I have installed exterior mounted plexiglass (acrylic) windows on
two of my boats - a 1973 Venture 224 which I used to own several
years ago, and on a Tanzer 26 (a 1975 model with the same
windows as the Tanzer 22). The Venture 224 (a MacGregor 25) had a
single long deadlight (a non-opening window) on each side of the
cabin, similar to what is found on the more recent Tanzer 26 models. [See the photos of these boats at the end of the article.]
With the Venture, I updated the look of the boat by designing and
installing long trapezoid shaped windows. There was considerable
overlap with the original window openings, but the new shape did
give the boat a modern appearance. On the other hand, with the Tanzer
26, I simply used one of the old aluminium frames as a template for
the new plexiglass windows (I added an extra 1/8 of an inch all
around just to be safe). Regardless of the window shape you chose
for the plexiglass, I do not recommend modifying the actual window
opening in the boat's cabin walls. This could affect the structural integrity of the cabin and deck, and it would probably make it more difficult to obtain a nice finish for the interior installation of the new windows.
With both my boats, the overlapping plexiglass windows were applied
directly to the fibreglass exterior cabin walls with a high quality
sealant and round headed screws (or round headed bolts and nuts). I
completely discarded the old exterior aluminium frames. Over the
years these frames had been so heavily caulked, and re-caulked, that
they were almost impossible to remove without bending them into
pretzels. Even with the use of the sharpest razor blade knife I
could find, it took me close to two hours to remove one of the frames
from my Tanzer 26 without bending it completely out of shape. (I needed one for a
template). The removal of the other 7 frames was relatively quick -
they came off with extreme prejudice.
Whatever you do, be sure to carefully remove and save any interior
aluminium frames. These will probably be held in place only with screws
(and very little caulking). You'll need to reinstall these
afterwards for a nice finish inside your cabin.
On my Tanzer 26, I screwed the plexiglass windows in place on the
exterior cabin wall with the same holes used for the aluminium
frames. Since Tanzer manufactured my boat with plywood backing
around the window openings (the core between the fiberglass cabin
wall and the interior liner), I was able to use screws to install
the new windows. Without this wood backing, I would probably have
had to use bolts and nuts to hold the windows in place. This is the
technique I employed with my Venture 224, and it is a little more
costly and time consuming. Whatever the case, be sure not to overly
tighten the screws or bolts or you'll risk cracking the plexiglass.
I used stainless steel 3/4 inch #8 screws. It's worthwhile to get
the phone book out and shop around for the best prices when buying a
large volume of stainless steel fasteners. I needed a box of 100
screws, and I found prices varied considerably, even among suppliers
servicing industrial needs.
The biggest secret with this type of project is to have your
plexiglass supplier do all the tricky work that goes into
manufacturing the new windows. In other words, the supplier will cut
the windows to shape and drill uniformly spaced holes (2.5 to 3
inches apart, or spaced to match the aluminium template). Also ask
them to bevel and polish the outside edge around the windows. Note
that depending on the shape of the windows (e.g. trapezoid shaped
windows), the bevelling will have to be done on the opposite edges
when making port and starboard windows.
Costs? Even with all the work that went into making my eight
plexiglass windows, they only cost me $120 Canadian (less than $90 US). And I
could have probably saved a few bucks by shopping around. See the phone book for plastic suppliers in your area.
I have had good results using the darkest smoked plexiglass
available. The dark colour will hide the outline of the window
cutout on the cabin wall, but dark plexiglass always looks much
lighter when you are inside the boat looking out. I chose to go with
plexiglass with a thickness of 3/16 of inch, although 1/4 inch is
also an option. It's interesting to note that the original
plexiglass on my Tanzer 26 was only 1/8 inch thick. My plastic supplier
also stated that 1/8 inch thick plexiglass is all that I would need,
even though he had no information on the thickness of the
original windows. However, for appearance purposes, he recommended
3/16 plexiglass.
I used black 3M Marine Adhesive Sealant 5200 to caulk the windows in place, although people may wish to consider using a product which provides for a less permanent bond (to make it easier to remove the windows at a letter date).
Black is the colour sailboat manufacturers tend to use when
installing these types of windows at the factory. Black sealant also
hides itself well under the dark smoke plexiglass. The only problem
with black caulking is that it is very noticeable if it oozes out
past the window edge as the plexiglass is pressed against the white
cabin wall. This can be difficult to control - for starters, try a bead of
caulking a little less thick than a pencil about 1/2 inch from the edge
of the window. This has to be applied smoothly and, as much as possible,
in one continuous flow. This is not always easy when working with a manual caulking gun. Experiment a little before starting with your first window.
Note that the sealant should be applied to the back of the window,
and not the exterior cabin wall. And you should also have the screws
or bolts ready as you press the caulked windows into place. Needless
to say, this aspect of the project is definitely a two person job.
It is also wise to prefit all windows before proceeding with any
caulking. Once you get going, it doesn't take too long to fit the
windows in place. My wife and I installed eight windows on our
Tanzer in about 2.5 hours.
One word of caution about the installation of plexiglass (acrylic)
windows. It's important to have your plastic supplier drill slightly
oversized screw holes in the plexiglass windows (the caulking will
fill in the small gap). This will allow the windows to expand or
contract under the hot summer sun or in freezing winter
temperatures. Otherwise, there is a chance your windows could crack
after a year or two.
Boat sag could also lead to stress on windows which could cause them to
crack. I had this problem with my Venture 224. I had installed
5 foot long trapezoid shaped windows on the boat while it was in
the water. Two years later I noticed a vertical crack down the
middle of one of the windows (everything was perfect up to this
point). The boat had been sitting on its factory made trailer all
winter. I could tell this crack was caused by the boat sagging on
the trailer because when I launched the Venture, the crack closed up
so tightly that it was almost impossible to detect (and it didn't
leak any water). But I don't think this is much cause for worry with
the solidly built Tanzers - especially with shorter windows.
And finally, a word about plexiglass (acrylic) and Lexan. Plexiglass
is relatively cheap and scratch resistant, but it can crack if
stressed the wrong way. Laxen is very strong (sometimes referred to as
bullet proof plexiglass), but it is relatively expensive and has a
softer surface which scratches easily. Unlike plexiglass, heavy duty
buffing and polishing can never fully restore
a clear finish to lexan once it has been scratched or becomes dull with age. On the other hand, there's little need to worry about your windows cracking when using Lexan. Moreover, I suspect bolting on 1/4 inch lexan windows would add
to the strength of the boat's hull and cabin
structure, although I do not believe this is necessary with the Tanzers.
Good luck.
Photos of boats with Updated Windows
The new plexiglass windows on the Tanzer 26 I used to own (a 1975 model).
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The trapezoid shaped windows I installed on my old Venture 224 (MacGregor 25)
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Photos and article by Michael McGoldrick.
© Michael McGoldrick, 1997.
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