Ready for some shade or rain protection? Then it's time for a canvas enclosure. This upgrade consists of a frame that supports many complementary parts: fabric or vinyl, window technology (also referred to as “the clear”), and threads and fastening systems to connect all the pieces. You will want to do your homework and choose wisely, because a new enclosure can not only make a huge difference during a day out on the water, but can also impact the value of your boat.
Fabric and Vinyl
The non-transparent portion of an enclosure is made of fabric or vinyl, both of which have made advances in recent years. Materials differ in aesthetics, including colors and textures, and also in breathability, water resistance, durability, UV resistance, longevity, suppleness, warranty length, and dimensional stability (which is its resistance to stretching and sagging). The choice of ideal material depends on the application and the objectives of the project.
The traditional option has been Sunbrella, which is a solution-dyed acrylic fabric developed as an alternative to cotton. Sunbrella is a durable material that’s water-resistant and breathable, so it’s especially good for high-precipitation areas like the Pacific Northwest.
Today, there are four standard types of outdoor Sunbrella, starting with the basic, which comes in over 30 colors and carries a 10 year warranty. Next up is Sunbrella Plus, which adds a urethane coating for greater water and abrasion resistance. Sunbrella SeaMark combines acrylic fabric and Haartz textured marine vinyl to create a nearly waterproof fabric, and Sunbrella Supreme uses a urethane to adhere “flocking” to the back of regular Sunbrella. This creates a rich, velvety feel, in a contrasting color to the opposing side.
An alternative to fabric is vinyl, like Serge Ferrari Stamoid, Weblon, and others. The vinyl is coated woven polyester, which has high dimensional stability and is both fade-resistant and completely waterproof (rather than water-resistant like fabric). That means it doesn’t breath well, but it does provide a nice, non-permeable finish that’s easy to clean.
Other brands of materials include the fabrics Riviera Herculite, Top Gun (woven polyester coated on both sides to add water resistance, but slightly less colorfast than Sunbrella), and Odyssey III, a lighter and more affordable version of Top Gun.
Once you’ve decided on a body material, it’s time to review the options for windows in the canvas. There are two major types: clear flexible polyvinyl sheeting that is rollable, and semi-rigid polycarbonate or acrylic windows, which will bend to varying degrees but will not roll. Clear materials come in different thicknesses and generally the thicker the material, the more durable and the longer it will hold its shape. Roll-vinyl comes in 20 to 60 mil (a mil is .001”), but most shops use at least 40-gauge because thinner material will not yield the best results. Flexible vinyl is susceptible to shrinkage when it’s cold, and both the material’s suppleness and fit can change depending on temperature.
Polyvinyl is used on curtains that need to be open to allow access or air flow. Most of the canvas shops I spoke with use Strataglass, which has a coating that blocks approximately 98% of UV rays, is more scratch-resistant, and has good dimensional stability. Crystal Clear 20/20 is Strataglass' press-polished vinyl, which is popular for its clarity and is available in tints including clear, light smoke and dark smoke. Isinglass has fallen out of favor, although if you put Strataglass and Isinglass next to one another when they’re new, they look very similar. The difference is in the way they age, which includes various degrees of hazing, yellowing, and peeling.
Semi-rigid windows come in 40 to 80-gauge polycarbonate or acrylic versions, have a glass-like clarity, and hold their shape extremely well. These windows are somewhat flexible so you can bend them around corners or push them up to hinge open, but folding or rolling isn’t an option.
Polycarbonate windows are coated with a UV-blocker that also makes them scratch-resistant, but if you do damage one, the coating can’t be buffed out. Polycarbonate options include Rainier Diamond Windows (virtually shatterproof, with 250 times the impact-strength of glass, and 30 times that of regular acrylic) and Makrolon. Makrolon can be stitched to fabric and opaque vinyls, while Rainier must be bonded via a special proprietary process.
The modified acrylic versions of semi-rigid windows include Rainier Crystal Windows, which are 10 times more resistant to breakage than regular acrylic. EZ2CY is another brand of acrylic which boasts little distortion and good performance in the sun—but it carries a hefty price tag. Unlike polycarbonate, acrylic will break if it’s bent too far. It offers some UV resistance without additional coatings and isn’t as scratch-proof as polycarbonate, but when it is scratched or scuffed, it can be polished out. Rainier has to be bonded, while EZ2CY is glued.
Rigid material comes in sheets rather than rolls. Like rollable vinyl, longevity increases if the windows are covered when not in use. Fabric or vinyl, or a vinyl-based partially transparent mesh cover, can be used for protection and can double the clear curtain's lifespan. Mesh has grown in popularity because it offers privacy and shade, while still allowing you to see out when others cannot see in.
Zippers, Tracks, and Fasteners
With the clear and the solid chosen, sections of the enclosure have to be made with zippers, slides, and fasteners, all of which serve well in specific applications. Zippers do the grunt work in an enclosure by opening sections for ventilation and access, but putting zippers in corners is a no-no. Not only can they obstruct the view, but zippers can fail in these high-stress areas.
Zippers should be sewn with an outside flap cover for clean looks and protection from UV damage, salt, dirt, and oxidization. Zippers need to be cleaned and worked, so it’s imperative to flush them with fresh water and zip and unzip them at least once a month, even in sections you don’t open often.
Without regular attention, zippers freeze up and have to be cut out of the enclosure and replaced. Most canvas shops also recommend that you lubricate the zippers after you wash them. Products like YKK Zippy Cool are best, but in a pinch you can use wax or even ChapStick or sunscreen.
To connect those sparkling semi-rigid windows to the boat itself, stainless-steel or plastic slides or snaps are mounted to the boat. Tracks are available in single, double or triple versions that have evolved with the use of UV-resistant materials. Snaps also work, but they will need regular lubrication. And if you’ve ever had to stretch canvas while trying to get snaps, zippers, or slides to meet, you’ll appreciate twist lock fasteners. These are a surefire way to get two tight sections to meet.
When it’s time to put it all together, the key will be the thread—which has traditionally been very susceptible to UV damage and can be a weak link in the whole design. Depending on care and exposure, conventional polyester, nylon, and cotton thread commonly used by canvas shops can last four to six years before it fails.
New technology includes polytetrafluoroethylene (PTFE) thread, which is the chemical name for Teflon from DuPont. Some brand names include SolarFix, Helios, Profilen and Gore-Tex Tenara, all of which resist stretching, fading, staining, chemical exposure, and sun damage. Some manufacturers warranty it for a lifetime and it comes in a variety of colors including clear. This thread does have some tradeoffs, not the least of which is that it can be quite expensive and it doesn’t hold up to chafe well. The thread also doesn’t absorb water, so it doesn’t swell, and therefore can create larger holes in the stitching which can cause your enclosure to weep. Some shops will use Teflon thread only in the sides and not the top, so ask about your fabricator’s philosophy.
There are numerous new materials available today and a new enclosure will make your boat seem new as well. Now, it’s just a matter of collaborating on the design with your canvas fabricator that will best enhance the way you use your boat.
For information on how to maintain marine canvas, see How to Clean and Care for Isinglass and Canvas.