Well, this post prompted me to sign up to this site so I could reply. How deep are you trying to get? I often fish in over 100fow with 12 pounders with acceptable blowback. 14#ers work even better if I'm trying to contact bottom.
It's a great idea, but it seems it does a few things wrong to make it worth while. First of all, aren't you actually decreasing the life of your riggers by making them pull up twice as much cable every time?
Also, now you have to have twice as much cable on your rigger to get to deep depths. Most riggers don't have more than 400, so now you're only getting down to less than 200, and I can bounce bottom in 200 or deeper with a 17# Shark weight if I control my speed correctly.
Another thing is having 2 cables in the water will surely cause more blowback, not to mention the increased chance for a tangle if a fish makes a crazy charge when he sees the net coming.
Quite frankly, I wouldn't pull weights that heavy. The shape of the weight is more important. I've witnessed a 25# round weight with a small fin pull back considerably farther than the 17# Shark did. And that was with over 200 foot of cable out. We've also bounced bottom in 300 fow with that same weight by slowing down at the right times and letting the ball drop. Caught some real nice Lakers doing this, as well as a couple Kings.
I have to commend you for pioneering an idea to fulfill a need, but it seems that you are taking away from what you are trying to accomplish by doubling your cable in the water, plus a pulley creating even more blowback. There are guys that fished crazy deep for big Kings and they had special riggers built to accomplish the task. Imagine sending 1000 feet of cable out to get 400 foot deep?!