Two childhood friends are training for an adventurous challenge that will see them sail across Scotland in a bathtub.

Mark Brockway and Jack Burrows have known each other since they were eight years old - a friendship that will be tested to its limits when the 6ft pair spend seven days rowing 77 miles across the Caledonian Canal.

On August 13, the intrepid outdoorsmen from Luton, Bedfordshire, will launch their unusual vessel from Corpach near Fort William to Loch Lochy. They will head north east using canoe paddles at a speed of 1.5mph, where they will eventually sail the length of Loch Ness before berthing in Inverness.

The bathtub itself has only minor modifications - some piping for buoyancy and a coat of resin to prevent rot - which may make for an interesting voyage, battling 3ft waves on Scotland's largest loch.

The plan was hatched over a number of years to raise money for the Bedford MS Therapy Centre, a charity that cared for Mark's father Richard when he contracted the disease.

Mark fondly describes his father as an "obsessive runner" who passed on his love of the outdoors during father-son hikes, whatever the weather.

When it manifested around ten years ago, the condition first affected Richard's legs, causing him to fall during his runs and eventually, stripping his ability to care for himself. He died in May this year, aged 69.

Mark said: "My dad was a great man, an absolute nutter and a real character. He lived to make other people happy and was one of my closest friends.

"Dad showed an unbelievable level of determination and courage to fight against all the condition threw at him.

"It gave me great pride to support dad but, from our experience, MS as a condition receives relatively little financial support and that's something Jack and I feel passionately about trying to change. Rowing a bath tub across Scotland is hopefully just the start."

A geography teacher by day, Mark admits he is no utilitarian when it comes to customising the tub that will be his carrier for seven days.

Jack, an automotive engineer, has made most of the adjustments, based on advice given by Caledonian Canal staff and the RNLI, which was delighted to hear of their plans.

Mark said: "I'm really excited. We've had it in our head for years and this year it slotted into place.

"I'm slightly apprehensive but at the same time really confident. If we do fall in we have the equipment to cope and if the weather gets really bad we'll sit on the shore and hold out."

Jack and Mark have launched a crowdfunding page which has so far raised more than £2000 and is expected to break a target of £7000 as the popularity of their challenge increases.

The challenge is the first of its kind in Scotland and Mark is in talks with the Guinness World Records, hopeful the journey may warrant an accolade.

Members of the public have been invited to watch the pair take on the Scottish wilderness, which can be seen from the footpath along the Great Glen Way.

Mark added: "Our main aim was to raise as much money as possible for the MS Centre that so we thought the combination of a genuinely really tough challenge and an incredibly far-fetched idea that would capture people's imagination and attention would do the trick.

"We've had such a great response to the expedition with overwhelming support from those that know us personally and the general public. Also, I think we're breaking a world record for the first people to paddle the width of Scotland in a bath tub.

"I don't think we'll break any records time wise but we're determined to reach Inverness in one piece."