At the most, they expected to be out for an hour or two before heading home for a bite to eat.
But Michael McGrath and Gary Aiano were recovering today after being rescued following a harrowing 28 hours at sea in their speedboat.
They had no food and little water when they set out and could not make their mobile phones work.
To make things worse, they drifted into a busy shipping lane and narrowly avoided hitting vessels which dwarfed their 20ft craft.
Coastguards said the pair were "incredibly lucky" to have been found.
Mr McGrath, who lives at Brighton marina, and Mr Aiano, from Crowborough, had just left the marina in the Southern Belle on Thursday evening when the engine failed.
The radio on board Southern Belle was not working and neither man could raise anybody ashore using their phones.
Neither had they told anybody where they were going and they were not reported missing as they began to drift into busy Channel shipping lanes as night fell.
The wind picked up to force four to five as the pair drifted through the night.
As the sea became rougher and they began to suffer from seasickness the two men thought the Southern Belle might capsize.
In the darkness, they nearly collided with a cruise liner as they were blown out to sea by offshore winds.
They managed to get the engine started again after dawn on Friday and headed back towards the coast, only to run out of fuel after 15 minutes.
At about 10am, still drifting helplessly, they spotted the Swedish-registered freighter Bro Nelly nearby and fired one of their two distress flares.
Coastguards said the Bro Nelly refused to come to their aid, saying one of its lifeboats was not working and the other was too small to help.
The two men tried to attract the attention of other vessels passing in the distance by waving their arms in the air but were not seen.
It was not until 3pm on Friday, 24 hours after they set off on their ill-fated cruise, that a second cargo ship passed close by.
They were spotted by the Cypriot-registered Axion as they fired their remaining distress flare.
The Axion alerted Dover Coastguards and turned to help the stricken pair, who by now were about 13 miles south west of Beachy Head.
In a difficult manoeuvre the Axion went alongside Southern Belle and hauled the exhausted men on board using a rope ladder.
They were collected by Eastbourne lifeboat, which brought them, together with the stricken Southern Belle, back to Sovereign Harbour at Eastbourne.
They returned to dry land at 7.45pm, nearly 29 hours after setting off.
Mr Aiano, 32, who is single, said afterwards: "We were just planning to go out for a few hours.
"I think we had a lot of water in the engine and that was what caused the problem. We started to drift out of sight and there was nothing we could do.
"Michael's phone had water damage and I managed to block my pin code. It was just a catalogue of errors."
He said the pair had learned their lesson and had now packed the boat full of lifejackets, anchors and flares.
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