A removable fin assembly with at least one suction cup for attaching to a small watercraft and a method for attaching a fin assembly using at least one suction cup to a small watercraft. The fin assembly removably attaches to the underside of a small watercraft with the fin extending downwardly. The fin assembly is made up of at least one suction cup, at least one distributor to spread out the forces across the suction cup or cups, and at least one fin. The fin can be a traditional fin, a hydrofoil keel, or something similar. An optional shell can be added around the attachment location to reduce drag. Recesses can be added to the distributor to help support the fin or reduce drag.