Semi-submarine

A semi-submarine (semi-sub) is a surface vessel that is not capable of diving, but has accommodation space below the waterline featuring underwater windows.

Both types of boats are mainly used to provide sight-seeing trips for tourists in clear, calm, and often shallow, waters.

The cabin is equipped with large underwater windows, so the passengers can observe the marine environment that is passed during the voyage.

As the hydrostatic pressure close to the water surface is relatively low, the viewing windows can be large.

Since the semi-sub interior is always open to the atmosphere, no special measures must be taken to assure a supply of breathable air to its occupants.