A spraydeck is a sheet of water-tight cloth (for example, rubberized or impregnated cloth) cut out to fit over the opening, or cockpit, of the boat or kayak. It is removably fastened to the rim surrounding the cockpit with a line or elastic string. The line or string runs in a hollow seam along the edge of the spraydeck, and is tied around the rim or stretched over it. It is important that the fastening be secure and yet quickly releasable if the boat should capsize, so that passengers can get away from the capsized boat.
A spraydeck has a cut-out hole for each passenger. Each hole may likewise be encircled by a line or elastic string running in a hollow seam on the edge of the hole. This makes it possible to tighten the spraydeck around the body of the passenger.
In hard weather with high sea and when paddling on whitewater, the spraydeck prevents breaking waves from filling the boat, which is why it is an important piece of safety gear. When it rains the spraydeck also keeps the lower body of the passengers dry and prevents rain from building up a puddle at the bottom of the boat. This is neat, but not as important as the safety function.