Mr Heseltine (42) and Ms Mc-Gregor (28) will marry tomorrow.
As skippers of the Otago Harbour wildlife tour vessel, both are used to taking a leadership role but say they plan to "share turns at the helm" in married life.
Mr Heseltine, who was a primary school teacher for 10 years, has worked on the Monarch for more than seven years, the past five as skipper.
Ms McGregor started with the Monarch five years ago following tourism training and has been a skipper for three years.
But it was a while before the Monarch became the Love Boat.
"We worked together for about eight months . . . after a series of tricky social situations, we began dating.
"We had our first date in Monarch uniform," Ms McGregor said.
This weekend's wedding will be at Stoneridge Estate, near Lake Hayes.
"Because we are both deeply entrenched with Monarch, we decided to marry in Central so that our wedding would be about us and not about Monarch," Mr Heseltine said.
The pair will be back at work in the middle of next week but will take a honeymoon later this year in Ms McGregor's birth country, Canada.
They plan to continue as skippers on the Monarch despite the stress the job places on a relationship.
"We get very little time off together and there is no escape from work, especially during the long hours of summer," Ms McGregor said.
But there were some definite positives, she said.
"We get to share exciting wildlife sightings, like the humpback whale sighting on Sunday this week . . .
"And we occasionally get rostered together which is fun."
They are also "study buddies" as they work towards Marine Engineer Class 6 qualifications.
And then there are the trousers.
"We can wear each other's uniforms if we get a little bit lazy with the laundry," Mr Heseltine said.
"Only one person was able to pick that I was wearing Rachel's trousers one day."
