Re: Plexiglass

amelliahona <no_reply@...>

Hi Tom & Kirstin:

I am an certified aircraft mechanic (among other things) and we deal with plexiglass
a lot as most aircraft windows are plexiglass. You don't post whether the scratches
are on the surface of within the substance of the material but there is a difference.

In my experience the majority of the scratches we have on our Amel SM2000 Hull #
335 are surface scratches. These arose when we left our boat in Antigua with the
Amel supplied window cover on and the Montserrat volcano spread ash over the area.
The abrasive ash got between the cover and the plexiglass and as the cover flapped
in the breeze it upbraided the window. Those types of scratches can be polished
out. Hand polishing is best. You can go online to and search
for a "micromesh" kit. It comes with all the components needed to treat a couple of
windows, but be prepared to spend hours and hours doing this. If you use power
tools to do this you need to use lots of cooling water and low speeds so that heat
build up on the window won't distort the optics. We now place terri cloth covers
between the window and the window cover and that has mitigated the entrance of
dirt and abrasive grit when the boat is stored.

More common than the above is what is called crazing. This can be on the surface
but is also deep within the matrix of the plexiglass. It first appears as small
spicules or pin point dots that are seen when the sunlight strikes the window at
a particular angle. It can then over time progress to long scratch like appearing
"craze" marks within the plexiglass. It seem nobody really knows why this occurs
but it is thought to be induced by heat, stress, and UV and is probably some sort
of crystaline change in the molecular structure of the plexiglass. The only cure
for bad crazing is replacement as it is deep within the matrix of the plexiglass
and no amount of polishing will work. Preventive measures include keeping the heat
down (i.e. covering the window with airspace between so that there isn't heat
build up in the window) , minimizing stresses (not stepping on the windows and
avoinding rogue waves from crashing upon them) , and shielding the window
from UV (i.e. using a cover when the boat isn't being used. All of those things
are hard to do on boats and airplanes. So we just resign ourselves to replacing
those windows periodically. Fortunately the boat windows are cheap compared
to the airplane windows. My last set of aircraft windows (2) cost me around

Lastly, there are special techniques for cutting and drilling plexiglass and I
would agree that you can do your own for relatively little money. I think if
you do some searching on the internet you will find the necessary skills. If
not call Aircraft Spruce and ask for their instructions on doing it.

All the best, Gary Silver

--- In amelyachtowners@..., "Thomas" <thomas.kleman@...> wrote:

Don't know the source of the damage (new boat to us) but our plexiglass in the cockpit is scratched/damaged in places. Looks like either UV or someone went crazy with an abrasive compound. Anyone have a source for replicating the four pieces ? I asked around my marina and was shocked at the prices I heard.

THX- Tom and Kirstin on L'ORIENT SM2K #422

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