I had some interest in my first boat upholstery project and some people wanted a step by step process so here is how I am doing mine. If you have any constructive critisism or good tips or how something should be done different it is welcome but if you have never done upholstery I don't want to hear how you think it should be done.
Before getting the boat seats out of your boat make some marks on the upholstery if you want to change some of the lines in the trim work so you will be able to make everything line up when finished. Then remove all pieces to be worked on. Then I drew on my exsisting back rest what I wanted to change with the different pattern.
The first thing I made was the piping for the bottom cushion. At first I pinned the pipping every 2" or so and then sewed it, but then learned by doing it free hand at 3" at a time saves a lot of time and is easy. With your zipper foot and needle to the side this was a very basic way to start getting used to sewing. Make sure the cord you buy is a marine foam type cord and is not the cotton kind. I am using a 4 oz. bonded nylon thread which I don't really know if it's good or not but thats what the lady at the place where I bought everything told me to use. I am also using a #16 needle and am stitching about 8 stitches per inch.
Next with a seam ripper or razor blade cut and rip all the seams that you want to take apart. Make sure to label everything how you want it to make it easier and not mess up with the wrong colors. For me DG=dark grey LG=light grey BL=blue obviously.
Next I lay my vinyl face down on my table and put my patterns face down on the vinyl and trace out all the patterns. On all sides that are not stapled to the seat base I allow 1/2" for the new sewed seam. All the old seams are folded over and if you unfold them it should line up with your pencil mark you just made or be a hair smaller. The factory seams are only about 1/4" and I am sewing everything at a 1/2" so take that extra 1/4" into account or you will have to really stretch your final skin over your seat.
Then sew all your patterns together to make your new skin. To get the most important seams lined up I start at that seam even if it is in the middle of a longer stitched seam. Like the blue stripe wrapping around the edge of the seat. When your skin is done snip all the curved seams about half what to the stitching so it will form around the curve nicer.
Put you skin on your padded seat base for a test and it should look a little small to cover you old foam seat base. For your piping seam there will be an extra piece of vinyl to conform around the foam and look like to different panels on the cushion. I draw to parallel line on this piece to see how I can keep the staples in the same place so my finished product looks even.
Then I finish stapling the skin to the back of the seat base and insert the front foam peace and staple the rest of the cushion. The staple gun I am using is a standard hand staple gun, not electric or knewmatic. In harder surfaces the staples are left up 1/32" and I just hit them in with a hammer.
Here is my finished product of the observers seat. I am very happy how it turned out and it is very simple once you get doing it but does take a lot of time and patients. This cusion and back rest took me approx. 6 hours start to finish.