Trowell then showed his class to pick up one point on End 11 and two points on End 12 for the victory.
He will travel to the New Zealand under-18 finals in Porirua this year. In an initiative brought in last year, the runner-up, Matthew Foster, will also get to contest the NZ finals.
Trowell has now won this local event three years in a row.
In the local final of the New Zealand Henselite singles against 15-year-old Dylan Foster, Trowell was in command from the start.
After five of the scheduled 15 ends, he was 7-2 up. By the ninth end, he was 12-4 up.
The players shook hands after the 13th end. Trowell had picked up four shots on that end to be unbeatable at 18-7 up. This was his 17th centre title.
Trowell has won the local final of this prestigious event three times in the past four years.
He will contest the zone finals against bowlers from Waikato, Thames Valley, Tauranga and Bay of Plenty in July.
If Trowell wins the zone final, as he did last year, the New Zealand Indoor Bowls Federation will pay his airfares and accommodation for the national finals in Dunedin.
Warren Gibb, Bruce Easton, Pauline Stone and Lois Lamont won the local final of the New Zealand Masters Fours.
It was played on a two-life system against Arnold Hutchins, John Harvey, Bryan Pulley and Kevin Lee.
In the first game, Gibb's team was all class, winning the nine-end game 10-3.
This took a life off Hutchins' team.
In a see-sawing second game, Gibb's team were 5-4 up after six ends, but Hutchins' team struck back with two points on End 7 and one point on End 8 to go into the last end ahead 7-5.
Gibb's team could score only one point on the last end, meaning Hutchins had won and taken a life off Gibb's team.
In the final game the scores were locked at 4-4 after six ends.Gibb picked up two points on End 7 but on End 8 Hutchins played a great bowl to collect four shots to be ahead 8-6 going into the last end.
On that last end, Gibb played a top bowl to pick up the kitty for three shots. Hutchins played too wide with his last bowl, and Gibb held the three points needed for victory. His team will contest the zone final against Waikato, Thames Valley, Tauranga and the Bay of Plenty in Whakatane in July.
The winners go through to the New Zealand finals in Auckland in late August.