Blow up your inflatable boat.
Mix 1 tsp. of dish soap with 1 qt. lukewarm water to create a soapy solution. Sponge the soapy solution over your boat to determine where the seam leak is. Watch for the soap solution to bubble when it hits air and mark this location using masking tape. This is where your leak is. You may have more than one leak, so test the whole boat.
Cut a round patch that's 2 inches larger on all sides that the seam hole. Use the right fabric for your boat, such as PVC, vinyl or hypalon. Cut as many patches as you need.
Wash the exterior of your boat three times with a solvent that works for your boat. Methyl ethyl ketone, available at hardware stores, works for PVC boats. Scrub the boat and the patch with a rag and wait for five full minutes. Apply the solvent again, wait five full minutes and apply one last time and again wait five minutes.
Mix your glue and accelerator while you wait for the solvent to dry. The ratio of glue to accelerator is key, so follow the dose ratio in your instructions kit, which can differ based on the exact glue and accelerator in your kit.
Coat the seam and the patch with a thin layer of glue; it should look watery. Allow the glue to dry five minutes. As with the solvent, perform two more glue applications and wait five minutes in between each.
Wait for 10 minutes after the final glue application. At the end of 10 minutes, press the patch over the seam, pressing hard to remove all air bubbles.
Allow the glue to set up for two full days. Do not move your boat for 48 hours while the glue cures. The glue will continue to strengthen for seven days from the day you applied it.