The most common diver out there is the Luhr Jensen Dipsy Diver.  There is also Walker's Deeper Diver, new in 2007, which is very similar in operation to the Luhr Jensen, and some others.

Purpose

The purpose of the diver is to get your bait deep and it can also be use to get your line out away from the boat.  If you are starting out and have no Salmon trolling equipment at all, you can start out with a couple of divers.

What you need

Rods

• You need a stout rod, usually a fairly long one, to get the line away from your downriggers.  Most Diver Rods are 9-10 1/2 feet long.  The exception to this is sometimes two diver rods are used on the same side of the boat, do the "deep" diver rod can be shorter.  the Heartland Diver Rods are what I use on my boat.

Reels

• A line counter reel is a must.  Without a line counter, you can "count passes" on the reel, but if you are like me you will forget how many you have out.  The Daiwa 47LCA is a good size reel for this use, as is the Accudepth Plus 47LC

Line

• You can start out with 30 lb Mono line.  Mono is good for a beginner as it has some stretch and is "forgiving".  If you have a lot of line out, releasing a diver (more on that later) can be difficult.
• You can use a braided line like the Power Pro 30 lb.  This line is "no stretch" so you feel every bump, and there fore it is easier to release.  The advantage over mono is the thin diameter means you can achieve much deeper depths than with mono.
• You can use wire line.  Wire is like braid except many believe the wire catches more fish.  I believe that on some days it does.  Wire is definitely not a "beginner" method.  Wire line is expensive, wire will cut through other lines and your hand, and wire line in your prop is a tow-home situation.  Wire lines will be discussed elsewhere.
• My divers are all braid or wire.  You can use a braid diver as a "high" diver but you cannot use a mono diver as a low diver.  I simply do not need two more rods on my boat.

Snubbers

• There is some debate over snubbers.  I firmly believe that they are necessary, some do not.  Some people have even blamed losing fish on the snubber.  The fact is, sometimes you lose fish.  If the hooks are sharp and you are keeping the rod tip up, it's just the way it is.  I always use Opti-Snubbers
• There are several types of snubbers out there.  Luhr-Jensen types are Dacron sheaths with a cord in the middle.  there are others that a surgical tubing with line in the middle.  Basically the idea is that there is some benefit to limiting the stretch of the snubber with a cord.  I don't know what that benefit is.  I use the Opti-Snubber which is basically a big, heavy rubber band.  I stretched one out 5 feet once with some weight lifting weights in my garage, and left it stretched for a couple of months.  It never broke.
• Opti-Tackle makes a black and a clear snubber.  The clear ones turn brown in the sun after a while.  I have not noticed any problem with the brown, but it bothers some people.  If it bothers you, buy the black.  I use the clear.

Swivels

• At the end of my line I use a heavy ball bearing 4x6 120# Swivel.  On my leaders, I use 2 75# 3x3 ball bearing swivels.  You can have $30 worth of equipment at the end of your rig, don't use cheap swivels.

Leaders

• I use ANDE Monofilament for my leaders.  Some people use fluorocarbon for their leaders, I don't think it is necessary.  If you think it catches you more fish, go for it.  Running spoons it might, running attractors and flies I doubt it.  With spoons you can use light line if you want and a smaller swivel on your leader on the spoon end, but with attractors and flies I just use 30# ANDE.

Leader length

• Generally, for hooking fish, the longer the leader the better.  For landing fish, a leader over 10 feet can be a real pain in the neck.  If you have a 13" flasher and a bait rig, I use a 6 foot leader.  Small flasher/dodger and a fly I use a 8 foot leader and for spoons I use a 10 foot leader.

Rod Holders

• You need a good rod holder that adjusts from Horizontal to at least 45 degrees up.  The lowest or single diver on each side of my boat is straight out over the water.
• The diver rod holder should be positioned well forward of the downriggers.
• The rod holder should be mounted well and reinforced.  If the rod holder breaks off, that can be $200 plus the cost of repairing the boat.
• Bert's Ratcheting Rod Holders will ratchet up as you pull on the rod, so you don't have to lean out over the water to pull the rod out of the holder.  This can be a big deal in rough weather and a big fish.

The line attaches to the release that snaps in and out of the top of the diver.  You need a leader from the diver to the bait.  In between the leader and the diver I always use a snubber.  You can run any bait/lure/rig that you can run on a downrigger off of a diver.

First, decide if this is a "high" diver or a "low" diver.  If fish are in the top 50 feet of water, dial the weight to "3".  Below 50 feet, dial it to 1.  You must keep in mind where your downrigger bait is when setting out a low diver.  Next, set the release.  The wire should snap in and out of the release easily, but not too easily.  (That's probably the least helpful thing you will ever read.)  The only thing I can tell you is, experiment.  If you are getting false releases, tighten up a little bit.  If you go too far, it will not release with a fish.  You will think you have a 40 pound fish on the line and you will most likely lose it.

I like to run the diver straight out the back of the boat, which is clear of lines.  When there is little tension on the line the diver will not pull to the side or down.  When I have some line out, I tighten the line and guide the diver around my riggers and into place.  Do not let the line "free spool". 

Use your depth chart that came with the diver, or the Precision Angling books to get above the depth you want.  I like to set my divers and then periodically let out 5 feet of line until I get hits.

When a fish hits and the diver releases, the line will go slack.  The longer the line is slack, the more chance of losing it.  Get right on that rod and start reeling until you find the fish.

Bob's #1 Rule of Salmon Fishing - When in doubt REEL!  It hurts nothing to reel in a false release, but many fish are lost when the fisherman thinks that the fish is gone and stops reeling and the fish is charging the back of the boat.  Steelhead/Rainbows do this a LOT, as will Spring Kings.