By Tim Melville

In my charter business, we spend thousands of dollars and countless hours on upkeep. To this end, our 20-boat fleet provides the perfect base for torture-testing maintenance products for DIY readers.

Home port for Bosun's Charters is Sidney, British Columbia, on Vancouver Island. Our region is known for soggy weather and last year was a wetter-than-usual season. While the rain hampered boating somewhat, it provided the ideal lab for testing canvas water repellents. We received five products for testing. Four arrived together: Aqua-Tite Water Repellent, Captain Phab Water Repellent, Iosso Water Repellent and Natural Marine Boat Top Waterproofer. The fifth product, Watershedz, arrived a month later and was evaluated separately, though we've included it in our results here. Four of the products are petroleum-based distillates, two contain silicone; Iosso is the only biodegradable product. All but one come in a spray bottle Captain Phab arrived in an aerosol can.

The water repellents were applied to black, blue and red acrylic sailboat dodgers and the results were monitored during a three-month period. We also coated the blue acrylic top on our chase boat with each of the four products. This acted as our control panel, allowing us to carefully compare each product's performance over eight months. The covers ranged in age from three to eight years old and were in varying stages of wear.

We applied the first four products one day in early July to clean, dry canvas though, aside from removing dust and dirt with a brush, no extraordinary cleaning was done first. Dividing the top on our chase boat into quarters, we applied one mixture to each section and also to one of the test dodgers according to the directions on the bottles.

Aqua-Tite contains silicone and mineral spirits and can be sprayed (which we did), brushed or rolled. It's a strong-smelling solution that soaks in quickly when sprayed on and covers well.

Captain Phab comes in an easy-to-use aerosol spray can but, like all aerosols, the can must be held upright as it empties. This made it extremely difficult to control overspray, especially when coating flat surfaces. The mixture smells strong and soaks in well. The company now offers a bottle with a trigger spray which we highly recommend for coating fixed (i.e. mounted on the boat) canvas.

Iosso is the only non-toxic repellent of the five we tested. It's also odorless, which we liked. Coverage is difficult to control, as the spray nozzle squirts the liquid in a stream rather than a mist. The solution pools on the fabric and runs off the surface, especially in vertical or sloped areas. We switched to a different nozzle that sprayed a mist but the product still pooled on the surface and didn't soak readily into the fabric. On the first heavy rainfall, water beading was inconsistent some areas repelled water better than others due, perhaps, to the inconsistency in application.

Natural Marine Boat Top Waterproofer is another strong-smelling mixture that contains 12% silicone. The solution flows well, quickly soaks into the fabric and provides even coverage.

Watershedz was tested in August, six weeks after the other water repellents. Following the directions, we applied one light coat from a small sample spray bottle. A hydrocarbon distillate, the product produced a strong solvent smell that was not unpleasant and one coat provided excellent coverage.

All five products dried to a clear finish and none changed the color of the fabric. The strong odor of the petroleum-based products evaporated in a few days. Except for Iosso Water Repellent, these products can cause skin irritations, so you should wear rubber gloves and eye protection during application. Avoid breathing fumes and, if you're not applying the repellents outside, you'll need to provide good ventilation.

In the beginning,the "just-waxed" look of the tops made it obvious that they'd been coated with water repellent, but the effect quickly diminished with time. Five weeks after application, Aqua-Tite, Captain Phab and Natural Marine performed about the same in a heavy rain – the water would bead on the flat surfaces and run off. Ditto, for Watershedz. The exception was Iosso. Its biodegradable properties certainly benefit the environment, but it was not as effective as the stronger-smelling petroleum-distillate products. At this stage, there was no beading and water soaked the fabric where it pooled in flat areas, though it didn't soak through.

By late September, all tops showed a definite loss of effectiveness. After a prolonged rain, there was no water beading on the dodger coated with Aqua-Tite; the fabric absorbed water but didn't leak. On the Captain Phab dodger, water would still bead. The flat areas absorbed water but didn't leak. The Iosso dodger soaked the fabric but, again, the fabric didn't leak. Water was still beading on the cover coated with Natural Marine and with Watershedz, except on the flat surfaces which were just beginning to soak in.

By mid-October, all the dodgers absorbed water but none actually leaked, and all were removed for winter storage. At this stage, Watershedz, the late entry, performed at least as well as the others, allowing for the time delay. Our chase boat remains outside with the top up and, eight months after application, there is no apparent difference between the four coated sections rain soaks into the fabric and it leaks where the water pools.

While there are slight differences between the water repellents, our test results indicate no clear, long-term winner. Watershedz gave the best coverage a light coating delivered comparable protection, so we used less product. Natural Marine was the easiest to apply and also provided good coverage.

How long will a water repellent last? Recoating depends on a number of factors: the porosity of the fabric, UV exposure, abrasion from salt and other airborne particles, fabric flexing, freezing and thawing, precipitation and washing which quickly reduces the effectiveness of any water repellent. None of the products we tested provided instructions on how often to reapply. DIY contacted the manufacturers for comment and they unanimously recommend recoating every season.

Considering the results of our test, I suggest you recoat when water no longer beads and is absorbed by the fabric, but before it starts to leak. For boaters on the West Coast who leave their canvas on year-round, that means every six to eight months.

Tim Melville and his wife Vicki operate Bosun's Charters, a 35-year-old charter company located in Sidney, B.C., near Canada's Gulf Islands and the U.S. San Juan Islands. The company offers bareboat and skippered charters, learn-to-sail vacations, flotillia cruises and yacht management on power and sailing yachts ranging in length from 8.1m to 12.6m (27' to 42').