Posts tagged acrylic

Question: Sealing Boat Windows

One of the sailors prepping for this year’s Singlehanded Transpac recently asked me how the windows on Idefix held up. As you might recall from this post, in preparing for the 2012 SHTP I had replaced the old, leaky, cracking and hazy windows with new ones. I didn’t go into much detail about how I installed them, and I hadn’t followed up on how they held up, so it’s probably time I answered that.

Just one word: plastics

acrylic_sheetsFirst of all, I used acrylic for the windows. Acrylic is also known as plexiglas. The other choices would be polycarbonate (sometimes referred to as Lexan) and glass. Glass is an obvious no-go for me because it’s heavy, fragile, expensive, and hard to cut and shape. Polycarbonate is frequently used to make bulletproof windows, fighter pilot canopies, motorcycle helmet visors, and other impact-resistant applications, so one might think it would be a good choice for a boat window. But it has some significant drawbacks. For one it scratches much more easily than acrylic. It is also way more flexible for the same thickness. And more expensive. Finally it is very hard to find it in the right thickness, and colors are very limited.

Acrylic, on the other hand, is quite stiff and scratch resistant. The downside is it tends to crack if it is improperly stressed. In the end, I chose it for the simple reason that it was cheaper, easy to cut myself, which is why all the boat manufacturers use it for windows and hatches.


Cutting the acrylic to shape was pretty easy. It comes with a protective layer on each side that you peel away before installation. I removed the existing windows and used them as templates, tracing their outline on the protective sheeting. I then cut the acrylic using a bandsaw, and smoothed the edges with a belt sander.

The goop

795After choosing the material, I had to choose a way to fasten it to the boat. The Olson’s original acrylic windows were fastened with screws every 6 to 12 inches, and many had cracks radiating from them. The reason they crack is that the windows expand and contract much more than the fiberglass does with changes in temperature, leading to loads at the screws. I didn’t like the idea of drilling holes into my spiffy new windows, so I decided to forgo the screws, and just glue them on. Many boatyards take this approach. For adhesive, I did a bit of research on boat forums and chose Dow 795, which is allegedly used for gluing windows into skyscrapers. I’ve been told that Sikaflex 295 UV will work as well.


First of all, I had to meticulously clean up the area around the old windows. I hate leaky boats, and I wanted a perfect seal. This required a fair bit of peeling off old 4200 (yuck), scraping it off with razor blades, and sanding whatever was left. Then I rubbed the bond surface with acetone and wiped it dry. When all was ready, I cut the protective sheeting on the acrylic with an exacto knife in such a way as to expose only the bond area, leaving the inside window protected. I applied a steady bead of 795 all around the window. Too little and it will leave voids, but too much and it will ooze all over the place. Then I lined up the window and pressed it into place. The hardest part is to find a way to apply pressure to the window to keep it lined up and in place while the silicone cures. This involved a clever arrangement of 2x4s against the lifelines, but the forward windows were tricky and I ended up holding them in place manually for a little bit, then leaving them to their own devices. The cure time for 795 is supposedly three weeks, and I was a little worried because we had our usual Seattle cold and humid weather, and I even took the boat sailing a few times, but eventually everything hardened up nicely and the windows stayed put.

New hotness.

New hotness.

Ten thousand miles later…

As it turns out, the windows worked perfectly. There were no leaks for my whole trip to Australia, and the windows were nice and solid. Either at the dock or on the trip, one side of the boat was a little more exposed to sunlight, and one of the windows ended up getting a little bit of UV crazing, but other than that they looked as good as new.

And finally, a question of my own. What do you call the windows on a boat? Portholes? What if they don’t open?


With all the free time I have now that the boat is in the water, I’m finding myself quite bored. Luckily I can always find something to do on the boat. Changing out the leaky, cracked old windows, for example. A couple sheets of acrylic, a bandsaw, some Dow 795, lots of masking tape, and voilà! – new windows! Without the screws, these will never crack – theyl’ll probably fall off instead.

Old and busted.
New hotness.

The Front Door – Part 2

We had a weekend of February summertime weather this weekend, so I spent it working on the boat and finally finished a project! It’s not much, but it makes me feel good, and looks really cool. I present the finished companionway board, complete with locking handle (OK, so I don’t have the stopper on the boat to make it lock yet, but that’s totally, like, a 5-minute job).

New super sleek board in place.

I’m pretty excited about being able to see out into the cockpit from inside the boat!

The view from inside isn't bad either.

The Front Door

Perfect fit.

Another item I’ve been working on is a new companionway board. I felt that I needed to replace Idefix’s two little companionway boards, which don’t close very well, with something a little more solid, that I can insert quickly and lock in place securely. So I took a lot of measurements and bought a big piece of dark transparent acrylic. I then discarded all my measurements and just traced the outline of the old boards on the acrylic’s protecting sheet, and cut it with a bandsaw. After a bit of sanding, it fit perfectly. Now all I have to do is install a handle from an old, broken Lewmar hatch (came with the boat), and peel the cover off. The unfortunate thing with acrylic is it’s heavy and expensive, but I feel it’s worth it. I’m rethinking my idea of making a transparent acrylic nav station cover though…

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