Going off course, does 66i auto reroute?

I assume you created a Course on Explore, synced it to the 66i and then followed that Course on the 66i? If so it could be due to difference in the maps that are on the 66i and the maps used by Explore.

First to explain the difference in various navigation options. The unit supports Tracks (Activities), Routes and Courses. Tracks are simply breadcrumb trails, without any navigation features. Routes are collections of points and the unit calculates a path between these points using the map active on the device. Courses are kind of a combination of Tracks and Routes: they contain the path you plotted and also allow for navigation when you deviate. See https://support.garmin.com/en-US/?faq=uJZh4J9rF20RVCRNfCtXV9 for the official Garmin explanation.

When you create a Route in Explore and sync it with the unit, the path calculated on the device may differ from the path in Explore. This is because the unit will recalculate a path between the route points based on the active map and routing settings on the device. If you follow the route, you will get turn-by-turn instructions.

When you create a Course and sync it, you basically have two options on the GPSMAP: either follow the path as is (Direct routing), or use the roads and trails of the active map (Roads & Trails routing). In the former you won't get any turn-by-turn instructions. In the latter you will get those instructions. See https://www8.garmin.com/manuals/webhelp/gpsmap66s_st/EN-US/GUID-89CA1585-37F5-414B-8A47-8499C9C59D0D.html

Personally, I use a workflow where I create a path on a 3rd party site (Komoot mostly). This gets synced to my GPSMAP as a Route from Komoot via Garmin Connect. Then I either use Direct routing or Roads&Trails routing depending on whether I want instructions or not. If I want to plot something on the go, I use Explore and create a Course that I sync to the device.

Hi Like2Hike 

The flags shown were added purely to show the direction that the 66i suddenly decided I should go. 

The actual direction of walking I had planned is the white line to the north of the quarry. 

I don't understand why the 66i "rerouted" rather than warning me I was off course. (The marine off course warning was on)

It's a bit like Google maps that automatically reroutes once a wrong turn is taken. But in this case it entirely missed out the remaining half of the hike and sent me back to the beginning via the quickest route. (I wish Garmin did not use such terminology that is easily confused with its literal English meanings, would make life a lot easier) 

So I am trying to understand why the redirection occured and what if anything I do to prevent it occuring again. 

Any ideas? 

I don't see "quarry" on the map. I see the white line which seems to be part of a loop trail, with part of the loop not shown (to the left or west). I see the flags, but I don't know if you're traveling north to south or vice versa. Sorry.

As a hiker, I don't use the Course or the Route Planners. Courses are best suited for fitness routines and Routes are best suited for automobile-like applications. Most people involved with fitness programs do them close to home, they don't even need GPS. Unless you are biking/hiking/jogging into a new town and you want to know where the closest restaurant/hospital/hotel/etc. is the Route Planner doesn't have much value to me.

I just use Tracks because I'm on trails. If you pre-load a Track into Saved Tracks and then select that Track when you want to hike, it will give you off course (& back on course) notifications. (They really should be "off track" and "back on track" notifications, since courses are specifically different).

I don't want to be hiking and have my GPS constantly beeping with numerous instructions. That's annoying and unnecessary. I follow the trail itself and on occasion where I'm uncertain about something, I'll consult the Map on the GPS.

I don't use the Explore app for navigation because it just depletes the phone and 66i batteries faster than not using it. I would use it if I could foresee doing a lot of custom texts. It's faster to type texts on the phone than on the 66i. Once done, I would turn off the Bluetooth on both devices.

Sorry I can't be of greater assistance.

Where I am hiking at the moment there are literally hundreds of different ways to reach the same point, there's firetrails, mountain bike trails and walking tracks criss crossing everywhere. I like to plan a route that uses all 3 to be a little more challenging, so the directions are vital, as getting lost in the Australian bush is often a death sentence. 

You have been helpful because as we both agree, the terminology Garmin uses is confusing and doesn't match normal everyday usage as to meaning. Similarly there is little explanation of how all the various apps, maps, and devices integrate or even if they do. 

I am sure I will settle on the best way for me, but it's certainly challenging. I would rather be hiking or kayaking & bush camping. 

Have a great day 

What I would do under the circumstance you describe, is first go to a community website (like AllTrails, HikingProject, etc.) and find as many of the potential trails as I could and download them. Import into the Explore Website as Tracks. Then synch to the 66i. As long as there is at least one, I know I can reach my destination and it will be on the Map. (Either because it is actually on the 66i Map or I would create a Waypoint upon reaching the destination).

After hiking some of the downloaded trails, I would ensure I am using my Recording Controls and try something adventerous.. On the Map, I would know where I am, where the destination is, and see some of the downloaded trails as backup egress paths. Then set off on a novel hike. I would have Track Back available to take me back to my starting point if I couldn't find a way to reach the destination. But with "literally hundreds of different ways", I would be fairly confident I'd make it. If I reach the destination, I would save the recording to use as a reference in the future. (If I was particularly concerned about getting lost I would also use inReach Tracking and MapShare.)

Have a great day, too.

I wouldn't be relying on routing directions in those situations either. Onboard map content varies and often doesn't even include or match tracks on the ground and at best will be out of date. As you have discovered it's a good way to do your head in and create the very problem you want to avoid.

Also agree keeping an eye on tracks or a waypoint is a better option with your primary awareness on the bigger picture of the terrain and where you are in it and where you want to go.

There are also other more detailed maps available that can help you better understand that in Oz. The full version Garmin Topo Aust & NZ is good, and also our local OzTopo product. I use both and rarely the onboard Topo Active but, in some places even that includes detail the others don't. These cost more but I think they are worth it.

The general advice is work on your basic navigation skills, one day your battery is going to go flat.