the proper visual look called for in the drawing and
concept. I also laid out the proper width of the trunk sides, the
sidedeck widths, and three versions of the cabin trunk sides:
vertical, outward 5° angle, and inward 5° angle.
to read a detailed account of the beam crown layout method.
the shape of the after end of the eventual cabin trunk correct was
critical before making any cuts in the bulkhead. Because the entire
deck design is wrapped up in the overall shape of the cockpit--and, by
nature, the cabin trunk, since the trunk is essentially intended to be a
seamless continuation of the cockpit coamings as they sweep around the
forward part of the boat--many of the following steps would hinge directly
on the bulkhead shape, so it needed to be right. With the basic
shape drawn on the bulkhead, I left it alone for several days, taking time
now and again to glance at it, absorb the shape, and see what I
thought. I saw no need to rush the cutting, but it was clear that
I'd need to make the cuts sooner rather than later.