Help was only a phone call or a few minutes' walk away, but Guy Appleton did not seek it as his friend, Clayton Graves, lay dying in a crashed boat.

Today, Appleton, 45, was jailed for the manslaughter of Graves, 29, as a court was told of what happened on their fateful midnight fishing trip in Tauranga.

The court also heard from Graves' mother, Lisa Graves, about the "immeasurable" pain of losing her only child.

Through tears, she said what Appleton did was "unthinkable".

"[To] just leave my son to die of his injuries, to bleed out cold, wet, alone, in pain, frightened and scared. To not attempt to call for ... medical help for my only son.

"You sat on the rocks for over six hours until a passer-by stopped ... What kind of mate, son, brother and father does that make you?

Clayton Graves was 29 when he died. Photo / File

"You have robbed me of seeing my son marry, become a father, look after me in my old age. You have robbed his friends and family of his wicked sense of humour, his cheeky laugh, his melt-your-heart smile, the good and bad times that would have been part of all our lives.

"You took away our chance to see him alive and to say our goodbyes if medical assistance had been sought."

According to court documents, Appleton, a builder, and Graves, a building apprentice, met at a building site a couple of years earlier and became friends.

Both had been drinking when they decided to go fishing in Appleton's 5m aluminium boat, named Apples, late on October 4, 2019.

Appleton was at the helm when security cameras captured them motoring away from the Sulphur Point boat ramp on the high tide at 12.44am, with no navigational lights to be seen.

The weather was fair with a moonlit, cloudless sky.

Shortly before the crash, Appleton was speeding at 23 knots or 42.4km/h in an area with a 5-knot limit - within 200m of shore or an object.

The court was told Appleton was likely disorientated by the bright lights of Tauranga City and the Port of Tauranga as he cut a corner.

The boat crashed into Stoney Point - a rocky outcrop from Mauao where the statue of Tangaroa stands - and hit a beacon about 1.14am, according to the documents.

The hull of the boat was not pierced when it crashed into rocks. Photo / File

Appleton and Graves were thrown forward, hitting the front of the boat and smashing the perspex windscreen.

Graves was thrown into a horizontal handrail and suffered major internal injuries: a torn inferior vena cava; rib fractures; tears to his liver and left kidney.

Appleton managed to get the disabled but still floating boat to the beach at Pilot Bay.

The hull of the boat was not pierced when it crashed into rocks. Photo / File

Graves, bleeding internally and only wearing his underwear, was said to have crawled into the boat, where he succumbed to his injuries and died.

Appleton sat on the beach for the rest of the night. He did not have his phone and the boat radio was not working. The court was told he also did not use a first aid kit or flare in the boat.

Graves' phone was protected by a pin number, but Appleton still could have used its emergency function to call 111 without unlocking it.

Appleton was dazed, confused and hypothermic. He did not seek medical help despite it being a five-minute walk away.

Just before 7am, passers-by began noticing the boat.

One photographed Appleton leaning into it. Another pair asked him if he was alright. He said he hit a rock, answering "yeah" when asked if he was waiting for the tide to come in.

At 7.45am, a witness noticed Graves. His face was "smashed up and foam coming from his mouth". The witness shook Graves but there was no response and his body was stiff.

He saw Appleton resting against a hill nearby and called to him "are you okay, how's your mate?"

Appleton replied: "He's fine, he's asleep." The witness found someone with a phone and called for help.

Emergency medical staff who came to the scene believed Graves had been dead for about four to six hours.

Appleton's blood alcohol on admission to hospital was 20 milligrams of alcohol per 100 millilitres of blood. Scientists would later estimate his level at the time of the crash at 110-220 milligrams per 100 millilitres.

Authorities concluded Appleton had "captained his vessel irresponsibly" and made "a series of poor decisions and actions in breach of Maritime New Zealand guidelines and Maritime Rules".

"These actions and omissions resulted in the crash and the subsequent injuries sustained to the deceased which resulted in his death."

Appleton was charged with manslaughter, causing Graves' death by failing to adhere to the provisions of the Maritime Transport Act.

He initially elected a trial but pleaded guilty in October.

In the High Court at Tauranga today, defence lawyer Fraser Wood said Appleton remembered little of what happened after the impact.

He said Appleton was injured in the crash and was clearly not thinking logically or understanding the seriousness of Graves' injuries.

"He thought he was just sleeping. That goes a long way to explain why he didn't do anything."

He apologised to Graves' family on Appleton's behalf and said his client was genuinely remorseful, though had difficulty showing it.

Judge Christine Gordon said Appleton's "behaviour went beyond carelessness, it was reckless".

She accepted he was harmed in the crash but said he was not diagnosed with a head injury and failing to seek help was an aggravating factor.

She sentenced him to two years and seven months' imprisonment.

In a statement after the sentencing, Maritime NZ said skippers were legally responsible for the safety of the boat and everyone on board, and Appleton made a series of poor decisions that led to the tragic event.

"As this incident clearly highlights, boating and alcohol do not mix.

"Things can change quickly on the water. You need to stay alert and aware."