Only the action of the quick-thinking crew saved lives from being lost on the MV Saoirse, which is docked in Turkey.
It was due to take part in a flotilla to the besieged Middle East zone but was "sabotaged" and will not now travel.
Rugby player Trevor Hogan said the realisation of what happened has left crew members "devastated".
He said the boat would have been "well out to sea" before the effects of the attack were felt.
"There would have been a loss of life on the boat. It's pretty devastating. We're all coming to terms with it at the moment," the 31-year-old former Leinster and Munster star said.
"It was definitely sabotage. It was a clear attempt to sink the boat and it would have been a gradual sinking."
The Israeli spy agency Mossad is being blamed for the sabotage.
Former TD Chris Andrews told the Herald today: "The boat would almost certainly have sank.
"We don't know the precise way they did it but they cut a shaft so that we would have got out of the port but then it would have snapped."
Divers used an angle grinder to cut the shaft while it was at berth in the Turkish coastal town Gocek.
Trevor said: "You don't need to be Sherlock Holmes to work out who is responsible for this. Israel is the only one who is interested in stopping this flotilla and they're using every means possible. It's pretty worrying."
He wants the Irish Government to "stand up behind us and protect us" and called for Foreign Affairs Minister Eamon Gilmore to condemn the attack.
Six of the 20 crew and passengers who had been due to travel on the Saoirse will now join the flotilla on an Italian vessel.
"They're not going to intimidate any of us. Our resolve is stronger than ever," Mr Hogan said.
The Israeli Embassy in Dublin did not provide a response to the Herald regarding the allegations at the time of writing.
The Saoirse had been at berth in Turkey for the past few weeks. The damage was discovered when skipper Shane Dillon noticed something amiss and carried out an inspection.
The boat was put on land at a local shipyard and the extent of the sabotage was immediately visible.
"The propeller shaft had been weakened by saboteurs who cut, gouged or filed a piece off the shaft. This had weakened the integrity of the shaft, causing it to bend badly when put in use," said a press statement.
Dr Fintan Lane, national coordinator of Irish Ship To Gaza, which owns the vessel, said: "This is an appalling attack and should be condemned by all right-thinking people."