I use a Maretron SSC200 rate gyro compass on my steel
boat, and it is located in the pod above the companionway
. A hand-bearing hockey puck
swings through 35 degrees when moving through that gap, so I was more than a little skeptical... but the process worked perfectly (taking the boat through three full 360 degree turns at a fixed rate while running a utility on the display). It now agrees precisely with the professionally-tweaked binnacle compass, and I like it a lot better than flux gates.
I was running my GPS
datalogger during the calibration, by the way, and didn't realize there was a current
running on the mirror-smooth waters in south Puget Sound
... made an amusing image.