Four commercial fisherman from New Zealand took the ride of their lives attempting to cross the Grey River's dangerous bar in rough waters.
Eager to return home after a one-week fishing trip, the captains of both ships decided to risk the crossing.
The current and waves were so strong it was difficult for the fishing boats to advance.
The washing machine effect was caused by pressure waves created by a flooded river surging into agitated seas.
The Auckland Coast Guard said the fishermen were lucky to have made the crossing unharmed: "They've got a risk of the boat being turned sideways and once that happens it's pretty easy to tip them over."
He added that only the most experienced seamen could navigate the notorious bar.
The fishermen did not break any laws crossing the bar despite a breakwater warning signal flashing in Greymouth port on their arrival.
Ten years ago, two fishermen died while crossing the bar under similar conditions.