A skirt won’t keep the kayak from sinking. If you tip over and haven’t learned to roll it back up, you’ll have to detach the skirt to get out, so the kayak is going to take on water. What keeps it from sinking is floatation that should be in the boat. This can either be in the form of sealed bulkheads or float bags that are inflated.

The skirt is designed to keep water out of the cockpit area– where you sit– so that you stay dryer (but often not completely dry). In rough water, such as whitewater, surf, and open ocean, water easily washes over the deck of the boat and you’d soon be sitting in a pool of water. On calm water, the skirt is not as much a necessity. Some people prefer them to keep small drips of water out and for insulation, but there are some recreational kayaks that have large enough cockpits where a using a skirt would be impractical or impossible.

If you’re going out in calm water and don’t want to use a skirt, that’s perfectly fine (but do make sure to have floatation either way!). If you do want to use one, make sure to practice a ‘wet exit’ drill with an instructor or experienced paddler nearby– capsize, remove the skrit, and get out of the boat.