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wrote:
K. Smith wrote:

wrote:

30. JIMinFL

I think you could strip all the gelcoat entirely off a boat and it
would still float. If the fibers were adequately wetted out with resin,
the hull wouldn't even absorb water (or "wick" it around). That seems
to be where we disagree.

Now you are qualifing with "adequately wetted out with resin". Sure
some
better hulls will be more resistant to water penetration. The cheaper
hulls
still depend on the gel coat to keep the water out

******

:-)

When one states that water is going to leak through the frp laminate
and into the boat unless it is somehow stopped by the gelcoat- and if
one means "if the hull is defective.......", then it would be best to
so state. When talking about general functions of gelcoat, laminate,
etc it would be customary to assume one is talking about a standard
hull rather than a defective one.

No builder depends on gelcoat to keep water from leaking into the
bilge.

Gee Chuck I think that's a bit of a statement. Most fibreglass
laminates are pretty porous if there are no barriers.

I'm not saying water would "flow" as such, but certainly it will seep
into the glass & definitely damage it over time.

On the other side if anyone did actually wet the layup enough that it
was truly water "proof" then it would be a very weakened laminate,
overly heavy & expensive waste of resin.

The best fix thus far is a good outer barrier usually of vinyl ester
resins in conjunction with a tissue tie layer. Even inside you need
flowcoat or such to stop the laminate being too porous from that direction.

K

I agree that fiberglass can allow water molecules to penetrate through.

There was an often referenced demonstration where somebody built a
fiberglass box, filled it with water, and bonded an air-tight top. It
sat in a classroom under daily observation, and no water was ever seen
leaking out. When the box was opened, several months later,
it was bone dry. I can't honestly say whether the box in the experiment
was covered with
gelcoat, paint, or consisted of exosed glass cloth

That's far different from a theory that gelcoat.... (which is more
porous than the laminate itself, causing the water that penetrates it
to stop or slow down when it reaches the
laminate below and hang around long enough to foster chemical reactions
that produce the gas that creates blisters)... waterproofs the laminate
to prevent leaking.

According to this observation from Pascoe's essay on blisters:

"Blistering involves only the gel coat and surface mat in 99% of the
cases. This is due to the fact that the structural fabrics, such as
roving, get saturated better. Its also because the water is less likely
to penetrate beyond the mat and, even if it does, woven fabrics do not
have the weak gel coat factor and are much too strong to allow whatever
pressure may develop within a void to cause a separation. The incidence
of blisters occurring within structural laminates is extremely small."

It would make more sense to use the structural laminate to "waterproof"
the gelcoat than to say that the gelcoat somehow seals or waterproofs
the laminate.

A vinylester barrier has proven to be extremely effective in reducing,
and in many cases eliminating, the tendency for FRP hulls to blister.

Certainly anyone can say that in 99% of cases this or that etc but often
osmotic damage is much more than cosmetic & certainly my own personal
observation confirms woven laminate can absorb moisture as much as any
other glass.

Indeed a layup that may absorb water might be better than a fully
saturated one that won't; because if it's dripping with resin it's
likely to be very much compromised strengthwise. These days where
material weight & cost demand that hulls be "designed" rather than just
follow established practice (read the old idea that thicker must be
better) then the strength of a particular laminate can be critical.

I will agree though about "blistering" osmosis or whatever label you
use, is probably more a potential worry than an actual worry. Here they
have a rejoinder about fibreglass boats "show me the documented case of
a substantial boat ever sinking due to blistering" & it's a good question:-)

K