Leadcore line is viewed as the simplest method to troll deeper.
The leadcore is a simple line while bigger than others, in which the core is made of lead, or replacement, coated with a nylon outer. The outside nylon change in color every 10 yards. There are 3, 5 and 8 colors lines. There are also many breaking strength from 25 lbs and going up.
The calculation is somehow the simplest: run your boat at 2 knots and for each color the line will go down 5 feet. Or maybe it goes 4 feet. Or you are fishing in salted water and your boat doesn't really goes at the sentenced 2 knots. More, some of your buddies will say 2 knots, while others say 2 mph. It's 10% faster.
So you agree with me: 3 colors will bring your lures "roughly" at 15 '.
By the way, 2 mph is the perfect boat speed to fish stripped bass ... between June 15th and June 21st.
I'm joking but you agree with me the trolling speed is a feeling. You feel the right speed and it depends of many parameters. With DipsyTroller, adjust the speed with the slider and you'll have the true amount of line to let out.
I'm not either a mad scientist! I know that one feet up or one feet down will make a big difference in your catch rate but if you're fishing the Great Lakes at 50' in lieu of 60' it certainly make a difference.
I don't like leadcore line it's easy but you need to have one rod dedicated to it or at least one reel. Then you can't do anything else with it. I really prefer a rig for Dipsy which can be use with other divers and which need a lot less of line out to reach the right depth. The other situation where the leadcore line is bulky is when you want to use planers. You need to let out the leader, the full leadcore line and some for the planer. If you have a strike, you have to bring back, at least, 200' of line. What a dumb chore!
The other problem with leadcore line is that the knots are bulky and while I have a solution for that, I'm always fearing that I'll lost a fish because of them.
Leadcore leaner knots
Turn the lead core line several times near the end, breaking the lead inside. Pull this lead out, and you will be left with a small length of the nylon outer coating which you will tie to the "backing," the monofilament fishing line already in your reel.
Break the lead at the other end of the length of lead core line in the same manner. Again, pull the broken piece out and tie a leader to the empty nylon. The leader will carry your lure, and/or bait and hook.