Navpilot 500 with nervous heading sensor

[Buiz]

I used to be happy with the performance of my Navpilot 500 autopilot in my 100 ton trawler. I recently had to change my heading sensor (I now use this: https://www.svb24.com/en/digital-yacht-compass-sensor-hsc100.html). It transmits the heading to the Navpilot with 10hz and the technical installation is good.

On flat waters everything works well but with just a little bit of sea, the heading fluctuates a lot and jumps constantly 5-15 degrees back and forth as the vessel pitches and rolls. This causes the autopilot to fight the rudder to try to keep a steady direction against the constantly fluctuating heading data it receives. No amount of fiddling with the autopilot settings, especially the "weather" and "rudder gain" settings but also changing between the auto/self-learning and manual modes, sufficiently dampens the autopilot's furious rudder adjustments.

I'd actually be happy just using COG as the heading, which the Navpilot defaults to if I disconnect the heading sensor. However, until the ship has moved enough to actually generate a COG, without a heading sensor connected the Navpilot unit will issue a constant and incredibly annoying audible alarm for the missing heading data. This causes port manouvers to involve swearing and constant disabling of the alarm, which the Navpilot of course reacts to by restarting the alarm every 30 seconds or so.

Have I missed an important setting or other configuration parameter of the heading sensor setup or the autopilot itself? Any tips or advice? This can't be the first time a Navpilot installation has had to deal with "nervous" heading data.

 

[Johnny Electron]

No you haven't missed any setting. An autopilot can only be as good as the heading and the hydraulics. I note that this named unit appear to be a fluxgate type compass because they say it is for fiberglass/wood boats, but can be mounted outside for metal vessels. Normally when I have seen that done with any fluxgate, you have to get it up really high away from all that metal influence. I don't know if the heading is an issue because of that or just the device itself isn't great when it comes to pitching and rolling. I experienced a similar issue where a customer had attempted to use an existing compass (other brand than this one and not Furuno) on his new NAVpilot 300. Each time he accelerated and the bow came up, the compass heading would shift off 20 degrees and take a few minutes to come back on correct readings. He then decelerated and the compass would swing 20 degrees the other direction. It ruined the pilot. The heading source could not deal with the pitching of the boat. When you have a pilot it needs good data to work with. You give it bad data, it will not work properly. Last year I had a long term customer fit a SCX21 on his NAVpilot 500 and he loves it. I think your challenge is to get that device providing good data or replacing it with something that does. I personally don't recommend fluxgate units for any metal boat of any size. They are hard enough to deal with on fiberglass due to all the RF, motors, and large metal. I feel your pain. It sounds like you already had a pretty good idea what was going on. You are correct, that is the problem.