It was by far the worst ride of his trip across the Tasman, Mr Funnell said.
Donaldson had been drifting south-west at a speed in excess of 1km/h due to the combination of a strong current and gale force winds.
"He's getting a hell of a thrashing out there, so much so that it's actually broken one of his harnesses inside that restrain him."
However the rough night hadn't put him off his mission, Mr Funnell said. "He's going to keep going."
"We've got gale-force winds out there. It's fair to say that we're looking forward to the end of it and the weather to improve.
"We are a little bit concerned, it's very violent out there.
"I was talking to a helicopter operator on the West Coast and he said it's been a hell of a night over there."
Donaldson's cabin was watertight and he had a bilge pump if any water did get in, Mr Funnell said.
"The kayak is robust...but the issue is, even though it's a small cabin, he's inside it - it's like being a dice in a cup - you're getting bashed around in there.
"Hopefully that weather will abate through the course of the day."
Donaldson was expected to reach land sometime next week "at the earliest", he said. As a result, another supply drop would be needed.
"I think the plan is to send a boat out to take some more supplies out to him...hopefully [on] Saturday morning. This weather system is proving challenging."
This is Donaldson's second attempt to cross the Tasman, after his kayak filled with water two days into his his first attempt in May last year.
He is making the trip to raise awareness for Asthma NZ, an illness both he and his 4-year-old son suffer from.
He is also hoping to highlight the importance of increasing aerobic activity levels in our day to day lives.
Mr Funnell said he had never met the kayaker and only became involved in the mission after Donaldson's wife Sarah appealed for him to help.
"His wife rang up and said 'my husband's kayaking the Tasman and he's run out of food'."
He had conducted three supply drops to the kayaker to-date, he said.
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