Crossing Straits of Juan de Fuca in 10 yard fog - we were in vessel traffic system east bound lanes - north of Pt Wilson. I had been using radar to track a fast moving target for many minutes. After doing several radar plots I kept seeing that the target and we were on a collision course - no matter how I changed our bearing and speed.

I made several blind calls on VHF 16 & 13 to 'eastbound traffic at location xyz' and 'eastbound traffic at lat x lon y' with no answer. VTS controllers reported no shipping in the vicinity. I made a turn to take Mirador at right angles to the targets course at 7.8 knots - still a collision course!

I had our fog horn sounding and continued to broadcast on VHF 16 & 13. When the target was within 45 seconds I brought our liferaft onto deck, and prepared to jump - but the target was huge so I didn't expect that the life raft would do much good.

Scariest moment I've ever experienced on a boat - Suddenly out of the fog came a solitary 3' high breaking wave - it was long enough I could not see either end. It rolled into Mirador, Mirador rolled 20 degrees side to side, I watched the radar as the target proceed past us, and all was well.

No idea where that single wave came from but it scared the crap out of me.