Found this info from another site (Direct Copy Paste)
I finally found the report I mentioned in my post yesterday. It was actually a presentation by Bill Russell, a marine electronics expert from Victoria, that he gave to the Oregon Sea Grant Advisory Program on Dec. 16, 1975. Mr. Russell had worked closely with Canadian Salmon trollers for over 20 years about electrical and electronic problems. During that relationship he developed the concept and realization that "a trolling wire having a positive voltage will catch more fish than one with a neutral or negative voltage, especially during "scratch" fishing conditions". He stated that optimum voltage is between 0.3 and 0.7 volts positive with respect to the boats ground system. The trolling lines must be insulated from the boat and that the proper voltage field around the boat and lines can only occur if the vessel is properly bonded. He stressed that bonding is not grounding to the electrical system, but a separate circut not used to carry operating current.
He goes on to describe how to effectively bond together all the metal objects on your boat, both in contact with water and not and corrosion implications if not done correctly. His primary purpose in working with the trolling fleet was to try to develop methods to keep their boats from corroding out from under them and through that research the fleet catch numbers increased when certain conditions existed, i.e. the 0.3 to 0.7 positive volts.
Most of the descriptions and drawings in the report detail how to effectively create the bonding system in larger inboard boats, but the principal applies to every type of craft. I won't bore you with the technical process and drawings (if you interested, email me and I'll be glad to copy the whole report and send it your way), but suffice it to say he suggests a copper pipe bus and wires to EVERYTHING. He especially addresses the main shaft/outdrive and methods of accomplishing the task.
While trolling, the metal parts not connected to the bonding system (trolling cable and lead balls) set up an electrical field because of the dissimilar metals. That's what you're looking for. At this point he describes using a volt meter between the cables and bonding system to check if the cables are isolated (cables in the water about 6-8 feet). You want to see some voltage present. Also use the meter to check between each metal part and your bonding buss. There should be no current noted.
One intersting point he makes is that zincs just attached to a non-metal hull provide no corrosion protection until bonded to the metal part you want to protect. You can test your amount of protection you have by using your meter between the zinc and each metal device in the boat. The voltage should read 0 or no protection.
Once the bonding system is done then you check the actual voltage between the boat (bonding system) and wire; + to wire - to bonding circut. The voltage will be between 0-1 volt. As the voltages increased, catch rate increased until about .5 or .6 volts. Greater than that, the fish still hit, but were wilder trying to get them to the boat and more were lost. He felt voltage about +.5 the best. If for some reason the voltage was - fish would avoid the gear.
It's interesting that Cannon electrics used to use the water as their - pole (unit would shut off as the ball left the water) and actually created a - voltage environment. A good friend, that typically is very successful and has a great catch rate, bought a pair of Cannon electrics and noticed his very apparent decreased success. No offence to Cannon. I don't have any relationship to any downrigger manufacture, so no angry posts please. Only posing a question and personal observation. I don't know if Cannon still uses the same circutry. It was a couple of years ago. He added a Scotty Black Box that helped some. When he sold them on EBay and changed to a different brand he noted an increased trolling success. Go figure.
Anyway, another possible cause of a negative value is impure lead in the downrigger cannonball. Cannonballs cast from tire weights are notorious. It's suggested to check every cannonball on each wire with the meter or isolate them from the system with something like Scotty's plastic/nylon ball clip or use of a coated ball. A contaminated ball is typically the reason one side of the boat fishes better than the other, different voltages present. With the boat bonded, the wires isolated, and cannonballs checked, voltage should be +. If the voltage is low, more zincs can be added to increase the voltage, to a point. Attach the zinc to a wire that is bonded and lower it over the side. Check with the meter. Keep adding zincs until no further change is noted; probably +.5 or +.6 volts. Excessively high voltage may cause corrosion of the trolling wire, so just be aware. Not a bad thing, but may lead to the need to change downrigger cable. If you get a white powdery substance around a bonded metal fitting, it may be an indication of too much zinc.
All this said, this is the way you reach the desired voltage situation galvanically. A black box accomplishes basically the same result by placing that same +.5 to +.7 volts directly to the wire. Bonding is still a necessary process to acheive your desired result.
The unit I purchased on EBay for $5.50 plus shipping was called 'Electrocatch' by Scientific Fishing Systems. They were developed for and used by the commercial trolling fleet. The gentleman I purchased from was from Merlin, Oregon. His EMail in 6/2001 was email@example.com
. I don't really know if the adress is still current. He stated at that time that he had a bunch more of the units. The unit is completely sealed and waterproof and has a built in meter for output voltage(set at +.06 volts). For the money, it was an inexpensive lark and hasn't chased fish from the boat. If nothing more, after reading the report he included, it forced me to bond my boat.
By the way, typical disclaimer applies. My only connection ito him or the product is that I purchased one. Hope this was worth your time. Again, if you'd like a copy of the report, just let me know. Tight Lines.