Besides the good information that Raoul gave you, I think you should consider the following.
Many people think about getting seasick. The best advice we can give you is to ask your family doctor for a prescription for [Transderm-SC 1.5mg Dis Nova]. This is a medicine which prevents nausea and vomiting associated with motion sickness. It is a small patch that you place behind your ear. The patch is good for three days, then you must replace it. It will stay on even when you shower. You place the patch behind one ear, the morning of the sailing!!! This gives the medication a chance to start working. Also when you have to change the patch, do it first thing in the morning. It definitely works.
Tom & Mary