Kieran's stepfather John Barnaby explained the dangers of swimming at West Coast beaches upon arrival, Coroner Shortland said.
Mr Barnaby described the conditions on the day as "reasonably calm" and estimated the surf was around one meter in height. He observed there was a current but it did not appear too strong.
The boys were playing on the sand dunes while Mr Barnaby and another adult were fishing close by. When Mr Barnaby saw the boys had taken off their shirts, and in Dillion's case rolled up his jeans, to paddle in water up to their knees he told them not to go any further.
After turning around to check his rod, the boys had disappeared.
The boys had been hit by rogue waves and "very quickly" pulled out by the rip and current, Mr Shortland said.
"Dillion wearing jeans would have exacerbated the situation and made it more difficult for him to stay afloat," he said.
The jeans had returned to full length.
While Kieran tried multiple times to keep Dillion above the water he kept going under. In his evidence to Mr Shortland, Kieran said Dillion encouraged him to swim to shore for help which he ignored in trying to help his friend.
The boys were separated by a wave and Kieran did not see Dillion again. Mr Barnaby managed to rescue Kieran but could not find Dillion.
Onshore the alarm had been raised with two local surfers, the coastguard and a helicopter putting in a "frantic effort" to find him.
Dillion's body was found by the rescue helicopter about five or six kilometres from where he entered the water.
"There was nothing more that could have been done other than not enter the water at all to prevent this tragedy," Mr Shortland said.
On December 28, 2013 two men drowned and another was rescued just north of Maunganui Bluff while fishing off rocks.