You're correct with one small correction. He does not really care who jams the rudder, just that it gets jammed up. 
This is what Tyrhallan thinks:
He'll try to break into the wheelhouse of the central frigate.
Once in control he'll try to change the course, aiming for one of the other frigates.
In order to stop them from stopping them, they'll need to jam the rudder and set fire to it.
 
It is an old tactic called fireships, turning whole fleets to the torch. Though back in the day it was dependent on wind and an element of suprise.

Apart from it possibly taking out both ships, it will also cause new problems for the Vaimese force, after all. 
Can't fight a war when your in disarray because of collisions and burning vessels.
It will also for the mages to focus on dealing with the fire first. 
Less time they have for us, less time they have to think and counter our attacks.
The more time we have to deal with them, picking them off one by one.