A man found guilty of murdering his three sons by driving them into a dam in south-west Victoria has been sentenced to life in prison with a non-parole period of 33 years.

Robert Farquharson was found guilty of deliberately killing his three boys, Jai, Tyler and Bailey in July.

They drowned when they were trapped in their car at the bottom of the dam near Winchelsea on Father's Day in 2005.

During the hearing, the boys' mother, Cindy Gambino fought back tears.

Outside the court she told reporters the sentence was never going to be enough.

"I have a life sentence, so should he," she said.

Farquharson, 41, shook his head as Justice Lex Lasry told him he had planned a horrendous crime and delibrately killed his vulnerable children.

Justice Lasry told the court the boys were subjected to a terrfiying death, which had traumatised their mother for life.

Solicitor Simon Northeast said Farquharson is innocent.

"In due course we will be lodging an appeal," he said.

Ann Irwin read a statement on behalf of Robert Farquharson's family, friends and supporters outside the court.

She says they maintain he is innocent.

"We as his family and supporters are not so blinded by love or sympathy that we would maintain his innocence if there was any evidence of guilt," she said.

"Rob is a broken man, a traumatised and deeply grieving parent who loves his children. He finds it difficult to accept the deaths of his boys and will carry this grief with him forever."

Ms Irwin says those who have not experienced what he has cannot judge him.

"Despite the fact that it is hard to accept, this was an accident. We are both devastated and outraged at the verdict," she said.

"The justice system has failed three young boys and their loving father and we are horrified that Rob is now faced with further trauma, grief and loss of liberty as a result."

Farquharson will be in his 70s before he is eligible for parole.

The sentence was delayed by about 90 minutes because the boys' mother, Cindy Gambino, was unable to make it to court on time because of bad weather.