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What is it? Polypropylene honeycomb…
think of a huge bundle of polypropylene tubes bundled and welded
together. Now cut off a slice from the end so you have a sheet
about 15mm thick with the ends of the tubes facing out. Lay on
a light skin to keep resins from flowing in and filling the tubes
and that's how
it normally comes to you. (I understand the supplier can furnish
pre-glassed panels on order, even full length) Then you cut to
shape and apply fibreglass in conventional style. Since most
of the panel is air, it's lightweight and apparently it's quite
stiff though the balsa is stiffer yet. Ian says a 15mm Polycore
panel should be used to equal or slightly exceed the stiffness
or sheer strength of a 12 mm balsa panel. According to Ian's
estimates, the cost saving is significant!
Since Ian did his own design work, he sent
his cad drawings to a local CNC mill operator. These
computerised mills can cut, with precision, any number of
panels from a nested pattern so that full length sections can
be assembled from the various pieces cut out of
4 X 8 foot (1200X2400) sheets. This can be done with balsa, ply
or whatever.
Ian didn't want his panels cut out but
it would save an immense amount of time and increase accuracy
to have them marked for shape. So he designed a gadget for the
mill that just held a marker in place instead of the cutting
tool. For a few hundred dollars all the panels were clearly marked
so they could be cut later with a knife. Brilliant! Lofting all
those panels could take weeks and human accuracy could not equal
the machine.
At the shed rented from Maryborough Slipway,
the pieces are made into subsections. There is a table top made
to length covered in common black builders plastic. The kind
you lay under concrete work. Great stuff. Cheap as chips and
even epoxy won't stick to it. There Ian assembles the pieces
for full length panels. He prefers to cut a sloppy line just
outside the marks. Ian claims this is an advantage as the raw
edge of the glass can be a dangerously sharp surface after setting
and hanging over the panel sheet but with a little extra sheet
the glass doesn't have to extend past the edge. The marked line
is still quite visible through the glass later so trimming to
exact size isn't a problem as long as the trimming is done with
the resin still green and soft.
They lay out the pieces and hold down the
butt joints with bits of light timber screwed into that excess
panel edge and the table top. This stabilises the layout and
prevents warpage as Ian notes the vinylester resin he uses seems
to expand slightly in curing. Ian says the panels are sometimes
not square so the butt joints can be a little uneven. A Bosch
hot glue gun is what Ian uses to fasten the joints. He prefers
that tool because of its unique tip shape which allows you to
press past the skin to insert the glue in the right spot. As
the empty sections of panel can absorb a lot of glue, you don't
need to try to fill it up. A calloused finger tip to clean off
the excess (oohh hot hot!!) and a little bogg to fill leaves
the joints ready to go.
Next comes the fibreglass. 750 gram tri
ax was recommended but Ian feels a 750 DB may be a little better.
Whatever, the material is cut to shape and size and rolled up.
Starting at one end, the resin is applied to the panel with a
paint roller. Then the cloth is laid down and resin applied to
it followed by peel ply. This is all done in sections as the
resin has a pot life of only about 20 minutes.
Proceed as above until completed with that
side. Ian says that for panels that require a little twist in
them to mount, he takes the panel that has been glassed on the
one side (inside) and mounts on the project before application
of the glass on the outward side. Or.. check it briefly, then
back on the table, glass the outside and trim and mount as soon
as possible as the green fibreglass
will have malleability that it won't have later.
For the chamfer, bilge, shear panels etc.. Ian saved the outside
layer of glass for last and doing the whole section at a time.
Preferring to work underneath but saving a lot of taping and
more difficult fitting.
This is all very similar to the process
that I was advised to use with foam when I was talking to notable
builder/designer, Bob Burgess a few years ago before I was persuaded
to go with the balsa core stuff. With some variation this general
process would work for any flat panel material. Foam, ply, balsa
or Polycore or… the innovation is the use of the CNC mill
as a marker.
Taping the panels together inside is conventional.
Ian's fitout is complex and he uses it for structural stiffness
so there is a
lot of small sections to do but, his modular construction method
helps as the work is sooo accessible. Whenever possible a section
of the boat is built on the floor or table and then joined to
the rest of the boat as required. Each section is built so that
no more than 4 people are needed to manhandle it into place.
This modular technique served him well in the construction of
Vega and you won't find him abandoning what works! In these photos
note that the cockpit assembly is yet to be mounted.
Ian has some legendary helpers working
with him so the project is scheduled to go very fast. I won't
jinx it by saying how fast but.. we should have time to keep
an eye on this for the next couple editions to see how they go.
I know I'm learning valuable information..
maybe you are too….
Below is a photo report. |
