Choosing fabric for your dinghy chaps is the same as choosing fabrics for all other exterior canvas projects on board. You want something that is both abrasion-resistant and UV-stable. A heavy-duty marine canvas like Sunbrella is purpose-made for just such projects. It is solution-dyed to prevent colors running or fading, and is shrink-proof, stretch-free and easy to work with. It is woven to be water-, mildew- and stain-resistant and, perhaps most important, is rated to block 98 percent of damaging UV rays. All these features mean your finished project will not only fit well and look great, but you can count on it to stand up to years of use and abuse. Sunbrella is available in a wide spectrum of weights, but the best choice for this project is the standard marine awning fabric, which is a 9.25- or 10-ounce cloth.