Human rights activists trying to break the Gaza blockade have vowed to stop Israeli forces from boarding their ship.
Dr Fintan Lane, coordinator of Irish Ship to Gaza, said crews in the second aid flotilla will make it difficult for officials to seize control of vessels, including the Irish-owned MV Saoirse.
Nine people were killed last year when Israeli commandos stormed the MV Marmara, a Turkish aid ship trying to break the naval blockade.
"If they attempt to board the ship we will non-violently impede their progress. We will not facilitate their boarding party," said Dr Lane.
"We will not lay hands on them, we will not use physical measures against them. But we will lock down the ship and make it difficult to seize control."
At least 20 Irish citizens, including former rugby international Trevor Hogan, are taking part in Freedom Flotilla II.
About a dozen aid ships carrying medical supplies, sports equipment and construction materials are due to meet in international waters some 16 hours from Gaza early next week.
Crew include skipper Shane Dillion, artist Felim Egan, former politician Chris Andrew and MEP Paul Murphy. Almost 130,000 euro has been raised in Ireland to fund the humanitarian mission.
Hogan, who recently retired from rugby with a knee injury, said he was focused on getting to Gaza but had to be prepared for the alternative. "Anything we face is a fraction of what the Palestinians face on a daily basis and that gives me strength," he added.
Dr Lane said threats by Israel to attack ships with snipers should be condemned by governments, including Ireland.