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Brian Boschma, a man of many talents, a short handed sailor and all around good guy thinks outside the box. And sometimes outside the boat. For instance this little gem on something most of us would never think about. However if you are navigating in dense fog, and are counting on your compass to get you safely through the narrow passage under the eastern span of the new Bay Bridge, you might be surprised to learn what Brian has discovered...
~Brian Boschma~
The new Bay Bridge stanchions, on the NE side of the bridge exhibit a substantial magnetic anomaly. In two recent passes through the bridge I have measured shifts of over 30 degrees when passing under the bridge and within a few boat lengths, approximately 80 feet, of the stanchions. The anomaly is most pronounced near the center of the road bed above you. If you are steering by autopilot this anomaly can lead to a collision with the piers.
I happened to be testing an AP on Apr 11 and opted to engage to see the effect. As you approached the piers from the north the AP would attempt to alter the course significantly towards the east. Traveling from south to north and with the piers within a few boat lengths would have certainly resulted in a collision. My measurements were to the east of the E pier, this is outside the new construction zone (the area with scaffolding, between E and Yerba Buena, is restricted).
I then made another pass paying close attention to a flux gate compass with heavy damping, while moving at about 3 kts. The shift was apparent in the readings. The old piers, to the south, showed no such disturbance. I pass this along as a safety tip. I already know of one boat that mysteriously hit the new construction when an AP made an unplanned abrupt turn.
I happened to be testing an AP on Apr 11 and opted to engage to see the effect. As you approached the piers from the north the AP would attempt to alter the course significantly towards the east. Traveling from south to north and with the piers within a few boat lengths would have certainly resulted in a collision. My measurements were to the east of the E pier, this is outside the new construction zone (the area with scaffolding, between E and Yerba Buena, is restricted).
I then made another pass paying close attention to a flux gate compass with heavy damping, while moving at about 3 kts. The shift was apparent in the readings. The old piers, to the south, showed no such disturbance. I pass this along as a safety tip. I already know of one boat that mysteriously hit the new construction when an AP made an unplanned abrupt turn.
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