A Bulbous Bow (yachtforums.com)

What exactly does the bulbous bow do? The bubble breaks the friction between the ocean and the steel of the ship.  In return, the ship is more fuel efficient and cuts through the water more smoothly. 

What kind of material is it made of? The same type of material the hull of the ship is made of, steel. 

What kind of ships have a bulbous bows?  Passenger, container ships, car ships, military…. mostly any ship that draws more than 15 ft of water.

How long have they been around for? Most ships that were built in the 1980′s to current have these bubbles installed on them. The bubbles were used in early as the 1930s but were known as experimental.

You mentioned the bulbous bow is fuel efficient, how so?  Depending on the metrics of the ship it can reduce the drag through the water up to 15%. Less drag, less friction, less fuel usage.   

How deep does the bulbous bow go? The bubble goes down to the keel (bottom) of the ship.

Can a harbor tug hit the bulbous bow if it gets to close to it? Yes, and when it does, it will shake the whole ship …. steel touching steel is not good.

Could a tug hitting it compromise the integrity of the hull?  Of course, any outside force can. Look what a sheet of ice did to the titanic.