These Shin swim shorts were a labor of love -- comixminx made several test pairs in stretchy fabric to refine the fit. She shared lots of tips on Discord along the way. A couple key ones:
A microtex needle worked very well on these fabrics
As drafted for the recipient's measurements, the crotch was too angular; smoothing out that seam made it more comfortable
A fake coverlock stitch looked great from the outside, but may have reduced comfort -- make sure you think about the wearer's comfort for each seam of this pattern