Torn boat seat upholstery can cause extreme damage to the seat itself if it's not fixed. It's much more affordable to repair a tear than it is to replace the entire seat. Since most marine upholstery is made of vinyl, the repair is simple.
Step 1 - Prepare the Area
The vinyl repair kit should come with several components. You should have vinyl repair sheets, graining sheets, and directions. Heat the iron according to the directions provided. This is generally a medium setting so not to melt the vinyl. Pull the ends of the tear together getting them as close as you can.
Step 2 - Use the Repair Sheets
Place the vinyl repair sheet on top of the tear until it sticks together. Put the graining sheet on top of this and place the iron on the graining sheet for a few seconds. Most vinyl repair kits will suggest no longer than 1 minute, but larger tears may require more time. Allow the material to cool completely, and check to ensure the entire tear was covered.
Step 3 - Cover the Seat
It's a good idea to use a seat cover on any boat seat to protect it from tearing. These are inexpensive and can be found at any marine supply store.