Boston University professor of mechanical engineering William Carey, 69, who died Wednesday after a long illness, was known as a great friend, leader and award-winning scientist, colleagues said.

“Bill Carey was my friend and mentor,” said Ronald Roy, chair of the School of Engineering mechanical engineering department, in an email. “He had a totally unique personality—a real character.”

Carey, who joined the College of Engineering faculty in 1999, specialized in underwater acoustics.

Allan Pierce, ENG professor emeritus and close friend of Carey’s, said in an email that Carey’s knowledge was unparalleled.

“He very quickly emerged as the one person who knew the most at Boston University about the scientific and technological aspects of energy conversion,” Pierce said.

Pierce said he was department chair of Aerospace and Mechanical Engineering at BU from 1993 through 1999 and instigated Carey’s recruitment to the faculty.

He said he got to know Carey “extremely well” after he joined the BU faculty. Pierce referred to Carey as his “best friend.”

“He was also the leading person at Boston University in the general area of underwater acoustics (SONAR and other applications),” he said.

Carey won a number of awards for his work and research in underwater acoustics, Roy said.

“He was instrumental in the development of key acoustic sensing technologies such as towed acoustic arrays and low-frequency sonar systems for use in shallow-water environments,” Roy said.

Over his lifetime, Carey was honored with more than 20 awards for his work, such as the ASA Silver Medal for the Pioneers of Underwater Acoustics, the Distinguished Service Awards for the IEEE/OES and the Millennium Award from the IEEE/OES, according to a Curriculum Vitae provided by Roy.

“His breadth of knowledge in both fundamental and applied oceanic acoustics was virtually unmatched in the community,” Roy said.

Carey taught senior-level courses on energy conservation, Pierce said.

“I can’t imagine anyone who knew more about the subject at BU and who could have done a better job,” Pierce said.

Pierce said that although he spoke to him frequently before his passing, he did not expect him to pass away when he did.

“We were both in the process of retiring from Boston University, and I was looking forward to writing many more papers with him and also to coauthoring a couple of books with him,” Pierce said.

Preston Wilson, associate professor of mechanical engineering at the University of Texas at Austin and former PhD student of Carey’s, said he was grateful to have had the opportunity to learn from Carey.

“I am forever in debt to Bill for all the things I learned from him,” he said in an email. “In addition, his mentoring and support after graduation was exceptional. He was always looking out for me and his other students, helping us with our work and with our careers. He had so much to give.”

Roy said Carey always made time for his colleagues.

“I would often wander into his office looking for five minutes of advice and leave 60 minutes later having spent 55 minutes chatting about topics ranging from Celtic stone circles to Middle Eastern politics,” Roy said. “Of course, I also got my 5 minutes, and they were invariably golden.”

A memorial service will take place on Sunday, July 22 at 1 p.m. at All Souls Unitarian Universalist Congregation Church, 19 Jay St., New London, Conn. Donations may be made in his memory to Amnesty International, 5 Penn Plaza, New York, NY 10001, and condolences may be addressed to his wife, Susanne Colten-Carey.