It is not clear that the ICJ will hear an appeal by Turkey if Israel refuses to abide by the decision. The way to involve the ICJ is for Turkey to get the UN General Assembly to request an "advisory opinion" from the ICJ on whether the naval blockade of Gaza is legal or not. One legal claim could be that Gaza is an occupied territory and thus Israel is only entitled to prevent ships from entering its territorial waters, but not to forbid shipping in international waters. The fact is that the status of the Naval Blockade is controversial (as is the status of Gaza occupation). The Parker commission was not of legal authority, and its determination was based on opinions by the two sides. The ICJ has a respectable legal standing and its opinion will be authoritative.
Thousands gather in Kuala Lumpur for rally urging Malaysian leader to quit (AP)
from the article: Turkey to refer Israel's blockade of Gaza Strip to The Hague