29 July 2012 Last updated at 09:32 ET

River Avon bathtub world record attempt is under way

The two men are raising money for the Alzheimer's Society and the Portishead Lifeboat Trust

Two men are trying to set a new world record by paddling 17miles (27km) down the River Avon in bathtubs.

Rob Knott, 40, from Portishead, and Ric Canham, 56, from Axbridge set off from Bath Marina at 06:00 BST and hope to reach Bristol Marina at 16:00 BST.

The two have been training to master the skills needed to stay upright on the water in the baths.

They are raising money for the Alzheimer's Society and the Portishead Lifeboat Trust.

'Wacky endeavour'

"We've had a few days now without heavy rain," said Mr Knott.

"Having a reasonable flow in the Avon will help us go more quickly - but you can have too much of a good thing."

A fallback course has been mapped out in the case of dangerous conditions, which takes the pair out of the fastest flowing parts of the river.

Their challenge has been given the backing of actor and Alzheimer's campaigner Tony Robinson - known for his portrayal of Baldrick in the BBC comedy Blackadder.

"Helping people with dementia is something very close to my heart," said Mr Robinson.

"I want to wish the team all the very best and ask everyone out there to support this wacky endeavour in any way they can."

"I took up this challenge to raise money to beat a disease that claimed the life of a dear friend," said Mr Canham.

"Every penny raised can make a difference to two really important causes."