call it a porthole, portlight,
deadlight or just plain window, making and installation them has, since
development of clear ‘plastics’ become much simpler and cheaper for
the amateur boat builder/renovator.
Much as I hate to admit it, ‘plastics’ such as Plexiglas or Lexan
are so easy to work with that using shatterproof glass is no longer a
While acrylic portlights will, unlike glass eventually get scratched
crazed, replacing them is cheap and easy.
So, the main problem for the self-builder is making sure that they
leak, especially the ones above your bunk.
whatever compound you
chose it is very important to have a clean bonding
Even finger marks will affect
But beware of using harsh
solvents and definitely do not
use acetone on plastics.
If you are re-bedding a
porthole you must remove all the
old sealant, no new sealant will not adhere to old cured stuff, even if
the same make.
It is also best if the sealant
is applied and allowed to
cure in warm conditions.
However, even with the best
modern compounds leaks can
occur due to mechanical failure.
Bedding components can pull
apart under strain, if poorly
attached, due to flexing and through differing rates of expansion
plastic and the surrounds.
plastic glazing should fit the opening with allowance for the different
expansion and contraction rates of the plastic and the surround.
And bolt holes should be
drilled oversize for the same
The amount allowed for
expansion and contraction will depend on the size of the
The larger the area of the
porthole the more you should
If replacing an old pane check
that it is a good fit
before using it as a pattern, if not make a new pattern from stiff
You can cut and drill acrylics
and polycarbonates using
ordinary woodworking tools.
For cutting there are special
blades available which are
designed for cutting plastics but a fine toothed hacksaw blade will
If using an electrical jigsaw
use a slow speed and keep the plastic cool so it does not start to
On my first attempt to cut out
a porthole with a jigsaw,
small blobs of softened plastic were cooling and resealing the cut
blade, which meant I had to go back round and cut the blobs and then
cleaning the edges.
But whether cutting by hand or
with power the edges must
be well supported to prevent chipping.
And make sure the plastic is
resting on a clean surface
to prevent scratching.
Leave the protective film on
the plastic until you are
ready to fit the pane.
Once cut, clean up the edge to
get rid of any chips or
blobs as these could lead to cracking.
Use a fine edged file and sand
It is possible to bend most
plastics but trying to put
much bend while cold can affect the integrity of the material.
Both polycarbonates and
polyacrylates can be bent using
heat but this is rather tricky.
It can be done using a heat
The problem is not to overheat
as this can cause the
plastics to got cloudy or even bubble.
The next problem is
maintaining an even heat across the
area you wish to bend.
The piece needs to be firmly
clamped and it is best to do
the heating indoors away from cooling breezes.
A simple bend can be formed
over the edge of a
For more gentle longer bends
you are really going to need
Don’t try to force the
bending, when the plastic is
ready it will bend with a small amount of pressure.
Try to keep the pressure and
the heat evenly along the
length of the bend.
The thicker the plastic the
more heating it will require,
you may have to heat both sides.
"Our voyage had commenced, and at last we were away, gliding through
the clean water, past the reeds.
Care was lifted from our shoulders, for we were free from advice,
pessimism, officialism, heat and hot air." (K.
designing portholes there are a number of things to keep in mind.
Much will depend on the style
of your boat and the type
of boating you intend doing.
If for instance you intend
sailing in all weathers at sea
you need to take into consideration the possibility of a rogue wave
into that porthole.
While most plastics are pretty
dammed strong they will
flex, so that wave hitting it may not break it but it might just flex
to break the seal around the rim.
Also the large window which
would be perfect on a
houseboat won’t fit with the traditional look of a classic motor or
And of course you don’t want
to disfigure a
beautiful wooden boat with an ugly set of portlights.
I am perfectly aware that the majority of Wooden Boat aficionados are sensible folk. However, I need to point out that I am an amateur wooden boat enthusiast simply writing in order to try to help other amateur wooden boat enthusiasts. And while I take every care to ensure that the information in DIY Wood Boat.com is correct, anyone acting on the information on this website does so at their own risk.