Lawyer John May said his client, Leslie Alan Gardner, 62, of Gillette, was suffering from delusions when he stole the yacht from a Sausalito harbor in March and crashed it on a Pacifica beach, the San Mateo County (Calif.) Times reported Friday.
"He truly believed it was his boat," May said. "I'm trying to get him appropriate mental health help."
Gardner was deemed mentally competent to stand trial Thursday.
May said his client served in the U.S. Marines and fought in Vietnam from 1968-70. He was discharged with post-traumatic stress disorder, May said.
Authorities said a couple joining Gardner on the yacht trip told investigators they believed the yacht belonged to him. They were released without charges.
Gardner is in jail in lieu of $1.01 million bail.