Exposure to a marine environment causes rapid deterioration of natural fibers in boat seats. This makes the thread in boat seats dry rot and break before the synthetic marine vinyl fabric does. Removing the upholstery is time-consuming and is usually dirty work, so the easiest way to sew the loose seams is without removing the seat covers. This makes hand-sewing them--using a hidden or slip stitch with a curved upholstery needles--the most convenient repair option.
Cut a piece of thread that is between 18 inches and 3 feet long. Do not cut the thread longer than 3 feet because long threads tangle easily. Make sure one end cuts neatly with no dangling strands or frayed spots--this will make it easier to thread the needle.
Push the end of the thread through the eye of the curved hand sewing needle. Bring the two loose ends of thread together and tie them into a knot.
Hold the seam slightly open and push the pointed end of the curved needle behind the fabric so the knot will be on the back of the fabric when the needle and thread are puled through the fabric.
Pierce the first empty spot the original thread went through and pull the needle and thread all of the way through.
Push the point of the curved needle into the hole straight across from the one you just pulled the thread through. Before pulling the needle all of the way through this time, push down on the back end of the needle so the point pops through the next hole. Then pull the needle and thread all of the way through.
Repeat Step 5 over and over until the length of the ripped seam is sewn shut. This creates the stitch known as a hidden stitch, and it will not be obvious that the boat seat was torn and has been sewn.