I located 1" square fiberglass
pultrusion tubing, which is made from the same vinylester resin that we use
for bonding and laminating, and had 20' shipped from California. Several
tests were conducted to evaluate the bond-integrity and net strength of the
joints. The
pultrusion inserts' bonding surfaces were prepared by sanding and acetone
rinse to assure maximum adhesion with the resin and filler. This end-view
shows a cross section from the test joint.
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| Optimum results were achieved
by pre-wetting the inner surfaces of the panel's scrim (where the honeycomb
had been removed) with a "slow" activated coating of resin, then forcing
a VERY thick filler into every crevice of the remaining honeycomb along the
exposed scrim. The filler is a mixture of milled-fiber (1/32" long
fiberglass strands) and vinylester resin which is blended to a "thick oatmeal"
consistency. Last-minute adjustments to viscosity are accomplished
by adding small amounts of Cabosil before activation. The joint is
stuffed full of the "slow" activated filler then the pultrusions are inserted.
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Both panels are clamped (flat
/ square / parallel) on the builder's wing tables with their ends butted
to assure a minimum seam. Numerous clamps, straight edges and weights
are required to obtain the desired alignment in 3 planes.
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| The resulting Side Wall panels
are amazingly stiff, lightweight and have precise geometry for subsequent
installation of the sliding windows. |
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The main cabin's Aft Wall
also has seams within the cut-out for a sliding window, so the same joining
method was applied. This wall is HUGE (15' wide x 88" high) so several
seams are required to combine the panels. A modified version of the
joint was used at these seams; the polypropylene honeycomb's removal-depth
was adjusted to position the pultrusion precisely in the middle of the seams.
Similar results were realized.
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| The completed wall is lightweight,
stiff and has perfect net-shape features for installation of the door and
windows. |
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Side Walls butt against the
plumb Aft Wall to provide fore-and-aft stiffness for this wide load-bearing
span. The galley counters' end panel, adjacent to the 39" wide doorway,
is similarly butted against the aft wall for additional strength. All
intersections are laminated using multiple layers of bi-axial cloth with
both 0°-90° and 45° fiber orientation for superior strength.
A massive 16' long I-beam is clamped along the span during assembly to assure
flatness.
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The forward ends of the Side
Walls attach to the main 2" bulkhead which spans the vessel at the
mast tube's centerline. This bulkhead
is the most highly-stressed,
so fit and alignment of the panels is critical. After careful measurement
of all as-installed geometry, I tweaked the computer model to reflect assembly
variances and cut each side on the ShopBot. Final dimensions were within
±.125" of the designed gap! Notice the jack under the mast tube
... the bridge deck floor was raised slightly
to achieve a positive .188" bow before the main bulkhead panels were placed.
After all main bulkhead laminations are completed and the jack is removed,
compressive loads will be much higher at the top as the hulls regain their
normal alignment while the bridgedeck floor assumes longitudinal tension
loads. I-beams are also clamped along the bulkheads to assure flatness.
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This view shows the first
lamination around the mast tube. The forward sides of the main bulkhead
panels are also bonded in this manner before laminations to the 2.625" forward
wall and aft brace commence. Notice how the sunlight illuminates the
upper portion of the mast tube? After laminations to the pilothouse
roof and windshield panels are completed, this area will be much thicker.
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The intricate laminate schedule
is often difficult to visualize but this in-progress picture helps.
The first athwartship laminate to the mast tube, pictured above, can now
be seen through the long vertical laminates on either side of the mast tube.
Darker areas indicate more layers of resin-soaked bi-axial fiberglass material.
The horizontal laminates on the right tie the upper 2.625" members to the
lower 1.5" panels. Notice the multiple layers at the floor.
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Seen from the forward side
(in the master stateroom) the transition from 2.625" thick upper members
to the lower 1.5" panels is apparent. Look closely at the mast
tube ... the darker area just below the main bulkhead seam is a full laminate
that connects the settee arm (aka mast brace) with the 2.625" thick wall
which separates the two staterooms. This ties the two, along the vessel's
centerline, with the mast tube for additional stiffness. Long vertical
laminates then tie the stateroom wall with the mast tube, similar to the
aft side, and overlap previous layers. The vertical laminate layers
on the left connect the main bulkhead to the hull and the floor. They
wrap around the corner and extend forward all the way to the bed cut-out.
This bulkhead is solid! A short section at the floor remains to be connected,
then this portion will be complete.
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Here the main bulkhead is
almost completed. Pre-cut fiberglass pieces are awaiting installation
at the port side of the guest stateroom. One of the massive exterior
bedroom walls is visible on the left, over the master stateroom doorway.
These 2.625" thick wedge-shaped panels tie the bedroom roof to the side decks
and connect both bulkheads for additional strength.
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