"It kept swimming through the berley trail and then coming up against the back of the boat and having a bit of a go at the propeller.
"It put its nose up on the back of the platform, just on the back of the boat at one point as well."
Mr Robertson has been fishing for about 25 years and said he'd never seen a shark "that size" come up close.
"We do a lot of fishing.
"To have it 100 metres out from Tiritiri Matangi's wharf, where the ferry goes, and in 20 metres of water in a gulf was just amazing."
It swam off once it lost interest, he said.
"We were a little bit more cautious than we usually would be when leaning over and washing your hands in the water after baiting your hook - we certainly weren't doing that."
Department of Conservation marine scientist Clinton Duffy confirmed from Mr Robertson's photo the shark was a juvenile great white.
A video taken by Mr Robertson showing it swimming around the berley trail was "very typical", Mr Duffy said.
"The shark has simply followed the scent to its sources and is investigating the boat to see where the smell is coming from and if there is anything edible there."
Interest in the outboard motor, which was removed from the water by Mr Robertson after the shark kept nudging it, was also not unusual, Mr Duffy said.
"Once at the boat, sharks of all species can be strongly attracted to outboard motors and anodes attached to the hull by the weak electric field these generate in saltwater."
Smaller great whites were often found in coastal waters around the North Island because of their feeding habits, Mr Duffy said.
"It's quite a small one, and they're mainly seen in coastal, shallow waters - right up in harbours.
"They feed primarily on fish at that size and ... there's a lot of fish in those places," he said.
