On 30/10/14 13:05, Ed Huntress wrote:
On Thu, 30 Oct 2014 17:46:39 +0700, John B. Slocomb
wrote:

On Wed, 29 Oct 2014 10:10:39 -0400, Ed Huntress
wrote:

On Wed, 29 Oct 2014 18:46:24 +0700, John B. Slocomb
wrote:

On Wed, 29 Oct 2014 06:37:26 -0400, Ed Huntress
wrote:
snip

Anyway, your sarcasm was misplaced, as was Richard's. I don't know
what the hell he was talking about regarding boat paints. And when you
popped off about PFDs, it was clear that you don't sail where we sail.

I think Richard was probably referring to the fact that most, if not
all, small production fiberglass boats have the hull finished with gel
coat and a boat requiring paint would be one on which the gel coat had
deteriorated to a considerable degree.


Enjoy your sailing in S.E.A., John.
Cheers,
John B.
It's true that failing gel coats on lightly-built fiberglass boats may
reflect fatigue in the hull layup, but I don't see that as a reason to
make a blanket statement about it. Strongly-built boats, like a Boston
Whaler, Black Watch, Cape Dory or Stone Horse, will FAR outlast their
gel coats, and it has nothing to do with fatigue -- because those
boats generally don't fatigue.

In tropical countries it is quite common to see old fiberglass boats
with "chalky" finishes due to UV deterioration.
It's the same here on the mid-Atlantic coast.

While this may or may
not be a serious problem depends on the individual case but the
turning up of the nose at fiberglass boats that need paint is
certainly not a frivolous notion.
It depends. But it's not accurate to make a blanket statement about
it. Eventually, even well-built boats need a new coating of some kind.

There's an entire industry dedicated to re-covering those boats. It
satarted with a spray-on replacement gel coat around 1960; progressed
a few years later to sprayed-on two-part epoxy; and, finally,
developed into re-coating with two-part polyurethanes, a lot like the
paint used on high-class custom cars.
Ed, I think in this case you really don't have all the facts. I've got
a good friend in the business and certainly he will re gel-coat your
boat for you, but it costs far more money than a two part polyurethane
paint job
Spray-on polyester get coat is a lot cheaper than two-part
polyurethane -- somewhere around 1/3 the cost. There are quality yards
throughout the Northeast that will replace a gel coat with a new
sprayed-on polyester gel coat.

But then it's a matter of how good you want your finish to be.
As-spraryed, polyurethane is done. You can't rub it out without
ruining its durability, but, if it was done right, you don't have to.
(The one-part acrylic polyurethanes can be rubbed out, but that's a
different material.)

Gel coat, on the other hand, generally looks lousy, as-sprayed. It has
to be levelled and rubbed out. It can require a lot of labor, which
will raise the cost above the cost of a polyurethane finish.

, which is not necessarily "similar to paint on high class
cars" as in many cases it is the same stuff. Dupont Imron comes to
mind.
Yeah, it often is the same stuff. Others are similar. I haven't seen a
car painted with Interlux, but then, I've never asked. d8-)

And polyester gel coats are porous; they can get stained, or marked up
badly because of the way they were tied up at a dock.
If "Polyester gel coats" are porous then so is the whole hull as
"gel-coat" is commonly just polyester resin with an added pigment.
It is porous; water enters through diffusion and by capillary action:

http://tinyurl.com/nmxdnlk

And the more styrene there is in the resin, the more porous it becomes
over time. Cheaper boats generally have more styrene in the resin.
Polyester resin is permeable, even without styrene. Epoxy is much less
so. Likewise, polyurethane.

It's not widely appreciated how much this degrades the interlaminar
strength of polyester-resin composites.

There are more additives in polyester gel coat than just pigment, for
scratch resistance, UV protection, and so on.

Gunner is more likely talking about rolling on a coat of house paint
g, but I don't get why Richard was so dismissive about painting a
boat. There are a lot of boats around here right now that are dry
docked or up on stilts, having their topsides painted at the same time
they're getting a new coat of bottom paint, before the weather gets
too cold. Most of them are fiberglass boats.
I suspect that it is because properly painting a deteriorated
gel-coated hull is an expensive proposition as to do a good job you
first need to remove the old gel-coat down to a smooth solid surface
and removing gel-coat is a pain in the butt and pains in the butt tend
to be expensive. Additionally, I suspect, it may well be extra costly
in the U.S. due to your environmental laws. I read somewhere that a
U.S. yard had refused to allow removing old copper bottom paint as
they said it would get them in trouble with the environmental people.
We don't use much copper bottom paint anymore, largely for that
reason. Bottom paints now are usually *very* specific to the regional
waters one will sail in. I got away without bottom paint for a whole
year by sailing my little Cape Dory Typhoon up a freshwater creek once
a week. It killed everything growing on the bottom.

I expect the stuff my dad made up in the early 1970s would be frowned
upon these days and classify the boat as HAZMAT. He had made a 26'
Alaskan salmon dory when we lived in Huntington LI NY and the first year
when it came out of the water for winter storage there were quite a few
barnacles even with the antifouling paint. The hardware store owner
where it was being stored said not to bother with off the shelf stuff,
even the good stuff, but make your own and gave my dad the recipe which
was a cheap antifouling paint base with some added industrial strength
disinfectant that you could buy in vials in town, and powdered copper.
The next year when it came out there were no barnacles. Might not have
been much sea life near where it was moored but Huntington harbour was
pretty contaminated at the time anyway.