Is it safe to go on a boat while pregnant?

Yes. Boats are safe if you take precautions. Be sure to wear a life preserver while you are the boat and stay safe. You may have more motion sickness while pregnant but it is okay to take dramamine (dimenhydrinate) or use an accupressure band for the nausea.
Yes. The same precautions apply to boats as they do to riding in a car. Instead of wearing a seat belt, I would wear a life preserver. Knowing the captain and how he or she behaves is like knowing who is driving the car or van.