As they were boating along the remote Wairaurahiri River in Fiordland National Park on Wednesday, they ran into a submerged log, which tore through the boat "like a can opener".
The pair had their life jackets on and nobody was hurt in the accident, but items spilled out of the boat through the gaping hole.
They were travelling in a group and friends nearby were able to assist.
"Thanks to all who helped us out," Marshall said.
"Good to always travel in a group when negotiating challenging rivers. Safety in numbers.
"Amazing river and scenery, and as Robbie commented, 'We will be back'. But maybe not until next year."
The boat was taken off the river and a helicopter was called in to remove it.
Wairaurahiri Wilderness Jet owner Paul Roff came across the wrecked boat on the river near Rabbit Flat.
"As we were boating back up stream from the Waitutu Lodge we noted a fuel drum floating down the river," Roff said.
"We slowed down and picked it up, then a bag of clothes, then a sleeping bag [and] another bag of clothes. But when a seat out of a jet boat arrived my thoughts changed to, 'This is bloody serious'."
As they came around the corner they found Deans and Marshall.
"No one hurt but one private jet boat opened up like a can opener."
Roff said it was important people checked their boats and safety gear before going out.