How do I overcome seasickness on boat dives without medication?

[gert7to3]

My mother administered cola syrup for upset stomachs when I was little. I have on occasion swizzled Coke to remove the carbonation and drank that to calm a sensitive stomach. I think the sugar and caffeine might help as well. I also seem to feel as though my body synchronizes with the boat's motion. Works fine on standard hulls, but a trimaran where the rhythm gets a third irregular motion defeated me once.