IBEX
with improved performance over exceeded, it continues to absorb energy ‘pass-through’ holes to allow the resin
Nomex in terms of strength-to-weight, through further deformation at a level to migrate from the inner skin, down
stiffness and fatigue. equivalent to around 50 per cent of the the cell walls to the outer skin. Infusion
The very latest development is original figure. grade is also suitable for RTM Lite.
polycarbonate honeycomb in which the
cells are tubular rather than hexagonal. 7<B3@</:AB@C1BC@3A 6=<3G1=;0>/<3:A
This gives the material a 3D rather Apart from being much lighter than Finally, there is PP with reinforced
than 2D structure, making its resistance ply, honeycomb absorbs vibration PP facings. This is more a panel
to stress in various directions more better by about 150 per cent. It is also than a pure core and is non flexible.
uniform. a great sound absorber. By varying the Honeycomb panels are used throughout
In Europe, Plascore is the only cell size, density, thickness and the industry for a multitude of purposes
company offering a full range of core characteristics of the surface scrim, it — particularly interior partitions and
materials, while other manufacturers can be tuned to a specific frequency doors — but boatbuilders seem to
tend to specialize in only one or two range. And because of the high have been relatively slow to adopt it
types. The marine industry is regarded percentage of sealed air space it is also for internal components, perhaps due
as offering strong potential growth for an efficient thermal insulator. to reservations about longevity in the
honeycomb because manufacturers Although boat cores are rarely marine environment.
are convinced it offers numerous exposed to tensile strength challenges, These lightweight, structural
advantages over foam — and is now honeycomb performs very well in composite sandwich panels are
coming down in price. this respect as the ‘hat’ section at the designed to add strength to primary
When it comes to boat construction, interface between cell and scrim (which and secondary structures while saving
issues other than pure bending have Plascore refer to as the veil) produces time on the shopfloor.
to be taken into consideration. The an excellent geometric lock. For most boatbuilders, strength
impact resistance of the outer skin is Plascore’s PP Honeycomb comes in of secondary structures — such as
crucial, and extra thickness here might four basic varieties. The first is a true furniture carcasses and galley units —
allow the specification of the core or, open cell structure with no veil. Its isn’t a big issue, but weight reduction is
in certain circumstances the inner main use is in thermoplastic moulding assuming ever greater importance.
skin, to be reduced. Boatbuilders can of sandwich structures. PP Honeycomb is available with a
decide whether to take these benefits The second consists of the core with 1.5mm Okume ply facing ready for
to achieve reduced thickness with the either a plain non-woven polyester veneering — or finishing with any other
same stiffness, or stick with the same veil or the same veil with an inner film suitable material such as leather.
dimensions and up the stiffness. barrier layer. Standard honeycomb panels do not
have the veneer quality demanded
by the recreational boatbuilding “The latest material is polycarbonate
industry, but separate veneering by a
honeycomb. The cells are tubular rather specialist company gives the builder the opportunity to ensure that the final
than hexagonal giving a 3D structure” appearance is exactly as they wish.
1=<1:CA7=<
Coring of decks, superstructure The veil is scored with a grid pattern Core material technology continues to
and topsides is now the norm in to aid draping. This material is ideally develop in different ways, with impetus
recreational boatbuilding but the suited to GRP layup, either in a purely added by the increasing acceptance
question of using cores below the open mould or with vacuum bagging. of resin infusion and other closed
waterline is still a matter for serious As with other faced core materials, mould processes. Boatbuilders are now
debate. double curvature is dealt with by looking beyond the intrinsic advantages
Here, an additional advantage of cutting the inner veil and if necessary of stiffness and reduced weight to
honeycomb is that each cell is sealed removing sections until a snug fit acoustic and thermal insulation,
top and bottom by the bonding of the is achieved against the mould tool and long term resistance to water
outer and inner skins. In the event surface. infiltration. It is honeycomb’s good
of a puncture, water cannot migrate Infusion grade PP Honeycomb is performance in a number of such areas
into other cells around the damaged exactly what its name suggests. In this that is making it an increasingly viable
area. The mechanical properties of the case the veil normally has pre-punched proposition.
material aren’t affected by moisture,
so there will be no further decay of
the core even if repairs can’t be done Material properties
immediately.
If there is debonding of the outer Flexural response Shear strength
skin around the immediate impact area
(allowing water into adjacent cells) a Balsa
moisture meter will quickly reveal its Compression SkinFoam
extent. Honeycomb
Honeycomb also performs better Core
following failure than either end-grain Shear
balsa or foam. Rather than breaking Sheer stress Skin
down suddenly if the sheer stress limits
are exceeded, it tends to progressively
distort, retaining some performance 0 10 20 30 40 50 Tension
even in a damaged condition. If Shear strain %
its compressive yield strength is
www.europeanboatbuilder.net s August/September "!
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