Worry about seasickness keeps some people from saying yes to a ceremony at sea. It is a fair concern. The good news is that a few simple steps help many people, and most of them start before you leave the dock.
Off San Diego, mornings are often calmer than afternoons, when the wind tends to build. If someone in your family is prone to motion sickness, mention it when you plan the date and time. See how to choose the time of day and wind and sea conditions by season.
Some motion sickness medicines are sold over the counter and others need a prescription. According to the CDC, they work best when taken before the trip rather than after symptoms start, and drowsiness is a common side effect. The CDC also warns that scopolamine, including patches, should be avoided in children. Ask your doctor or pharmacist which option fits you, especially for children, during pregnancy, or if you take other medicines. Acupressure wristbands are popular, but the evidence is mixed; the CDC describes studies finding them no more effective than a placebo. Some people still find them comforting. The CDC's Yellow Book page on motion sickness has more detail.
This is general information, not medical advice. Your doctor or pharmacist knows your health and can tell you what is safe for you.
For layers that keep you warm on deck, see what to wear on ceremony day. If you are unsure whether a ceremony at sea is right for someone, call (619) 986-7344 and talk it through. There is time to decide.