Private yacht charters are vastly different from any hotel, resort, cruise or home rental you have otherwise vacationed. Life is simple and room on yachts is limited. Minimize packing to only the necessities, pack smart.
Seasickness is not as common on catamarans as monhulls. However, if sailing in rough sea or for a long period of time, away from the shoreline, seasickness may set in. It is a good idea to prevent seasickness with non-drowsy medication, to fully enjoy your trip.