Sorry to dredge up this old thread, but my electronics upgrade project has one or maybe two GMI 20 units for very similar applications. Would you please review the built in anchor drag alarm on the Garmin GMI 20 and how suitable it is to serve in this role beside one's bed as an alarm for anchor drag? Thanks, Ted.
For others who may be considering this, the first thing to consider is that you will need to leave the NEMA 2000 network on. On Slow Hand the network and the AIS were on the same breaker. The GMI 20 displays (3), all the sensors, and the AIS draw a very small amount of power.
The GMI 20 in the stateroom displayed time, depth, wind speed, and direction the bow was pointing (compass heading). Running but not displayed were anchor drag alarm and shallow water depth alarm. Other alarms are available such as wind speed, provided you have the corresponding sensors. The four items were displayed on one screen, so no scrolling was required. Other screens were setup so that I could manually scroll to see if things like maybe the wind direction had changed.
The display has a day and night mode, so you can set the night display to be readable but not bright enough to keep you awake.
Overall I was very happy with the display, but there are a few limitations. I don't remember if you link all the GMI 20s together or they come programed that way. As an example, if you switch to night time mode, they all switch and they all have the same night time light level. Somethings weren't linked. The most disappointing was the anchor drag alarm. You have to activate the alarm on the GMI 20 where you want it to alarm. So yes, I had the alarm ready to go, and would go down stairs to activate it, then come upstairs and drop the hook. The shallow water depth alarm would sound and display on all GMI 20s. I talked to customer support about updating the drag alarm on every display. They said it sounded like a very good idea and would be included in the next software update (software is updated where the oldest unit can have the same programming as a brand new unit. On my MFDs, it was done by running a software update in the SD card slot where SD map cards were inserted). I became so use to trotting up and down to the stateroom, that I never bothered to update the software.
While there are other apps that you can use on a cell phone or tablet with far more features, there are some distinct advantages to a GMI 20 in the stateroom. First, the GPS antenna located on the top of your roof is probably multiples better with a faster sampling rate and unobstructed view, than what's in your phone or tablet. Secondly, all the other information and alarms allow a more informed decision of whether you need to get out of bed in the middle of the night. Third, being able to wake up and look at it with the same informational display, same light level, in the exact same location, without activating the screen or trying to display the app correctly is extremely valuable.
If you can now activate the anchor drag alarm from the pilothouse and have it alarm in the stateroom display, that would be perfect!
Ted