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| From a Bare Hull: Cabin Trunk (Page 7) |
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Cabin Trunk Deck Beams
Much earlier, I had transferred the shape of the overhead curvature, as defined by the shape of the midships bulkhead (at the aft end of the cabin), to a scrap of pine for future reference. Now, I used a jigsaw to cut out the shape as a template, for marking purposes only. |
 With 6 beams to fabricate, I hoped to build several duplicate laminating molds
so that I could speed up the process and laminate several per day. To
build the simple molds, I began with a sheet of plywood, which I covered with
plastic for protection. Then, I marked the shape of the beam template
directly on the plastic in four locations. Since the curvature required
was not extreme, I built the molds of small blocks of scrap 2x4 that I screwed
to the plywood in 7 locations for each mold. This became tiresome, and
after building two molds I decided that finishing the beams in three laminating
days would be just fine, so I called it quits and moved on to other related
tasks. |
 Next, I had to mill the various strips that would form the curved beams.
From some mahogany stock, I milled a total of 18 strips, each a little over 1"
wide and about 3/8" in thickness, and close to 8' in length. I only needed
a maximum of 7 feet for the widest beam, but for the moment kept all the strips
uniform. The 18 strips, at three strips per beam, was enough for the 6 total
beams required. The milling process took the remainder of the afternoon. |
 Over
a period of three days, I laminated the six total beams required to span the
coachroof opening, two per day. I glued each beam from three strips
of mahogany set in thickened epoxy resin adhesive, and clamped them tightly to
my forms for 24 hours till they cured. At the end of the period, I had six
messy beams ready for final milling. |
 Since
the beams were laminated with one side pressed against smooth plastic, that side
was relatively flat and smooth, and was suitable for running against the planer
table. Therefore, I could use the planer to remove the bulbous epoxy
spillout on the top edge, and acheive a uniform thickness. Over a number
of passes, I cleaned up all six beams till both sides were smooth, and the beams
were consistently about 1-1/4" in width. Now they were ready for final
fitting and installation. |
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 First,
however, I needed to work on some layout. Since I had planned a
keel-stepped mast, my first order of business was to locate a beam on each side
of the mast step, to begin the reinforced area around the future mast partners.
To locate the first (after) of these beams, I laid a strip of plywood (one that
I use in the shop as a straightedge) across the cabin trunk and aligned it so
that it was parallel with the midships bullhead. With a plumb bob, I
located the after edge of my built-up mast step in the bilge, and aligned the
plywood so that the bob was just a bit aft of the step. |
 After
double-checking the measurements from the bulkhead, I marked the cabin trunk on
each side, representing the forward edge of the beam. Then, I made a
second set of marks to locate a beam on the forward side of the step area.
The distance between these beams turned out to be just over 9", and was close
enough to the forward edge of the cabin trunk that no more beams were required
there. |
 With
the first two beams located, I laid out the remaining four beams. By pure
dumb luck, the space remaining between the midships bulkhead at the aft end of
the cabin and the beam aft of the mast partners turned out to be such that the
spacing between the remaining beams, keeping them evenly spaced, ended up within
a sixteenth of an inch of the preexisting spacing already determined by the two
mast partner beams, so all six beams ended up evenly spaced. This was a
pleasant surprise. |
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With the remaining four beams located, I moved on to trimming and installation. Each beam required angled cuts at the ends to allow them to fit into similarly angled notches that I would cut in the cabin trunk walls. With each beam (one at a time) set on top of the cabin trunk in the proper position, and using marking and cutting techniques more or less identical to those used when I installed the short sidedeck beams earlier in the building process, I first marked the end of the beam at a point about halfway through the thickness of the cabin trunk, or about 1/2". I had previously marked the fore and aft edges of the beams on the trunk, during initial layout. Then, I marked the bottom edge of the deck beam at its intersection with the cabin trunk, which would equate with the bottom of the angled notch once the beam was pushed downward into position. |
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 Other
marks required on each beam included the top edge, which was in line with the
mark on the cabin trunk for the depth of the notch, and plumb marks on the
inside of the cabin trunk itself, as well as a final horizontal line at the
depth of the beam, which signified the final edge of the notches that would be
cut into the trunk.(Note: this is a challenging process to describe. It would be easy to show you, but it's hard to put clearly into words. Please forgive me.) |
 With
the various marks made, I cut the ends with a small backsaw, and then cut out
the angled notches in the cabin trunk with the same saw, holding cutting
carefully along each edge of the marked opening and angling back to the mark
halfway through the thickness of the trunk. Then, I made several
additional cuts in the center to make chiseling out the waste easier, which was
the next and final step. |
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 The
first beam required several minor adjustments (shortening) before it fit snugly
into place, since it was entering into a highly curved section of the cabin
trunk. The remaining beams' fitting went quite a bit quicker, but the
entire process was still rather drawn out and labor intensive, and took up the
bulk of the day. Note that the final beam, not seen in these photos, would
end up directly against the bulkhead. |
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 In
the end, though, the beams clearly and pleasingly defined the shape of things to
come for the coachroof. It was clear that some beam fairing would be
required, particularly at the forward end, to ensure that the coachroof
maintained the proper curvature had angle forward, but this was to be expected.
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 Down on the bench, I routed the detail on all 6 beams, and sanded each with 120
and 220 sandpaper until they were smooth and ready for finishing. Then, I
installed the beams permanently with thickened epoxy resin (using mahogany wood
dust for color), and a single bronze screw in each end, driven in from the top
of the beam where it wouldn't be seen. |
 Once the beams were installed, I pretty much left the boat alone for the rest of
the day, as I didn't want to accidentally strike or run into one of the beams
while the epoxy was still curing; the beams were so low that it was very easy,
and common, to accidentally run into them. |
 When the epoxy cured, I sanded the joints and began the varnish process on the
beams, which I wanted to complete before installing the overhead permanently.
Over several days, I built up a number of base coats of gloss varnish on the
beams and inside of the cabin trunk, which really started to bring out the
character of the wood.Next: Installing the coachroof. Please click here to continue.> |
