These cockpit cushion instructions step through the process of making a boxed cushion for a boat using closed cell foam, a water-resistant material, with zippers and piping (welt). With a few exceptions, which I’ll point out, this “recipe” can also be adapted for interior cushions with softer foam and even with other types of cushions such as “waterfall”. So this is the basic cushion recipe and other, fancier cushions are just variations on this theme. And the only thing that makes these cushions different from those you might make for a patio or other non-boat location is that if you’re not on a boat you probably have the luxury of having rectangular cushions!
Plates are the top and bottom of the cushion, boxing is the sides that connect the top and bottom plates. Zipper boxing is the boxing that has a zipper in it – usually it will be the back size of the cushion plus 3″ on each side of the back for ease in getting the foam into the competed cushion. A zipper is composed of the zipper teeth and the zipper pull. A zipper placket is the material framing the zipper – usually each short end of the zipper to keep the pull from running off the teeth at either end, as well as the protective flaps that cover the teeth from view, although these are not strictly required if you wish to leave your zipper exposed. Piping or welt is the cloth-covered cording sewed into the seams of the cushions to prolong the life of the seams and provide visual interest. Technically piping is found in clothing and welt on furniture, but they are the same thing. For interior uses the cording inside the welt can be cotton or silk, and harder extruded foam or dacron leech line is often used for exterior purposes to avoid mold when the cushions get wet.
Choosing the materials for the cushions is an article all its own. Read about choosing cushion material choices, then come back to this article when you have your materials selected. For the cockpit cushions discussed below I selected closed cell foam, phifertex, YKK #10 zippers, and vinyl piping (pre-made).
Figuring Amounts and Making Patterns
Once you have chosen materials you can figure out how much material to buy. Using the example of cockpit cushions, first figure out how many cushions you will make. On the interior of a boat you might decide to make separate cushions for a settee rather than one large one, but generally in a sailboat cockpit you will want to make each cushion as large as you can and minimize the number of cushions.
First decide if you want to be able to swap cushions – if the port cushion is the same size as the starboard cushion you could double the life of the cushions by making them swappable – the cushion could go face up on one side or face down on the other. This would mean that the top and bottom should be the same material and that piping, if any, would be on top and bottom. It would also mean that you ignore minor differences between the cushion patterns and just make two exactly the same.
Measure all four (or more!) sides of each unique cushion. Use the material estimator app by Sailrite or draw it out on graph paper with the width of your material indicated.
I use a piece of visqueen and a sharpie pen to create a pattern at the same time I measure. I use the measured numbers for ordering the material but use the pattern for cutting out the material.
Once the materials arrive you are ready for the construction steps!
- Cut out foam. Closed cell foam should be the same size as the space or the pattern you made. (Note: Softer foam is cut 1/2″ larger than the space in each direction and the fabric is cut the same size as the foam.) Mark the pattern on BOTH sides of the foam so you can tell while cutting whether you are keeping the knife perpendicular to the surface along the cut line. Cut foam with an electric carving knife, checking both sides as you go. Cutting in front of a mirror might help with this – or just keep checking the back side as you cut. You may want to practice cutting on scraps if you haven’t tried this before.
- Cut fabric plates from foam. Lay the foam on the wrong side of the material, add a 1/4″ allowance on each side of the foam (Note: for soft foam add no allowance). This means that for a closed cell foam cushion 10×15 the plate will be cut to 10.5 x 15.5 – a quarter inch extra on every side. You will be sewing a 1/2″ seam on each side which will squish the foam just a bit for a more attractive fit. Mark “INSIDE, Top, Cushion #1” on the material. Repeat for second plate, remembering to flip the cushion and mark this plate as “INSIDE, Bottom, Cushion #1”.
- Cut zipper panels and boxing. Width: Boxing is measured the same way as plates – 1/4″ wider on each side than the thickness of the cushion for closed cell. This would be 2 1/2″ for a 2″ pad. Add another 5/8″ to the width of the zipper panel – 3 1/4″ for 2″ foam. Length: Zipper panels should be along the long, back side of a cushion, and wrap around each neighboring side by 3 inches or more. Foam is very contrary when you go to insert it in the cover, so wrapping the zipper around two of the back corners helps when inserting the foam. I like to cut my boxing in one piece, but if you have made it in shorter pieces combine them now to cover the three sides of the cushion not covered by the zipper panel.
- Make zipper panel. There are multiple ways to do this, my favorite is the standard zipper placket technique featured first in Sailrite’s Zipper 104 video . For this method you cut the zipper panel 5/8″ wider than the boxing strips. Fold the zipper panel in half the long way and sew a 1/2″ seam on the placket. Now CUT the seam exactly down the middle so that you end up with two pieces of fabric basted together.
Press the zipper placket open so you have the seam running down the middle of the fabric and the short-cut sides facing up.
Lay the zipper teeth along this seam and sew the zipper to the placket close to the teeth being sure to catch the short sides of the pressed-open seam. You may want to use seam-stick to keep it all lined up.
Cut open the seam exposing the teeth.
Put the zipper pull on the zipper making sure to place it so the pull is on the correct side. Don’t laugh, but I have done this backwards! And once you sew the second end down…. here comes the seam ripper!
- Attach zipper placket to boxing. Now sew one end of the boxing to one end of the zipper placket, right sides together. Sew carefully over the teeth – you may want to drive the machine manually when you are directly over the teeth to avoid a needle strike. Now you have one long strip of boxing with zipper attached.
- Sew piping to both plates.Review the Sailrite piping video starting at 2:45 if piping is new to you. Return to the plates and attach the piping to the plates. Start the end of the piping in the middle of the side of a plate – several inches down from the corner. Also leave an inch or two of piping loose to do the join later. Sew the piping to the right side of the plate. You may need to turn the wheel manually at the corners. I usually get right up on the corner, turn the fabric 45 degrees, take one stitch, and finish turning the corner, then take the second stitch and proceed straight from there.
As you approach the beginning of the piping on the last side, stop and cut off more than enough to finish. Peal the fabric back from the piping core and trim only the core so it exactly meets the beginning of the piping. Wrap the excess piping fabric around the join of the two cores. Finish sewing the piping over the join and down to where you started. Repeat for bottom plate if you are piping both sides of the cushions.
- Sew boxing to one plate. Start with the zipper panel end of the boxing strip. Pin or staple or seamstick the right side of the zipper placket and boxing to the right side of the plate and piping. Make sure the zipper starts a few inches before the long back side and wraps around a few inches past the back side. Sew these together. When you get to the far end sew the boxing to the zipper panel end to complete the zipper placket. Now the boxing is in a rectangle with one long edge attached to the plate.
- Sew other plate to boxing. Before sewing mark the corners of the boxing where it will attach to the new plate. For large cushions you may want to mark additional places where the boxing and plate should match up – or you may just seamstick, pin, or staple the two pieces all the way around, right sides together. Once you have it lined up to your liking, sew the plate and the boxing together. Turn the cushion cover right side out.
- Insert foam. This can be the most exasperating step, particularly with stiff closed-cell foam. Slightly rounding the corners with your electric carving knife can ease the corners a bit, especially near the zipper. Wrapping slippery material around the foam – such as silk, nylon, or plastic wrap – inserting the foam and withdrawing the slippery layer can help. Or just keep pushing, inch by inch and it will go in. Gently cursing seems to help. And remember – the more difficult it is to insert, the more crisp the edges of the final product will be!