Complex sentence: Huckins also granted permission for Elco, Higgins and the Philadelphia Navy Yard to use their patented laminated keel, which increased hull strength, although neither Elco nor Higgins ever chose to use the Huckins design on their boats; they instead used designs of their own.
Split into simpler sentences: Huckins also granted permission for Elco, Higgins and the Philadelphia Navy Yard to use their patented laminated keel, which increased hull strength. Although neither Elco nor Higgins ever chose to use the Huckins design on their boats, rather choosing to use designs of their own.