EDIT: I deleted my post questioning the validity of a normal tack counting as part of a penalty.

This is covered by Case 108 (ISAF website). It starts with 44.1(b) as I mentioned above (if you gained an advantage by breaking a rule, in this case touching the mark, you must retire). Also, as stated by others above, a tack at the weather mark may be counted as one of the two-turns.

Personally, I don't see how this can be construed as a "penalty" but that's not what the rule gods have come up with.

Mike