<em>The average density of the boat, including the steel and air, is less dense than 1.00 g/cm³. ... lake water is more dense than pure water. steel has a special ability to float regardless of density.</em>
The shape of boat allows the boat to have an average density less than one and also causes displacement of water in large amount.
Explanation:
The floating of an object is governed by Archimedes principle which states that the amount of water displaced by an object when it is placed in water must be large enough to allow the object to float.
When the steel metal is carved into a boat, its shape and surface area changes due to which it displaces a larger volume of water thereby causing the boat to float. Also the average density of boat as compared to its surrounding water gets lesser than unit g/cm^3 which also causes floating of steel boat in lake water.
