Have you seen the price of replacement canvas lately? Modest care and timely repairs can save you from shelling out for years to come.
If you want to keep your boat's enclosure in top shape for many seasons to come, just remember PCP. We're talking prevention, cleaning, and protection here. PREVENT costly repairs or replacement by restitching broken or loose seams as soon as you find them. CLEAN your canvas and windows regularly to prevent mildew and dirt from staining or scratching the surface. Regularly replace the PROTECTIVE finish on canvas and clear plastic "windows."
A Stitch In Time
With few exceptions, exterior fabrics on boats will be either acrylic canvas (Sunbrella or similar) or some type of vinyl-coated fabric (Stamoid or similar). Both acrylic and vinyl will outlast the polyester thread used to shape them, even more so if you use bleach for cleaning. Restitching at the first sign of thread failure avoids the need to realign and reassemble. Just pass the seams through a heavy-duty domestic sewing machine. Your selection of thread matters. White polyester, the default choice of canvas shops everywhere, suffers mightily in the sun. The better alternative is to have your canvas sewn with PTFE thread, either Tenara or SolarFix. For a DIY restitch, you're likely to find PTFE thread shockingly expensive, difficult for a domestic machine to sew, and prone to leaking at the needle holes. The DIY choice is black polyester, which costs, sews, and seals the same as white, but will last years longer due to the substantial UV protection the black pigment affords.
TIP: The discoloration that occurs where windows touch the metal of the supporting frame isn't abrasion or a chemical reaction. It's a scorch mark due to the hot metal. Keep vinyl away from the bare frame.
It's easier to prevent mildew stains in the first place than remove them. Fresh from the factory, both acrylic- and vinyl-coated canvas are stony ground for mildew. But add dirt, pollution, and bird droppings, and you create a veritable mildew garden. Vinyl canvas doesn't breathe, so condensation combined with low light makes the underside weave particularly inviting to mildew. Frequent washing is essential to keeping boat canvas bright and blemish free. A mild soap solution is best, but Woolite, or a mild dishwashing detergent, also works. Give the soap solution a couple of minutes of soak time to lift the dirt before scrubbing with a very soft brush. Rinse thoroughly, then be sure the canvas gets completely dry. Vinyl canvas enclosures need ample ventilation to keep mildew at bay.
If your canvas already has mildew stains, vinyl will usually give them up to a household spray cleaner such as Spray Nine. Vinyl canvas can even tolerate full-strength chlorine bleach for persistent stains if you limit the time of contact to a few minutes and rinse away all traces. Surfaces around or beneath the canvas may be damaged by bleach, even by strong detergent, so you may need to remove the canvas for deep cleaning. You should also recognize that anything strong enough to remove mildew stains, even a gentle vinyl canvas cleaner, is also going to strip the protective coating. The job is incomplete until you put that back, as described in the next section.
Chlorine bleach is also the only effective way to remove mildew stains from acrylic canvas, but it must be applied in a diluted state — 1 cup of bleach to 1 gallon of water. Adding 1/4-cup of soap to this mixture will improve effectiveness. Spray on or apply with a sponge and allow to soak for 15 minutes. Scrub with a soft brush, then rinse thoroughly. Smaller acrylic canvas items can be machine-washed in cold water using mild laundry detergent and a cup of chlorine bleach. As with vinyl, deep-cleaning acrylic canvas strips it of its protective finish.
TIP: To keep zippers free and easy to work, simply move the zipper every few weeks. That will keep the salt and dirt from hardening and jamming up the zipper.
Sealed To Last
Here's the important part. If you want your canvas to last, you have to replace the protective finish lost to sun, weather, and washing. This is the step too many boat owners skip. The top coat on vinyl serves three essential functions. It seals in integral plasticizers. It shields the surface from soiling, abrasion, and, if a sunscreen is included, from UV damage. This coating sacrifices itself first to the damaging effects of exposure and cleaning. If you fail to maintain the coating, the vinyl bears the damage instead.
The makers of Stamoid recommend the Imar Stamoid brand of protective cream and spray used in tandem. The single-application alternative recommended by most other vinyl manufacturers, fabricators, and many boat owners is 303 Aerospace Protectant. Whatever product you use, applying it every couple of months and after washing with soap or detergent will keep your vinyl supple and healthy for years.
Acrylic canvas needs a different topical application. The finish applied at the factory to improve water and stain repellency is lost over time to cleaning and exposure. Sunbrella has long specified 303 Aerospace Fabric Guard (NOT 303 Aerospace Protectant) to restore repellency. A single annual misting (two coats) can be adequate to counteract the loss due to exposure, but you must also treat the canvas after deep cleaning. Fabric Guard can damage vinyl windows, so apply in still conditions, taking care to shield plastic windows from any overspray. Given the cost of replacement canvas, substituting a waterproof product intended for tents, sofas, or wood decks because it's cheaper can be false economy.
Caring For A Polycarbonate Boat Windshield
"Bulletproof" is what probably pops into your head when someone mentions polycarbonate, or Lexan — the best-known brand — but what a boater should think is "sunburn." Polycarbonate is not UV stable. If your rigid clear plastic has taken a yellow tint, it is polycarbonate, not acrylic. Polycarbonate has a relatively soft surface that a rubber squeegee, a dry cloth, or even a wet paper towel can scratch.
Care requirements for polycarbonate are more like those for vinyl than acrylic. It needs to have plasticizers sealed in with frequent applications of a UV protectant. Polycarbonate is more tolerant of detergents but not of alkaline cleaners, so stick with soap and water.
Scratches and surface oxidation will yield to the same treatment as acrylic except that the grit range for wet sanding is 1,000 to 3,000. However, the only polycarbonates really suitable for exterior boat applications will have a factory-applied coating that gives the plastic a harder surface and provides UV protection. Unless your polycarbonate is already yellowed or dulled with oxidation, do not polish it as this will remove the protective coating. Because of the innate susceptibility of this plastic to UV damage, the regular application of a UV protectant, even on UV-stabilized polycarbonate, will help to maintain its clarity.