C185 FLOAT PLANE WITH 2 PLTS ENTERS CLASS B OF SEATTLE DURING SOME DEVIATING AROUND WX. PLTS WERE USING GPS 'DIRECT' FROM OLYMPIA TO FRIDAY HARBOR TO POWELL RIVER. PF ADMITS THAT HE SHOULD HAVE BEEN ON SEA APCH CTL FREQ.

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CRUISING AT 4500 FT PAST OLYMPIA; WA; OVER BROKEN OVCST; VISUALLY OVERFLEW BELFAIR; WA. STARTED CLB TO AVOID BUILDUPS WHILE FLYING A GPS HDG TOWARD FRIDAY HARBOR. CONTACTED WHIDBEY APCH ABOUT JEFFERSON COUNTY INTL. WAS TOLD BY WHIDBEY THAT CTR SAID WE HAD ENTERED CLASS B AIRSPACE. I DON'T BELIEVE I DID THAT. WOULD BE EDUCATIONAL FOR ME TO REVIEW THE RADAR TAPES. SUPPLEMENTAL INFO FROM ACN 378809: VFR FLT PLAN FROM AURORA STATE; OR; AT BTWN 6200-6500 FT MSL DIRECT OLYMPIA; DIRECT FRIDAY HARBOR DIRECT POWELL RIVER; BC. AFTER PASSING OLYMPIA WE WENT TO A SOLID UNDERCAST AND BROKEN OVCST WITH BUILDUPS; REQUIRING FLT DEVS. BY THE TIME WE APCHED WHIDBEY ISLAND AIRSPACE WE WERE BTWN LAYERS WITH BUILDUPS. WHIDBEY ISLAND APCH INFORMED ME THAT WE HAD VIOLATED THE SEATTLE CLASS B AIRSPACE. I ASSUMED SEATTLE HAD CALLED THEM. WHIDBEY SAID THAT WAS A 'NO-NO.' OUR WX BRIEFING INDICATED THAT NANAIMO AND POWELL RIVER WERE VFR. WE SHOULD HAVE HAD SEATTLE FLT FOLLOWING AND THE CLASS B AIRSPACE WOULD NOT BE IN QUESTION AT THIS TIME.