Well, yes, the Hammerhead does get cover from anything outside of 12".
As far as the chimera goes, I hadn't actually done the math, but.....even with smoke launchers, not terribly worried about it.
Say the two vehicles start 24.1" apart. First turn 12" move, pop smoke, now it's 12.1" away (realistically, I can probably slide side ways get a little more distance, but whatever). Now the MMs can either stay there.......or not shoot.
My chance to "stop" a Chimera with a rail gun is 51.85%, obviously half that if they popped smoke. 29.63% chance to kill.
For the Ion cannon, it's 29.77% to "stop", 10.7% to kill, half with smoke.
This is assuming, in both cases that I don't veer to the corners, making him chase each hammerhead with each chimera, and I am then able to "cross the streams" and hit the other chimera in the side. (hint: terrain permitting, I can probably do that)
Now, conversely, each Multi-Melta, outside 12", has a 6.25% chance to "stop" (weapon destoyed and shaken aren't counted in this, but I don't feel like recalculating everything) and a 3.01% chance to kill the hammerhead (this is counting cover). WHHHHHHHHHEEEEEeeeeeeeeeeeee!!!!!!!!!!!!
Granted, he does have 6 meltas, but I just don't think it will even get to that point, and the chances are pretty low even if they do.
https://docs.google.com/spreadsheet/ccc?key=0AnFuN-yY7GTydDNHWnZMUHhXaGdkR3ZYQ1ZGQ2FabXc&hl=en_US&pli=1#gid=0I'm getting my data from this spreadsheet I started, but others have been collaborating on it since, so I'm not in complete control of it anymore. For instance, the Hammerhead Rail gun calculations under the "Tau" tab look to be just plain wrong, but I had separate calculations under the "calculations page" that I used.