That other day I hit some driftwood, and near the pivot hole, a 2 inch piece broke off.

I was under the impression that the centerboards kick up with only minor damage. It did not kick up this time, instead the pivot tube broke out of the hole.

Am I just unlucky, or is this something that may happen once in a while?

It feels like I do a lot more repairing than sailing recently...

kind of like gearing

the closer the impact point to the pivot hole the less chance the whole board has of moving away from the object to avoid damage. too close is too highly geared

imagine the damage if it had been a vertical daggerboard in an eggshell casing

i hit a floating 2x4 last year.. dented both bows, did a fair amount of damage to 1 of the centerboards, broke the centerboard track (very hard to get to for repairs) and even damaged the aft wall of the trunk because the centerboard slammed into it.

It also made a hell of a loud noise. I saw the board at the very last second (as it had grass covering it, and i wasn't really looking)... sure wasn't fun..

Comes with the terirtory..... boat ownership = repairs