Duncan achieved an amazing 34th place out of 180 in his 30 to 34 age group and 171st overall out of 2,346 participants.
An Ironman competition involves a grueling 3.8 km swim, a 180km cycle followed by a marathon run of 42 kms, all completed in temperatures of up to 40 degrees C and draining high humidity.
The 2,346 starters, who were mainly amateurs, all had to qualify from races held throughout the year.
Duncan achieved one of the four qualifying slots in his age group from the Austrian Ironman event.
What is impressive is Duncan only started competing four years ago with the Hawaii race being only his fifth Ironman.
Duncan found the swim was the biggest challenge.
With 1,500 other competitors setting off at the same time the first half of the swim seemed “more of a fight for water than a swim”.
Duncan incurred a five-minute penalty time in the cycle section as there are strict racing rules meaning there must be a 12-and-half metre gap between you and the person in front unless you are successfully overtaking.
Duncan therefore had time and places to make up in the last event but he ran an incredible marathon.
Duncan was supported in Hawaii by wife Lauren and back home in Stonehaven by parents Andy and Linda.
As all competitors wear an ankle tracker they could watch Duncan’s progress online with times and placings recorded at each transition point.
Duncan finishes this year an impressive third in his age group in the UK and 22nd in his age group in the 2017 Ironman world rankings.