Hello.

A little bit more information would be nice.
If you use chameleon or pc-efi you could set.

<key>Default Partition</key>
<string>hd(0,1)</string>

in /Extra/com.apple.Boot.plist

You find out the right Disk/Partition with the command "diskutil list" in Terminal
Just enter the Disk you want as default.

I hope this is the Information you needed, else I need more information on you System Configuration and Bootloader used.

EDIT: Since you are using Grub as Bootloader you maybe find the Solution there
>> http://discuss.extremetech.com/forum...004322173.aspx

gl