The ideal system has an earth stabilised sensor! Who makes those?
What price?


Not sure if this is really earth stabilized (like an INS) but KVH made
something a few years ago called a Digital Gyrocompass, had inclinometers, rate
gyro accelerometers and a flux gate. Cost several K. No longer made, but they
show up on eBay from time to time, usually for under $400. Has NMEA heading
outputs and also synthetic gyro stepper outputs. KVH's Gyrotrac was the
successor product but they are junk according to several commercial tuna
fishermen who smashed theirs and sent the pieces to KVH after KVH refused to
support them post warranty. They ALL failed within a year after warranty
expiration. Worked GREAT until failure, rock steady accurate heading no matter
what the ship was doing in the other axes, but not a long lasting product.