Gary, I have a quick question. When I bought my boat, the heading sensor was mounted at the dealer just in front of the console. Would moving it to the bow of the boat increase the performance of the Ultrex? I have no problems in open water but it goes crazy under bridges. I assumed and was told that I just would not be able to get a good GPS lock under the bridge. Thanks for any input you might have.
The heading sensor is a COMPASS. I'm fairly certain there is no antenna in it. (The GPS antenna is in the TM head, not that this would matter to what your actual issue is.) People get confused because the heading sensor is in the same type enclosure as GPS antennas. The reason you (and anyone else) has issues around bridges is STEEL. Think of the massive amount of rebar steel in that bridge, including the pilings. Now, think of how much that will likely confuse a magnetic sensor, aka, compass. Moving it won't make any difference. As far as heading change goes, if the bow makes a heading change, the rest of the boat makes the same change. The dealer was actually doing a good thing to get the sensor away from all the electromagnetic energy that is typically in the bow area.
I guess I should clarify that your TM still uses it's GPS antenna to spot lock. It uses the heading sensor to determine whether to adjust by turning the TM left or right. Besides the bridge typically messing with compass stability, a bridge above will block a significant part of the sky view typically needed to calculate position and adjustment vectors.