Measurements for Icharge - Forums Archive

Once and Future

2016-04-04 00:57:40

I got back to my boat and was able to do the voltage measurements that Icharge Al asked for. I have a 2,000mv range on my digital meter, which is equivalent to 2 volts. It read out in hundreds of millivolts, but I will move the decimal point here and give the readings in volts, as that is how most of us talk.

To review, the crux of Al's advice seem to be that it was important to simulate a fish near the gurdy wire with a snipped-off piece of gurdy wire. He wanted to measure voltage between the gurdy wire with the cannonball, and the snippet of gurdy wire, rather than to the rudder post like most of us do.

So, I got away from the harbor, lowered a cannonball to 13 fathoms. For my "fish" I took a 4 foot length of old gurdy wire, doubled it up twice, put an alligator clip with a voltmeter lead to it, and dangled it in the water.

1) Black box wire disconnected from gurdy, wire "fish" in water 2 feet from main gurdy wire, read +.69 volt on main gurdy wire with respect to "fish".

2) Same as above, except connected black box to gurdies, and left black box switch off: +.50 volts.

3) Same as #2, but turned black box on, and set to .5 milliamps: +.77 volts. (By the time I got back in the pilot house, milliamps on black box had crept up to .7 milliamps.

4) Measurement between main gurdy wire and rudder post with black box wire connected but box turned off (which is how I fished last year): +.55 volts.

5) Turned black box on with initial .5 milliamp setting: +.81 volts.

In summary, I think our old method of measurement is fine as a reference. Even if the voltage we measure isn't exactly what the fish feels, we can use it to be consistent. Apparently, the fish is going to feel about .25 volts less than we are measuring. And, there seem to be confusion over the polarity between the gurdy wire and the boat's bonding system, which is connected to the rudder post. My main gurdy wire was always a positive value with respect to my bonding system, and the ocean. Finally, Al asked me to measure the ohms between my gurdies and my rudder post. With the black box wire connected, it was 60 ohms. With the black box wire disconnected, it was infinitely high resistance.

Interesting to note that when I was dangling the "fish" in the water, the voltage reading remained the same whether I held it 1 foot from the gurdy wire, or reached it back as far as I could, 6' away.