To make the stack pack, I used:
- 3m acrylic canvas (non coated)
- 1 reel of venture tape (double sided tape for sticking before sewing)
- 1m webbing to attach sail slides
- 6x sail slides
- 80cm zip
- 3m zip
- 1 cone of thread (uv resistant)
- 2x 3m x 8mm Fibreglass rods
- Sewing machine (most domestic ones will do)
- Denim needles for machine, 100/16 denim reinforced ones
- Tailors chalk for marking
- Sharp scissors
- Sharp craft knife/stanley knife/scalpel for cutting out shapes
To begin, measure the length of your boom. This will be the cover length. Next measure the circumference of the flaked sail at 50cm gaps along its length. Although technically we'll only use the two end measurements its a handy cross check to make sure everything will fit. As I always say, measure twice, cut once!
When measuring the mast end, remember that when the sail is in the mast groove it is significantly higher than the rest of the sail.
Don't measure this part since it will have a separate cover and will make the main bag too large. Instead, measure without the sail in the mast groove, this can easily be done at home.
Now we have the measurements for the cloth cut it's time for a model. Use 10:1 scale so 1cm is 1m to keep it simple. For mine this allowed me to use a4 paper but a3 will work for most sizes. The main bag body will be two halves, cut in opposite directions to reduce wastage. This means we end up cutting a rectangle then halving it on a diagonal. First, fold your paper in half length wise. Now all measurements from this centre line will be half of the circumference required. For the closure on top, you'll want a slightly wider gap at one end than the other, I used 10cm at the stern and 15cm at the mast, this is not a set figure, just use what looks right on your sail and boom. For larger boats make them a little bigger.
Divide your sail circumference by 2 at each end. Divide your top closure sizes by 2 at each end. Subtract the half top closure numbers from their respective circumference numbers. This new number is the bottom half of the bag. On your paper, mark the boom length along your middle crease, adding 5cm (5mm at scale) for a seam at each end. Next, mark 2mm out at each end of the boom length for seam width. Now mark the figures you just worked out at each end and join these up to show the shape of the bottom half fabric. At this point is where the rods will go so we need to mark some extra space for the tubes. This will be Pi x the rod thickness plus some slack. For my 8mm rods I used 4cm. Mark this distance out at each end and join these with a line. Next, mark the top cover sizes out from these and join with a line. Finally add 2mm for another seam and join with lines.
At this point you should have a centre line then lines for seam, bottom, rod and cover at various distances out to form a sort of triangular shape. Remember when marking on the fabric you can measure these distances back to check them. Transfer the lines to one side of the fabric role for half of the shape. The other half should be marked in the opposite direction.
Using the venture tape, fold the 5cm seams in at each end and stick down. Sew a line close to the fold and one close to the fabric end. Next, cut holes for the lazy lines. These will be 2 or 3 holes at sensible gaps along the length. They should be biased toward the mast since this is where most of the sail cloth will come down.
Cut a rectangle hole the width of the rod tube markings and 5-6 cm in length. Reinforce the sides by sticking rectangles of fabric and sewing in place.
Next, tape and sew the zip into place. To do this, tape the outside of the zip to the outside of the bag. When you sew it and pull it back it will then look very neat. Sew one side of the zip at a time with the zip separated, halfway you'll need to move the zipper along otherwise it gets in the way, just lift the sewing machine foot briefly to do this.
Finally the bottom of the bag. My sail has slides so I aligned these with the bag and made more reinforced holes. Halfway between these I sewed webbing with slides into the seams to attach the bag. My sail now attaches through the holes in the bag. For sails with bolt ropes, you may need to add a section of thin cloth such as nylon which then slides into the boom with the sail rope.
For the mast bag, I measured the circumference of the sail about 50cm back from the mast and the height with the sail in the mast. I then drew a curved shape to accomodate this sail and cut the two halves. At the front of the bag I allows sufficient fabric to wrap around the mast and add a zipper at the front.
Hope this helps someone, please leave a comment if you have any questions.