Rope length is relative to the water depth you are fishing, I use 25 foot of rope but rarely fish in water over 20 foot deep.
Chain size is also relative to boat size, you boat a couple of 5 foot lengths od 3/8 should do the trick.
Main thing is to be able to pull it pretty easy without having to ramp the troller up too hi. I have 2 lengths of 3/8s 8 foot long, 2 5 foot pieces and 1 5 foot length of 1/4 inch in my box and mix and match depending on the situation. In the tourney Saturday I had 1 rope with an 8 foot length of 3/8s on it and the other with 13 foot of the same chain on it, that's what it take to stop the Bass Cat in 20 foot of water. Had I had more rope on them it would not have taken as much but the ropes were almost straight down so less leverage.
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