Kwells (hycosine) is considered more effective than Bonine (meclizine), but is also more sedating.Since this thread popped back up - last couple dive boats I've been on, both in Maui, Bonine has failed me. Works great for air travel, works great on cruises, but if it's really bumpy out on a small dive boat...the Bonine might stop me from throwing up, but I still feel absolutely terrible and I'm exhausted by the time I get back to the dock. Last week I was in the Keys and went out and tried Kwells - I'd bought some last year at Heathrow. On the 45 minute boat ride out to the Spiegel Grove, on the 45 minute surface interval, and on the trip back, the Kwells managed the nausea much better than Bonine had. Maybe the smallest hint of some discomfort but nothing near as bad as I'd felt on similar trips with Bonine.
Sedating is usually discouraged if you are diving.