The Seamless Process of Hall Spars & Rigging
“For me, there’s only one way to do things – the
‘best’ way. Only the best people, the best tools, and the best materials
will give you the best results. And the best way is fluid – it’s always
evolving. Every day we’re pushing, testing,
and asking questions to ensure that our way is ‘the best.’ When you
walk through our factories, you can see and feel our commitment to
innovation everywhere you look. Whether it’s an engineer in the shop
discussing a new idea with the carbon fabricators or
one of the foremen evaluating a new tool, there’s a feeling of total
involvement. We’re all working to build the best spar that we can build .
. . the best spar anyone can build.”
-Eric Hall, president
The Best Way to Build a Carbon Mast
Experience is the most important tool in composite
construction. Experience translates into unmatched laminate quality as
well as continued process innovation. At Hall, we’ve worked with carbon
since 1984 and autoclave curing since 1992.
In fact, Hall is the only mast builder with more than two decades of
experience working with carbon.
Over the years, we’ve tested many
construction methods. Everything we’ve learned has led us to the
male-molding, autoclave-curing method. In combination with
the Hall molding technique, the autoclave produces seamless, virtually
void-free, tubes. Through testing (both our own and independent testing)
we’ve proven that the Hall process results in a spar that’s lighter,
stronger, and better. This is what led to the
initial investment in the autoclave in ’92 and to our acquisition of
the two long (40- and 46-meter) autoclaves in our factories today.
In Hall’s process, pre-preg unidirectional carbon
fiber is laid up around a shape-optimized mandrel (the male mold). The
carbon is applied one layer at a time according to precise engineering
specifications. Each layer of carbon is compacted
to remove any air bubbles. Then the complete piece is autoclave cured
to 6 bar pressure and a temperature of 121° C. The tube we create on a
mandrel is seamless and, due to aluminum mandrel expansion with heat,
the fibers are stretched straighter than with
any other method. Fiber straightness is basic to advanced composite
laminate performance: the straighter the fibers, the stronger and
stiffer the laminate. When the mandrel is removed, the tube is one piece
of uninterrupted solid carbon. No other manufacturer
uses this exact technique.
Mandrel molding, however, is not a simple process.
To eliminate the risk of wrinkling on the non-molded surface (in this
case, the outer surface of the mast) extreme care is required during the
carbon lay-up process. In Hall’s proprietary
process, each layer of carbon is carefully compacted before and during
the autoclave process to ensure wrinkle-free laminates even in
thick-walled tubes.
Mandrel-molded, seamless masts have tooled, smooth
inside surfaces. From an engineering standpoint, these surfaces provide
highly accurate and predictable areas for mounting close-tolerance
computer-machined fittings. And halyards slide
smoothly inside the mast.
Aerospace and Formula 1 builders use autoclave
curing because of its ability to produce aerodynamically superior
shapes. In combination with our proven strength characteristics, a Hall
carbon spar is the obvious choice for high-performance
applications.
The seamless mast is globally more aerodynamic than
masts made using other systems. The key element in rig/sail
aerodynamics is the mast’s ability to bend optimally for sail design
shape – at minimum weight. Without the baggage of lap joints,
glue, screws and filler that masts with full-length seams require, a
Hall seamless mast is lighter for equal bending stiffness. Yachts with
lighter masts heel less, maximizing sailplan aerodynamic efficiency. We
are not restricted by our tooling when it comes
to placing strengthening fibers in the laminate – fibers are applied
where needed.
Seamless masts have external reinforcements
(internal reinforcements would inhibit extraction of the mandrel and
inhibit proper fit of internal fittings). Wherever there is a tang,
spreader fitting, or hound box, there are external reinforcements
(doublers). Do they add drag? Computational Fluid Dynamic (CFD) studies
show that such doublers increase mast section drag (without sail) by
only hundredths of a percent. When the same section is attached to a
sail, the drag increase is virtually immeasurable.
Compared to the very measurable benefit of the lighter masts that have
them, these doublers are a non-issue.
Our shape predictions in pre-preg laminates are
extremely accurate; even with thick laminates, predictions are accurate
to tenths of a millimeter. The surfaces are so smooth that we’re able to
apply a clear-coat finish to the surface with
no weight-adding filler.
What you see through the remarkably accurate and
aerodynamically smooth finish of a clear-coat mast tube is the
fascinating array of the structural fibers themselves. In addition,
seamless masts have an unbelievably good track record. The
combination of autoclave curing at 6 bar pressure and profile
homogeneity creates extremely tough mast tubes. We invite you to visit
either of our factories and see our process. We guarantee that you’ll
agree – for tubular structures, nothing beats Hall seamless.
Benefits of the Hall Seamless Carbon Tube
• Weight: The Hall construction method eliminates
the need for any glue, screws, or filler. Therefore, Hall’s engineers
can accurately predict the weight of each mast before it’s built.
• Strength: Our obsession with compacting each
layer of carbon means the tube is virtually void-free. Mandrel molding
ensures that the fibers are perfectly straight—straight fibers are
essential to carbon strength.
• Stiffness: Again, because the piece is homogenous
we can accurately predict (and create!) optimum stiffness
characteristics throughout the spar.
• Aesthetics: Hall’s careful process results in a
tube so smooth (even though the exterior is not the molded surface) we
can beautifully clear-coat our spars. We use woven fabric as accent
material, giving the spars a beautiful finish.
• Aerodynamics: Each mandrel is shape optimized by
Hall engineers, using advanced FEA and solid modeling tools. The
laminate matches this shape exactly, and the resulting tube is perfectly
smooth and presents the optimum aerodynamic shape.
• Added bonus: The inside of the tube is perfectly smooth. Halyards run freely inside the mast, with nothing to catch or snag.
