Ok, from growing up on the ocean and on boats I to know a bit about this subject. I don't get seasick easily, however I do have memories of being curled up in the fetal position in the rear cockpit of our 55' Hatteras with one arm hooked through the ladder to the flybridge and breathing diesel fumes. I also remember mustering up the energy to crawl to the head in the v-berth, sticking my head in the lav, dry heaving, and saying out load (with honest conviction) "Please God, .....Take Me Now"!!!
Fundamentally, the objective is to keep the stomach from experiencing changes in gravity caused by the forced rising and falling caused by the sea's waves! Here are a few bullet points that are very simple to follow:
1. Be careful of what and how much is eaten before a boat ride. Eating four eggs, bacon, sausage, toast and a glass of milk at 7:00am before a 8:00am boat ride is a recipe for making vomit. It is the weight of this food setting in one's stomach and bouncing up and down with waves that give the body the urge to toss it's breakfast. Eat very, very light non-greasy food (or not at all) a few hours before the ride.
2. Try to use the largest boat available. Going out in rough seas in a 4 meter rib isn't a good idea unless you really need a diving fix.
3. When on the boat stay toward the stern. The front of the boat is the apex point that experiences the most rise and fall. Stay near the fulcrum point that has the least amount of rise and fall.
4. Stay away from exhaust fumes. Small runabouts aften outrun the exhaust fumes, so being positioned at the stern is smart, however larger slower boats such as a 55" sportfish with a flybridge create a backwash effect and will suck the fumes into the rear cockpit area. Find just the right place to stand a little ways forward, keep your face forward and toward the the oncoming fresh air.
5. Let you legs function like shock absorbers. If the boat is big enough, try not to sit. Stand with the knees slightly bent and try to keep your torso from experiencing as much rise and fall as possible.
6. Watch the horizon. This is the ultimate gauge for trying to minimize the torso from going up and down. Staring out at the horizon, with the legs functioning as shock asorbers is one of the best things one can do.
7. Prescription motion sickness meds. I forget the name of it, but a friend of mine has a prescription for a medication that works great for preventing sea sickness. I have taken it a few times and it works even in rough seas. One side effect is it causes dry mouth, so while diving on scuba, my mouth and throat became horribly parched.
............just my two cents,
Jim