Why do I bring this up? Fiberglass boat hulls may be one peice and the entire walking surface inside of the boat may be one other peice. Manufacturers may make an entire boat frame out of 2 parts if fiberglass is used, while steel or aluminum or wood would take thousands. This alone makes fiberglass ideal for the production line.
Now, it is important to note that fiberglass will not necessarily be stronger than steel or aluminum when used for this purpose. Fiberglass has more ability to bend than either steel or aluminum, and it will bounce back to its previous shape. However, at higher impact levels, fiberglass may be shattered while steel and aluminum are simply bent and may be hammered back into position.
As a result of these factors, the smaller the boat that is to be produced, the more likely fiberglass will be the best material suited to it.
Individually, a weight of fiberglass is stronger than an equal weight of steel. All the windows in your home, if processed correctly, could be combined to make a variety of fiberglass objects. Many stronger than most metals.