Re: Cockpit side rail cushion??
Those pads are called
coaming pads. Obviously, they are there for you to lean against when fishing. They are simple to make (I am an upholsterer).
Measure out the length x width that you need and scribe it out onto a 3/8" piece of laminated plywood (I recommend StarBoard). Be mindful, it might be better to make a template out of paper because if the pad is that long, it will rarely be a straight edge on the top of it. When the hull curves outward, it causes the pad to have a slight arch to the top.
If you don't want any cool designs or varied dimensions, it will be all the easier for you. Line the board with 2" soft foam (available at any discount fabric store or Wal-Mart, K-Mart, etc) and lightly glue in place.
Cover with the fabric/vinyl of your choice. You can get the cheap stuff from the same stores, but it looks cheap. Spend a little more and you'll be happier with the end result.
S-t-r-e-t-c-h the material around and staple to the back side. You have to put a little effort to stretch the vinyl, because you want it to compress the foam a bit (leave it about 2/3 the original thickness). When you get to the corners, you can go amateur and make a fold, or if you have a heat gun (hair dryer in a pinch), heat it carefully and you can work it around the corners without folds. Sight down the long axis of the board and make sure that the foam looks evenly compressed down it's length. Having it wavy makes an otherwise decent job look sloppy.
To really trim it out, it should have a welting cord on the backside of the pad, to take up any space between the back of the cushion and the hull itself. They are rarely perfectly flat. If you want that, take your material to an upholstery shop and they can sew it up for you very inexpensively (and give you tips if you ask).
Trim off any excess and mount it to the boat. If there are previous holes where the old one was bolted in, you'll have to sink in t-nuts to the board prior to upholstering. For 3 pads, allow yourself about 4-6 hours.
