The Ship Inn, in Langstone Road, Havant, will be hosting a raft race around Emsworth Harbour at 2:45pm.
More than 15 rafts will be entering the race, the largest number of entries in the event's six year history, according to landlord Mark Dawson.
He said: '’Previous years have seen the rafts go about out about 100 meters into Emsworth Harbour, do some turns, and come back - this year we wanted to make it more of a challenge, because the guys put so much effort into their rafts.
'So we have added lots of figures of eight.
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'It's going to be carnage.'
The event is held to support the Royal National Lifeboat Institution, with money being raised through raft crews paying an entry fee, as well as a pitch-and-put and tombola taking place across the day.
More than £1,000 has been raised for the lifeboat charity, with members of its search and rescue team in attendance at the event.
Mark added: 'They have come down to enjoy the day - hopefully they won't be needed to do any rescuing.'
Awards, including beer and sparkling wine, will be handed out to the fastest four-man and six-man or more crews at 4pm.
Visitors will be able to enjoy a BBQ and live music until 6pm, with a Tiki bar serving special cocktails remaining open until 9pm.