MotionEase? Is that the herbal stuff you put behind your ear?
I ask because, pun intended, seasickness is all in your head. If I wanted a real cure I'd have to have my inner ears surgically removed. In the meantime, you need to try two things: Drugs, and getting used to it.
Cars, boats, planes, all the same, babies and puppies routinely puke the first few times until the get used to the motions. I still can't read in a car for any length of time and that's about true belowdecks on a boat as well.
But every time you go for a ride (in the car or boat) your system gets de- sensitized a bit and most folks quickly get used to it. It helps if you have had a good night's sleep, no booze no smoking (or smoke around you) for 24 hours, no real greasy foods onboard or right before, and if you keep your eyes on the horizon as a reference point. Fresh air, not being dehydrated, and not being excessively hot also help.
Then there's drugs. If MotionEase is that herbal stuff ot put behind your ear...good luck but I think you're wasting your money, I know I did. Their shipping charges guarantee them a profit regardless of the refund for the product itself--and yes I sent mine back. It only attracts bugs and bees, didn't help me at all.
Relief bands (that press the ne-kwan accupressure point) or the electric releif band (very good) work nicely. Also taking ginger (buy the supermarket spice and 100 empty capsules from your pharmacy, it's much cheaper than buying them pre-made) or food with lots of ginger in it helps. Ginger opens up the capillaries, that increases oxygenation in the body and brain, and that's a real help for as many people as ay other meds are.
Bonine, Meclazine, and other otc drugs all help some people, and don't help others. You may want to buy two or three and try them (on separate days) on land, to see if any make you sleepy or fuzzy-headed. There's no one magic answer, you need to try several to see what works for you.
On stronger drugs, there's sturgeron (otc in the UK, not available in the US) and scopalamine (patches and pills) by Rx only in the US. And a number of other drugs, all by Rx. The good news is, even if you need somethign the first time out, after a couple of trips your body gets used to it and you can wean off the drugs. Or, find drugs that work for you.
And in the worst case...You can take up motorcross instead. There's no one easy or complete answer, take charge, and do what works for you.