A man was sentenced in the Palmerston North District Court on Friday to 18 years behind bars for raping, beating and tormenting his son. (File photo)

A son who was raped, beaten and tormented by his father will never have children, and says it's better the bloodline isn't continued.

The torment started with indecent assaults in the bathroom when he was younger than 5 years old.

He would be taken into the shower and made to touch his father inappropriately. It soon escalated into rape, where the son was made to perform other painful sex acts.

The son described years of childhood torture in the Palmerston North District Court on Friday, as the man who inflicted it upon him was sentenced to 18 years behind bars.

The father, who is connected to the secretive Exclusive Brethren church, still denies sexually abusing his son.

The offending even ventured outside the family home, with the son saying he was raped and violated at a beach and in an alley behind his father's work.

On another occasion, the father sexually violated him at his grandparents' home.

He struck his son with his hands and boots, and used a large wooden spoon to dish out punishment.

Now 26 years old, the son said he had made several attempts to take his own life and spent time in a mental health facility at Palmerston North Hospital.

"I became dependent on medication, and later alcohol and drugs. But it never helped," the son said, as his father sobbed in the dock, his head buried in his hands.

"I have a deep-rooted fear of men. I hate them coming near me. I'm scared to have children and my thoughts are that it is better not to continue the bloodline."

The son told the court he suffered from regular flashbacks. Some were spurred by seeing people in the street who looked similar to his father.

Others were triggered by sheds or vehicles, reminding him of when he was locked in a chicken coop and the trunk of a car.

"It has been hard carrying this horrible secret with me all these years. I have lost all hope that I will ever hear the word 'sorry'."

Crown prosecutor Michael Blaschke said the man engineered opportunities to carry out his sexual assaults, such as father-son excursions to the beach.

The offending was vile, repetitive and sustained, he said.

"It dominated the victim's life. He brutally offended on repetitive occasions."

Defence lawyer Fergus Steedman said the father admitted he was a terrible parent and acknowledged his son's childhood was "miserable".

"He always hoped he could step up to the mark. That he could try to be a good father."

Steedman said the church didn't approve of the man's parenting.

Judge Jim Large said the complainant had an appalling childhood, which had affected his adult years.

Large said the father did whatever he pleased and described the family home as a "reign of terror".

"You simply did what you wanted to do, when you wanted to do it, for your sexual gratification.

"He has grown up without the usual love, care and respect that children are entitled to from their parents."

It took two trials to reach a verdict, with a jury in December 2016 hung on all charges.