You mentioned sail-training boats in your post and I wondered what kind they are? How long have you been sailing? Most trainers and even the large boats in decent swells will prepare you stomach for anything you can imagine. Much better than roller coasters any day! We took out a 61ft sailboat in the Aegean and had some pretty good swells with it and I thought I was going to be miserable from sea sickness, have my IBS act up or both. Fortunately I did great while six others on our crew weren't doing so well. Maybe IBS and sailing go well together.