AN SMA PLT; CONCERNED ABOUT FOG BELOW; CLBED INTO THE SFO CLASS B AIRSPACE WITHOUT CLRNC.

Narrative

WX BRIEFING FROM UKIAH TO WATSONVILLE ALERTED ME TO PRESENCE OF FOG ALONG MY RTE AND TO SOME EXTENT INLAND; AND THAT'S SOMEWHAT NORMAL ESPECIALLY ALONG THE COAST. DEPARTING UKIAH AT XA00 AM FOR THE 2 HR FLT AND EXPECTING CLRING OF THE FOG AS I PROGRESSED; I WAS EXPECTING AN EASY FLT. MY FLT PLAN CALLED FOR USING THE SGD VOR OUTBOUND; ON THE 125 DEG RADIAL AT 5500 FT WHICH WOULD TAKE ME THROUGH THE I SECTOR OF THE SAN FRANCISCO CLASS B AIRSPACE UNDER THE 6000-8000 FT ALT. AS I APCHED THIS AREA; THE FOG WAS HIGHER AND MY GLIDING DISTANCE TO CLR GND; VISIBILITY BENEATH ME INCREASED AS THE FOG WAS MORE TO THE E THAN ANTICIPATED. FOR SAFETY; I CLBED TO 7500 FT AND TURNED TO THE E AND ALIGNED MYSELF WITH THE 120 DEG RADIAL THINKING THIS WOULD BE ENOUGH TO DIVERT THE CLASS B AIRSPACE ALTOGETHER. AT THE SAME TIME; I RADIOED CTR FOR FLT FOLLOWING. I WAS INFORMED THAT I WAS UNAUTH TO BE IN CLASS B AIRSPACE. I REPLIED I WOULD DROP ALT AND HE REPLIED TO CONTINUE AT PRESENT FLT LEVEL; 7500 FT. PART OF THE PROB WAS NOT BEING ABLE TO SEE HWY 680 THAT HELPS DEFINE THE EASTERN PART OF THE AIRSPACE. MT DIABLO SITS JUST OUTSIDE THE I SECTOR AND I THOUGHT I WAS CLOSE ENOUGH; BUT THAT WAS NOT THE CASE. IN RETROSPECT; I SHOULD HAVE GONE AROUND THE MOUNTAIN INSTEAD OF CUTTING IT TOO CLOSE ON THE WESTERN SIDE. BEING UNSURE OF MY POSITION OVER THE GND; A CALL TO ATC FOR CLRNC BEFORE ENTERING CLASS B WOULD HAVE BEEN MOST PRUDENT.