[Capt. Lou]

I've used downdiggers for over thirty seasons on local water & my charter on Lk. O for over 15 seasons.
The old Invader alligator clip style worked for light yo medium duty, I believe Yellow Bird , offshore & host of others offer this style.
Light lines like used locally used the med weight release pressure!
Invader called this their Walleye release.
Use the heaviest weight your rigger will allow! Try to obtain a slim weight , this will cut water better & lessen scope when down deep.
The above mentioned set will allow for stacking a method that allows you to add more lures through the complete span of the thermocline!
The noted releases will work as stackers as well .
Speed is always ascertained by lure action , maintain a log book & note best speeds for various lures.
This can change with wind , depth trilled etc.' Deep water generally over 50' or so the scope factor if around 10% off lure depth,so your DR gauge would read 55'
to troll this depth.
If you have electronics , GPS will post your speed , however this will differ at the ball for various depths!
I used a electronic device to ascertain speed & temp at ball!
In local waters your main concern is a good topo map & down temp gauge , using these you can catch as well as anyone with an ff!
Rigging locally keep everything light, lengthen patterns from weight, experiment to you develop a technique.
you can PM me if you have Q's !
PS I personally never cared for DR's in local waters always used other methods to troll deep.
Good luck!