Hi Alicia! Your's is an excellent question regarding using ginger products for preventing motion sickness.
From what I have read, the proper dose to of ginger tablets or capsules to use in the prevention of motion sickness is two tablets or capsules three times a day (so with each meal would make some sense). You should start taking them about two days before boarding the ship, and continue through the end of your cruise.
Be forewarned that some people have complained about the ginger aftertaste when using these products. Every little burp may bring another little surge of "flavor" to your mouth. Chewing a cinnamon flavored gum or sucking on some mints may be helpful if this is a problem.
Does this answer your question, Alicia? Let me know if you want to know more about ginger treament. I'll see what I can find.
Have a great cruise!
John Burns, R.Ph.