Mullins did offer various aluminum hulls in the 1920's.
However, they made a wonderful steel model called the Sea Eagle. Been on my watch list for years. Also known for their swoopy tow behind clamshell trailers from 1936. Those are reproduced in fiberglass for the street rod folks.
1952 Deluxe Runabout with 1956 Johnson 30hp 1959 Deluxe Clipper with 1973 Merc 500 50hp