Yes you can run a Planer on your Downrigger - I run # 4, 6 & 8 - because that the largest I own ........
# 1, 2 & 3 run from the rod or parachute cord hand line .......
Been on boats that run large Planers # 16, 24 & 32 on 90 to 125 feet of 300 # mono with a rubber band & large paper clip release to the fishing line ........
Hope this helps ....... ICM
Florida Sportsman Mag. has 3 video on Downriggers & Planers .......
http://link.brightcove.com/services/...tid=1344510684