Why are Ships (Boats) made out of Steel?

[Coldwin]

What is the reason that ships are made out of steel. I know that steel is an alloy of Iron. What I need to know is why they don't sink and why they are chosen to make ships rather than other metals? I need your sources as well.

 

[RichardD]

Because it is cheap and strong. It is not the weight of the steel but all the water which it displaces which makes it float. Aluminum would make a lighter boat but it is not necessary in an ocean going vessel.

 

[fuzzy]

steel is cheap, easy to work & has known good properties. A ship floats because of the volume of air inside the hull. A hull will sink into the water until it displaces a volume of water (in liters) equal to the ship's weight in kilograms.
source : Google Archimedes

 

[CapteJohn]

Here is an easy to understand source (with graphics) of "Why heavy boats don't sink":
http://www.boatsafe.com/kids/021598kidsques.htm
Once you read the first paragraph on the link above - you will understand it really doesn't make any difference what a vessel is made of vs why it floats.
Large ships are made of steel mainly because steel is such a versatile construction material. It is strong, and can be easily cut, shaped, bent, wielded, and worked with.
Steel is really 'not' cheap. - it is in fact very expensive. . . It only becomes "inexpensive" when you consider what it saves in labor and other related costs when compared to using other materials. Pound for pound (for example) fiberglass would be cheaper, but your labor would be tremendously greater - which makes steel the much cheaper alternative for ship building.