it is not the LaW of the Sea, but the San Remo Manual on International Law Applicable to Armed Conflict. The UN report on last year's convoy declares the blockade legal, but people like Mise Eire don't care about facts--nor do they care that Hamas itself declares that there's no humanitarian crisis. The additional fact that this pleasure yacht carries no humanitarian aid also has no wieght with Mise Eire, just the "illegal blockade" that isn't illegal...except in his/her mind.
Hamas says Egyptian mediation has restored calm along Israel, Gaza border (Haaretz)
from the article: Israel Navy warns last remnant of flotilla not to approach Gaza shore