Feet of water question

To use your example, 57 fow is the water depth reading on your fish finder.  The fish could be anywhere within this water column, from hugging the bottom to a few feet below the surface.  Fish finders mark the depth of the fish as they swim thru so you can target them accordingly.  Will you be drifting?  Casting?  Trolling?  I've always heard walleye attack up, so you probably want to get the lure in front of them or slightly above.  We used to fish for northerns off Manatoulin Island in the Georgian Bay.  Beautiful up there.

Drifting or anchored will be the easiest way to fish, but not always the most productive.  There are a ton of calculations when trolling, special equipment is almost necessary to troll properly in that deep of water (whether it is lead core, dipsy divers or down riggers).  You might get lucky and have a lure that works well.  There are charts online for many trolling depths of lures too.  They will tell you how far a lure will dive, going a certain speed and a certain amount of line out.  You can add trolling sinkers or bottom bouncer weights to help you out too.  In 60 FOW, bottom bouncers will have to be very large, and a lot of line out, to keep contact with the bottom.
 
Marking fish is one thing.  Usually better to mark baitfish (usually a blob on your fish finder), with fish under them.  Find the depth of those baitfish, and try fishing there.  If fishing in 60FOW, with fish suspending at 30FOW and baitfish at 25FOW, then try to get your bait around 25FOW, but vary it from 20'-30'.  Using a 1/2oz - 2oz trolling weight or carolina rig (or blade bait or jigging lure) will get your bait down deep, and should keep it rather straight down from your boat.  Before you go out, measure from the spool of your reel, to your first eyelet.  Find how far that is, usually around 2'.  If not 2', but 2' is another 3"-4" down the pole, either put a mark on your rod or remember where 2' is.  If you want your bait at 25', get the sinker at the water level, without just letting it sink and guess, pull out line from your reel and count by twos.  This will put you relatively close.  If fishing two rods, do one at 10 pulls of line and another at 12 pulls.  If no bites, try different pulls, until you get some fish pulling...  Remember and repeat which one is working best.  If there is a decent drift, you will have to pull out more line to get you to that desired depth.  Often times, your fish finder will mark your lure/bait too.
 
For $10, the link that Crawlerman referenced, you can load maps on your phone, and use as GPS on the lake.  I think this uses data, so would only recommend if you have an unlimited plan.  You may want to find all of that out before ordering.  If it works, mark waypoints where you get strikes or catch fish.  That way, when you are out there, and get 2-3 bites in an area, you can get right back to that area and not try to guess.  As you know from shore fishing, often a foot or two difference in a cast is the difference between limiting out and getting skunked.