We have seasickness tablets on board for those that need them, and also stop regularly in the day. Sea sickness is very rare on our trips because we cruise carefully, and reschedule if we think the weather is unsuitable. The waters in the bay are more sheltered than around Phi Phi. So if you are worried about sea sickness, particularly in the period May to October, a trip of the bay may be a better option than a trip to Phi Phi.