There are deck walls strong enough to prevent a vehicle falling out of the ship, but usually open at either end to ensure good ventilation. There are hundreds

There are deck walls strong enough to prevent a vehicle falling out of the ship, but usually open at either end to ensure good ventilation. There are hundreds of these ferries operating in Europe (and other places with large islands or short seas/lakes), from tiny ones that carry 2-4 cars, to large ones with multiple decks. https://www.alamy.com/stock-photo/car-ferry.html?sortBy=relevant https://www.alamy.com/stock-photo/car-ferry.html?sortBy=rele... Tiny (UK): https://www.alamy.com/the-dartmouth-to-kingswear-car-ferry-leaves-from-bayards-cove-dartmouth-image150265426.html https://www.alamy.com/the-dartmouth-to-kingswear-car-ferry-l... Small (Germany): https://www.alamy.com/stock-photo-car-ferry-harbour-friedrichshafen-lake-of-constance-baden-wurttemberg-147274580.html https://www.alamy.com/stock-photo-car-ferry-harbour-friedric... Medium (Brazil): https://www.alamy.com/stock-photo-car-on-board-the-ferry-makes-the-crossing-between-the-city-and-the-101304128.html https://www.alamy.com/stock-photo-car-on-board-the-ferry-mak... Large (UK/France): https://www.alamy.com/stock-photo-the-vehicle-deck-of-a-cross-channel-car-ferry-on-the-dover-calais-73449924.html https://www.alamy.com/stock-photo-the-vehicle-deck-of-a-cros... Note these are public passenger ferries. You arrive at the port, buy a ticket, drive on and (usually) get out of the car for the journey.