That doesn't look like much of a bomb. I'm no expert, but I don't see wires, and the twist tie top looks not too water proof. It looks more like a ruse.
This looks exactly like the bomb found floating Tuesday of last week ( wednesday is when the ferry blew up). That one had 7 dynamite sticks wired to a controller with antennae for remote detonation. These on the rudders were either dummies or had motion activated detonators, since no antennas were seen.
Dave