An Australian man whose wife disappeared while they honeymooned at sea has been sentenced to eight years in prison for involuntary manslaughter.

Lewis Bennett, 42, apologised to the family of Isabella Hellman during a hearing before US District Judge Federico Moreno in Miami on Tuesday. He waived his right to appeal.

Bennett was originally charged with murder, with investigators alleging he intentionally tried to sink the boat, but later dropped the charges.

Bennett, a dual Australia-British citizen, had asked the judge to let him out of prison sooner so he could raise the couple’s daughter, who turns three in July and is being raised by Bennett’s parents in Scotland.

“If you may permit me to be with my daughter as soon as possible,” Bennett said. “I want to bring her up in a manner that is respectful to my wife’s wishes.”

But Judge Moreno sided with prosecutors and chose eight years in prison as the sentence and three years on supervised release.

Ms Hellman disappeared as the couple sailed off the Bahamas in May 2017.

A statement from the US Attorney’s office said Bennett had experience sailing, including training on emergency procedures, and had previously travelled from St Marteen to Australia.

His wife, a naturalised US citizen born in Cuba, had not trained in emergency sailing procedures and had less experience.

The catamaran Surf into Summer, which Lewis Bennett and wife Isabella Hellmann were sailing on before her disappearance. Photo: AAP

The couple had been married for three months when they set sail to St Marteen, Puerto Rico and Cuba for a delayed honeymoon in late April.

After they left Cuba on May 14, Bennett asked Ms Hellman take over control of the boat for the night so he could go rest in the cabin, according to court documents.

He didn’t require her to wear a life jacket, harness or personal locator, prosecutors said in the statement.

He said he woke up when the craft hit something. Ms Hellman was missing.

The government maintained he didn’t use the satellite phone to call for help. Instead, he loaded provisions and stolen silver coins onto a life raft and boarded it.

Prosecutors said he called for help 45 minutes after he had woken up realising his wife was gone.

The newly-wed couple was sailing this catamaran off the coast of Cuba when Ms Hellman disappeared. Photo: AAP

A US Coast Guard helicopter rescued him; authorities searched for Ms Hellman for four days, but never found her body.

A Florida state judge declared Ms Hellman dead earlier this month, clearing the couple’s daughter to inherit her mother’s estate.

“Hellman’s death occurred as a result of Bennett’s knowledge of circumstances that existed that could have reasonably enabled him to foresee threat to life,” the US Attorney’s office said Tuesday.

The FBI said an inspection found that holes in the boat’s hull were inflicted from the inside and hatches were opened in a deliberate attempt to sink the boat.

Bennett was initially arrested and charged with murder last year before reaching a plea deal with federal prosecutors. He had already pleaded guilty to transporting $US100,000 ($A144,340) in stolen coins.