Boat trailers are available in different types of materials.  There are pros and cons to each of them.  Here are some of the differences:

Aluminum boat trailers: Aluminum is a light weight, but very strong material.  some of the advantages are blah blah blah

Galvanize boat trailers: Galvanized trailers are made of steel that has been has been hot dipped in a liquid zinc bath for corrosion resistance.  Very durable trailers blah blah blah