The 67-year-old star said he missed his friend who wrote What’s Another Year, the first of his three Eurovision wins in 1980.
"I loved Shay. Everyone that knew Shay loved Shay,” said Logan.
"Shay was funny and incredibly bright. He faced his Parkinson's with great courage.
"Everything that has been said about him is true - and it's not enough.
“Shay was the kind of friend who was there when it was bad and good. I didn't always agree with Shay - many times I wanted to choke him and he probably felt the same for me.
“But I loved him, I love his children Fionain and Oisin and young Finn his grandchild.
“My life is less bright for Shay not being in it. I miss him. I miss him still.”
The star was speaking on the first episode of Soundtrack To My Life hosted by Niall “Bressie” Breslin which will be broadcast on RTE One tomorrow night.
The singer performs a variety of songs – including Gone, Gone, Gone by Led Zeppelin’s Robert Plant – in the music and chat show, accompanied by the RTE Orchestra.
He will be joined by singers Luka Bloom, Jerry Fish, Grainne Duffy and Jimmy Smyth.
“When you hear What’s Another Year and Hold Me Now it's hard to believe I was a huge Led Zeppelin fan when I was 16,” says Logan.
“They were playing in the National Stadium in Dublin and there was a bus strike so I walked from Drogheda to Dublin and saw them in the stadium. I slept in a doorway and walked back the next day.”
The star, who won the Eurovision again in 1987 with Hold Me Now and wrote Linda Martin’s winning song Why Me? in 1992, said he was staggered after his second win because he had also written the song and felt under huge pressure.
“I was representing Ireland again. I had already won it with What's Another Year so second place wasn't good enough. I had to win again.
“The levels of pressure on me were unreal. I remember after I won I went into the bathroom and ended up bawling my eyes out for about an hour.
“It just all kind of flowed out of me. People see you on stage and they see that three-minutes and think, ‘he's done a great job.’
“They don't realise it's really like looking at a duck on water. What you are seeing on top is someone in control but what is going on underneath is, ‘God, God, help me!’”
The singer revealed there were times he wanted to quit the music industry but the love of his fans kept him going.
“I love the contact with the audience. What has saved my life and saved my career on more than one occasion has been my fans and the people who enjoy my music.
“They have brought me to this place where now I have my own publishing company, my own record label, I record what I want to record and I write my own songs.
“It was not always like that. Back in the 80s the major labels would hoist all the music from their publishing companies onto the singer.
“Even after Hold Me Now nobody wanted my songs, my writing. They wanted me to record other people’s stuff all the time. You think they know better than you do but the reality is they don't.
“Fans saved me because they showed me people still believed in me.”
He said he made an album in Denmark in 2001 where that year’s Eurovision was being held and he was a guest on the National Song Contest.
“I sang What’s Another Year and Hold Me Now and got a standing ovation that you would not believe.
“I put my heart and soul into it and at that stage I wasn't sure I wanted to stay in the music business. The reality is I had just lost heart.
“And the Danish audience actually stood up and gave me a standing ovation which went on for about five minutes.
“I remember walking off that stage and thinking, ‘Yeah, that was worth it. I have got to get that again.’
“It just made me believe in me again and over the years that has happened again and again.
“There are still these moments when you sing a song and you get lost in it and the audience gets lost with you. I'd rather have that than the money you can make out of the music business.”
Soundtrack To My Life is on RTE One on Saturday night at 9.50pm.