| All three roof
panels
were designed with common geometry to enable re-use of a single mold
for
fabrication. The raised pilothouse and galley roofs are 16' wide
while
the trapezoidal cabin top, over the beds, tapers from 15' to
12.5'
wide. |
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The Pro/DESKTOP 3D computer model data was used to design
the
12 identical ribs for the mold. Each rib has precision slots for
(9)
1x4 slats and (3) 2x4 lower braces. The ribs were cut from (2) 4'
x
8' sheets of hardwood plywood using the ShopBot CNC router.
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Assembly only required a small hammer to nudge the spruce
boards
into their respective slots. Deck screws were used to retain the
boards
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Two layers of 6mm luan mahogany plywood were then applied,
with
seams staggered, to provide a stable base for the white Formica mold
surface.
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Edge features of the pilothouse roof are created along the
periphery.
Patterns for the compound forward edge, aft corner radii and mast-slot
were
cut on the ShopBot to simplify fabrication. An edge radius and
draft
angle were added manually using two-part filler (green in the picture).
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| After careful preparation and
multiple
applications of mold-release agents, lay-up commenced. White
gel-coat
was followed by layers of resin and tri-axial fiberglass cloth. A
polypropylene
honeycomb core was laminated next, followed by more layers of resin and
fiberglass.
1" thick Nida-Core panels were finally added for the center
reinforcement
beam and cornices. A spotlight, winch and other accessories will
be
mounted through the center panel while the cornices will hide interior
lighting
and provide mounting edges for the pilothouse headliner. The
assembly
was allowed to cure in the mold over the weekend for strength before
removal. |
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The splotchy green patina on the
finished
pilothouse roof is just PVA mold-release; it washes off with
water.
Since all features were incorporated into the mold's design, negligible
finishing
work is required. Surface finish of the gel coat is adequate to
use
as-is, since most areas will be obscured by the solar panel
array.
Notice that the mold is being prepared for the next roof panel.
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The saloon roof (over the galley
and
bar) design shares most features of the larger pilothouse roof.
The
forward end of the mold was simply masked-off as needed. Spray
application
of the gel coat finish followed immediately. Click the image to see a short video
clip of
the process.
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| This roof panel is less-stressed
than
the enormous pilothouse roof, so one layer of fiberglass cloth was
deleted
from the lamination schedule. This was also our first application
of
bi-axial roving in lieu of the tri-axial cloth used for the previous
panel.
Weight savings is considerable. In this picture, all but the
center-section
of the second layer have been applied. Notice the staggered seams
of
the fabric in these layers ... this results in a smoother surface
transition
with reduced stresses. The "ears" visible at the forward edge
will
index into pre-cut slots in the pilothouse walls. Click the
image
to see a short video clip of the lamination process. |
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Valences were added,
corresponding
to those on the pilothouse roof, then laminated in-place. These
end
just 1/2" away from the aft wall to facilitate installation. The
remaining
roof will form a 14" eave over the wall's sliding door and windows for
rain
protection. Re-use of the mold's 6" corner radius features
results
in a strong net-shape part which requires negligible finishing.
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This view, looking aft along the
starboard
edge, shows the ear, valence and corner features. Curing
time of this panel was quicker due to the reduced number of
laminates.
The resulting part is lightweight, strong and ready-to-use.
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The slanted (5°) deck over
the
beds is trapezoidal in shape and narrower than the two roof panels, so
the
mold was masked-off to the desired shape. An integral rain gutter
is
incorporated into the forward edge by installing a half-round insert to
the
mold. This will divert water away from the eave overhanging the
bedrooms'
forward portholes. Here, as the first layer of fiberglass is
about
to be installed, the insert is visibly protruding from the gel coated
mold
surface.
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The finished roof is left to
cure
in the mold. The darkest area is the rain gutter feature.
Surface
finish of the net-shape part was, again, excellent. This mold has
saved
considerable time and expense while resulting in beautiful components.
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