Most people don't get motion sickness while driving a car or piloting a boat/plane; that's because you're directly effecting the action of the vessel, you see what actions you have to take to steer a clear passage, you anticipate and react to the dynamic forces that result from such actions. Your mind/body kinesthetics are synchronized and you don't get motion sickness, because you're mostly in control and can see the dynamic environment in front of you.
Now short of going up to the wheelhouse and actually taking control of the boat, try sitting with the Captain at the Wheel, let him talk to you about how he's steering the boat and actually see/anticipate the resultant boat motion in response to his actions.
In other words . . .don't anticipate being seasick --anticipate being in control, knowing & feeling what the boat's motion is going to be. With practice of this simple visualization, you can even "quell the queasiness" in the roughest sea conditions --all without any medication of any kind.