Ok, here we go, a subject close to my head & tummy! :-D
I find I have less of a tendency to get sick on the six-packs than I do on a cabin cruiser...probably just me. The cabin cruisers, although are heavier and don't toss as much, they do ROLL quite a bit, and that is what does it for me more than rough seas...gentle rolls! yikes!
Also, usually when I'm on the larger boats, the diesel exhaust seems more prominent, and contributes to me getting sick.
I take 2 Dramamine tablets for motion sickness. I used to take only one, but it only worked occasionally. After reading the directions, I realized a dosage of 2 could be taken. Directions! Who wouldda thunk it!?
DAN's Diver Alert magazine also suggest taking Sudafed and/or Benadryl. I take Sudafed & sometimes a Benadryl as well. Especially if I've been into the Hydroids!!
Seems like a lot, but I've been doing this routine for the past couple years, and it seems to be working.
I only got a little sick after the second dive, once this year over 2 weeks diving (my first day of boat diving, when I was on a cabin cruiser, by the way).
Last year I actually made it until the last day of diving before I got sick ( again 2 weeks of diving morning dives), and I think that it was more to an ear issue than true sea sickness.
Also try to have as full a stomach as possible. An empty stomach or one with just fluids sloshing around can contribute to getting sick. I usually also take a breakfast bar or some crackers onboard, just in case the SI fruit and muffins aren't quite enough, or if I should need something on the way out or before the snacks get broke out.
Oh, hydrate, hydrate, hydrate...see above...and then hydrate.
I also have heard that ginger helps, I tried to find ginger snaps at Mega this past trip to no avail.
Unfortunately, from all the people, like us, that I've talked to, no matter what precautions you take, sometimes it just happens. So do everything you can to prevent it, and go out and have a good time.
We usually go in the Spring (late April - late May), the seas are USUALLY very calm in the mornings, getting somewhat choppy occasionally with the afternoon winds, and then flattening out in the late afternoon.