The Israel Navy can and has, ordered the ships to halt for inspection, which, even in WW2 Allied ships did to neutral flag ships headed for Axis ports and when they didn't obey, the ships' were disabled by firing at the rudder and then, the crews were given time to abandon the ship to their lifeboats, or were picked up and taken to the next allied port were they were interned. Then the ship would be sunk. Israel could do the same as she is at war. But I would not sink the ships, I would tow them to an Israeli port, turn over any military equipment to the IDF, any foodstuffs or other items such as clothing or blankets, I would have distributed to the appropriate social organizations for distributing to Israel's poor and then, as a warning to marine insurers, I would tow the ship out to sea, and have the Israel Navy and Air force use ti for target practice.
Kerry: Pollard's parole not related to Iran deal (Reuters)
from the article: Israel prepping to block next Gaza flotilla