yes, tusk failed his save, you can ride the eidolon outside of combat by hanging on.
[sblock=OOC]damages and statuses: 2 damage from the rocks, climb checks are DC 15, swim checks anywhere near the rocks are DC 20 with the waves smashing against rocks
for beach searching:
you do not find much fresh water but there is a small stream, and there are plentiful caves, but they will be difficult to get to, maybe with a little rope a bridge could be created to get to them and you know that there was rope on the boat...[/sblock]