Sam Greenhill and Jamie Bennett hope to sail the four-mile stretch of water to raise hundreds of pounds for charity.
The pair, who are both graduating from University of Portsmouth this summer, devised the scheme two months ago while sinking a few pints in the Hole in the Wall pub in Great Southsea Street, Southsea.
Sam, 22, of Kent Road, Portsea, said: 'We first thought of the idea when we were in the pub. I wanted to do something to raise money for Great Ormond Street Hospital.
'I was in and out of the hospital for the first five years of my life because my heart wasn't working properly.
'It's about giving something back.'
Sam said 800 beer cans – most filled with foam – had gone into making the raft in his back garden. 'It has taken a lot of beer-drinking but we've had plenty of help from mates,' he said.
'Some of the cans are filled with foam and we've sealed the rest up with tape.
'We've also used old industrial drums to give us extra buoyancy.'
Expert help has been on hand from their friend John Holmes, who works as an engineer for BVT shipbuilders in Portsmouth.
Coastguard have given the friends the green light to make the crossing from Lepe beach, Calshot, to Cowes, Isle of Wight, on Sunday at 1.10pm.
Nigel Guyll, watch officer for Solent Coastguard, said: 'We've organised a Solent rescue boat to join them and they have met all the safety requirements so all should be well.'
Jamie, 20, a history graduate added: 'The raft's been built by an engineer so i'm pretty optimistic we can do it and we won't sink.'
£1,000 TARGETSam and Jamie have set their sights on raising £1,000 for Great Ormond Street Hospital Children's Charity
The London hospital treats around150,000 children from all over the UK every year
It also pioneers research, discovering and developing treatments for complex medical conditions such leukaemia and autism.
Great Ormond Street Hospital was the first institution in the UK to offer inpatient care to children only
The two graduates have raised £815 so far through their online fundraising webpage.
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