Speaking of the difference, I've often wondered if they use different
resins in vacuum molds. In the roller method, the epoxies are fairly
stiff (usually due to the "induction" time in which the catalyst acts
on the resin), but it would seem to me to achieve proper penetration
of the glass in a vacuum system, the liquids would be fairly light.

Yes/No?


***************

I was invited to the 25th Anniversary celebration of a local
manufacturer, Nordic Tug.
They had a few hundred people in attendance, from all across the
country, and almost all were Nordic Tug owners. Impressive turnout
during one of our rare snowy days and in the middle of January, but it
was like the gathering of an enthusiastic clan. I digress....

Nordic had a number of vessels on display in all stages of build and
fitout. Nordic had set up a demonstration of vacuum bag, or infusion
molding, in the laminate shop. We observed the molding of a cabin top.

The gelcoated mold gets one layer of vinylester resin prior to the
layup. This is to prevent "shrinkage" which could spoil the exterior
appearance of the finished component.
The glass mat and coring materials are then laid in place. For the
cabintop, Nordic uses three different weights of mat in the layup and I
would need to dig out my notes to be specific as to how many ounces
each fabric is rated. Many of the superstructural components in a
Nordic are cored, and a combination of serrated balsa as well as
synthetic coring materials are used in the buildup. All coring material
is designed to allow resin to flow throughout the layer, vastly
reducing any liklihood of a future separation between the FRP and the
core.

There is a difference in the layup process when preparing for infusion
molding. There are certain materials included that promote the flow of
resin throughout the layup and the entire process is conducted with an
emphasis upon assuring a maximum, thorough wet out. It isn't just the
same layup one would use with roller laminating and then vaccum
infused.

Once the layup is completed, a plastic sheet (vacuum bag) is placed
over the mold and some plastic tubed "plumbing" installed to remove the
air from the bag and create a vacuum. When the vaccum has been
estabished, the technician uses an electronic sensing device to check
the perimeter and the central vacuum connections for any leaks. After
the integrity of the vaccum is assured, the infusion begins.

Nordic uses vinylester resin. The technician explained to us that a
number of factors are considered when adding the catalyst to the resin,
including ambient temperature, of course.
The resin itself was heated to a controlled temperature, (about
70-degrees), and then the catalyst was added. It would be hard for me
to compare the density of the infusion method resin with what the
density might have been in a roller lamination- but I have no doubt
that the mixture was calculated to be optimal for infusion molding. A
valve was opened to allow the mixture to flow into the mold, and during
the minutes required for the dark colored resin to spread throughout
the mold the technician was constantly monitoring the flow and spread
of the liquid.
The greater atmospheric pressure outside the bag helped press and
squeeze the resin into the mat.

Nordic has been infusion molding cabin parts for some time now, and has
become so confident in the process that beginning in March or April
they will begin vacuum bagging their hulls as well.
When you put a ten year hull warranty on a million dollar boat (some of
the larger models are now well over the 7-figure mark), you want to be
sure the technology is first rate.

There are some potential advantages, in my opinion. For instance, the
assurance of a "wet" layup. I suspect that in many of the traditional
"hand laminate" processes there are gaps at lunch times, shift changes,
etc where an underlying layer of glass is allowed to cure just a bit
more than desirable before the next layer is applied....possible source
for future delam.
There is less opportunity for dirt, dust, etc to find its way into the
laminate and that can additionally help reduce the liklihood of
eventual blistering. The use of chopped strand to build up thickness is
inconsistent with vacuum bag molding.

Opinons from OZ not withstanding, there is no reason to assume that
infusion molding will always be done poorly and traditional roller
laminating always done well. I'd be happy with a well built boat
constructed through either process.