Let's just get this out of the way: Fat Bikers want to be biking. The primary goal of this article is to get you back on your bike. The more effective you are in packing a trail the quicker you'll be done with all of this snowshoeing stuff.
NOTE: this is a guide to grooming trails right after a big snowfall. Once packed and frozen the trails are open for all to use: bikers, skiers, runners, and hikers.
With that in mind, here is the most important goal:
Follow the same line you ride all year long. Pack as if you are on your bike riding the line: don't go around fallen branches, clean them up. Each pass you make with snowshoes you should be packing and reinforcing the center of this line.
In the illustrations the line is represented by a fat tire track.
This is a snowshoeing pattern. This does not pack the line. Do not snowshoe.
Instead, use your snowshoes to pack.
That is packing! Half steps, snowshoes close together ... stomp if you've got the energy.
"Oh, man, that's going to take forever!" you groan.
It is slower, but you are accomplishing the goal and getting closer to riding again. We're going for quality, not quantity. Trust me, it's much better to have a few miles of rideable trail than miles and miles of crap no one can ride. If you have to waste time on snowshoes make it count!
For the second pass we offset the packing pattern 3-4 inches to the left or right. You'll see a ridge of snow down the middle of the trail from the first pass, which this pass will pack down nicely.
It's tempting to go way off to one side or the other and really widen the trail, but that's not packing the line. Remember:
Snowshoes range from 8 to 10 inches wide. After your first pass the trail is going to be 16 to 20 inches wide. When you offset four inches your inside foot will be packing the line while the outside foot is widening the path, which will now be 20-24" wide.
Note: this second "pass" could be a second person in the packing party.
Now we're talking! In the second pass we offset 4 inches to the right. The third pass offsets the other direction. Most importantly our center line is 8-10" wide and has been packed three times. There's a 20 inch swath that's been packed twice, while the very outer edges (3-4") have been packed once. The trails is well over two feet wide.
How much packing you need completely depends on the depth and nature of the snow. This winter we've been getting 6-8" of extremely powdery snow with temperatures well below freezing. It's taken 4-6 passes to get a rideable trail after some of the storms. If there's less snow or a wet snow then maybe only 1-3 passes are needed. If you need more than 3 passes just repeat the left/right offset outlined above for the 2nd and 3rd pass, widening out a bit if needed, but always packing the center line.
If the trail needs more packing just remember to always have your inner snowshoe packing the line. The reasoning for this approach is that it not only strengthens the line's packed snow, but also reinforces it visually. Visually because the next person who comes along packing (or riding a fat bike!) should be able to see where the line is.
That's a nice wide trail! But where's the line? If you've got a big enough group (or enough time for extra passes) then this might be a good starting point, but the trouble is that it will take a lot of passes before all of it is rideable. And if you don't pack all of it no one knows which parts are packed and which parts are going to swallow their tire. Much better to start with a well packed, narrow trail and work your way wider when you have the time.