Maybe we need to go with 12s instead, the ones were using have rudders on them and don't seem like they weigh very much. I found this conversion chart to help out:

http://www.lakemichiganangler.com/tips/downrigger_depth.htm

I bet we're fishing at 50 - 65 ft in reality, because most of the time we've got our rigger cables out to 70-85 ft at a 45 degree angle. Just seems like sometimes were going way too fast, but then we watch other folks nail them going faster then us.

Oh yeah my 13 come from the little residents we were catching before the main run came in.