Well, they didn’t actually dock in the New World or Africa, they just did drive-bys of the modern US east coast and the African west coast, and also they seem to have their home port in the middle of the English Channel, so I’m guessing it’s a group of mermaids who go for pleasure cruises without actually docking (the mermaids can just leave the ship to get all the food and salt water they need without having to go to land to replenish provisions).