A Launceston fisherman and his son are trying to piece together why a shark - suspected as being a great white - attacked their boat near Tenth Island off Beechford on Wednesday morning.
Sean and James Vinar were making the most of the calm conditions by taking their 5.5-metre boat from Low Head to the island to observe seals about 9am.
Watch the footage below (Warning: explicit language):
But as they pulled up to film some video and take photos of the island, they were suddenly interrupted.
"We turned around and thought we'd just slow the boat down and have a good look at the island," Sean Vinar said.
"Next minute, there was just an almighty thump on side of the boat, this shark just flew out of the water and latched onto the side of the boat.
The location of Tenth Island, also known as Barrenjoey:
"I started to move the boat forward to get shark off the anchor, the entire mouth had engulfed the anchor, it was something you see on the TV, like a wildlife documentary.
"It was that big, I was concerned that if it started to thrash its tail it'd put a hole in the boat. We weren't sure if it bit into the side of the boat."
Fortunately, their boat sustained no significant damage and they were able to flee the area.
The pair's attention has now turned to why the terrifying incident occurred - particularly in light of the recent attack off Stanley, in which 10-year-old Lucas Arnott was dragged into the water by a great white shark.
Sean and James Vinar were yet to start fishing and were simply moving slowly in calm water.
Sean Vinar said seals started swimming towards the boat from the island just before the attack occurred.
"Whether that's what enticed the shark - it might've been following the seals swimming towards the boat - we don't really know," he said.
"It could've seen us as another predator - a bigger shark going after the seals, and wanted to take us, so it hit the side of the boat.
"I thought great whites would only be in a warmer temperature areas, I was just amazed, it was totally unexpected."
The CSIRO has been contacted for comment.