I drafted and made my second sports top prototype yesterday! It isn't quite finished - I decided to edge the arm and neck openings with fold-over elastic, and of course don't have enough in my stash. So this will have to wait until Monday.
I drafted a pattern based on the Rooie Hempje basic pattern (adjusted for bust apex height and side seams shaped based on my muslin), following the instructions for a racerback top with minor modifications.
Before cutting out, I considered the stretch of the heavyweight powernet I was planning to use - it has 80% stretch with excellent recovery. I measured my old sports bra and it was 76 cm (30") around - 4 cm (just under 2") smaller than my underbust measurement (and this is a TIRED top). I then measured the pattern, which was 100 cm (39") around the bust (5 cm, 2" less than my bust measurement), so I reduced the pattern at center front (4.5 cm, 2") and center back (2.5 cm, 1"), reducing it by a total of 14 cm (6"). After sewing it together, I took away another 5 cm (2") in the side seams.
I didn't have enough fabric to cut out the back in one piece, so I divided it along the dart line from waist to armscye.
I cut the front with a centre front seam, also because of the size of my fabric.
I am quite pleased with the results. It feels comfortable, though producing a uniboob effect. It actually provides some lift in front and fits very well in the back. I think my racerback adaptation needs some fine-tuning - I was scared of making the straps too narrow, but I think they would benefit from some paring down, especially next to my neck.
This is what it looked like after the further adjustment. (You can see what a great job the powernet does with compressing my waist - a reverse muffin top.) I think I will also make a separate pattern for left and right - it is obvious here that I need more fabric on the right-hand side armscye.
Next, I did some gathering in the front and it does help with the uniboob a little. I also did a little experimental princess seam from the bust apex to the armscye. I am thinking of taking the centre front seam apart and introducing a dart there or otherwise gathering and then sewing together again.
I added 1"-wide plush elastic to the bottom in the usual lingerie way. I have been wearing it for a few hours now and will start a Pilates trial as soon as I've finished this post. Here I am this morning with a strappy top over the bra (am planning to make a matching racerback top in black cotton lycra - maybe even today!)