Speed/Temp Probe question

[bowbender]

I just got a Subtroll this year and used it for the first time last weekend, and I have a question. I trolled all directions experimenting with it trying to see if I could figure out the current direction. Any direction I trolled it seemed my GPS registered 0.5 - 0.7 mph faster than the probe, I had to go 3.1 SOG to get 2.5 at the ball. I don't have a problem with that except it seems that against the current the speed at the ball should be faster and with the current it should be slower. I was fishing out of Holland and predominantly trolling SW & NE. According to the NOAA current charts I thought I would have a ball speed faster going south and slower going north. Am I doing something wrong, looking at it wrong, or do I just need to adjust the speed on the Subtroll to match the GPS were I know there is no current?

[Dr Hook]

GPS and probe speeds are usually out of sync and calibrated differently. A better way to tell current is to look only at down speed. Watch your down speed and start to turn slowly. If down speed starts to drop your turning to run with current. If down speed increases your turning into current. Changes are usually small, only a few tenths. If the difference between GPS and down only changed from 0.5 to 0.7, that may have been due to current.

[bowbender]

Wouldn't GPS speed be most accurate? Should I adjust my probe to read the same as my GPS when I'm in a shallow no current area? Were my baits moving at an effective 2.5 or 3.1 mph? Sorry about so many questions but this just raises more of them. just restarted Great Lakes fishing again after a 25 year hiatus.

[highpointdf]

Ideally yes you should set the probe to match the more accurate gps speed. From that pout you will be better off knowing your speed at the ball

[SeaCatMich]

GPS SOG is measuring your boat's speed over a specific distance as measured by calculating the difference in LAT/LON positions between signal pulses from the GPS satellites. Down-speed is measuring the speed of the probe/ball/lure relative to any current in the water. Basically as far as attempting to duplicating a lure's speed when it gets hit, down-speed is the important one. I don't really even look at the SOG when I'm trolling -- when I'm cruising, yes; trolling no.

Are my lures actually going the mph that the FishHawk X4 says? I doubt it. Is the number shown repeatable and showing me a relative measurement that I am going to use to make my lures have the same action that caught the last two fish? I am going to assume it does since that is why I bought it.

I have two different GPS units on my boat. They give me different speeds because the algorithms used for calculations by the different companies are different. Add in my boat's speedometer, the fishfinder transducer's paddle wheel, and then my FishHawk's surface speed and on my boat I can have 5 different speeds being shown that all claim to be the "accurate speed" of the boat.

On my car the GPS speed is often different from what the car's speedometer says and it is different than what the radar timed speed on the "you're speed is" signs says the car is going.

[jdh]

As highpointdf said - matching speeds are ideal. After you get that though, you still need to figure out what speeds work best on your boat with certain lures.

[Far Beyond Driven]

My sub troll is always lower than my g p s. Whatever. 2.0 on the subtroll for lakers and kings, faster for steel.

As said above its about repeating the value, not the value. Find your numbers and go from there.

[bowbender]

Thanks everyone for all the input, as usual you guys are great, I've learned so much from everyone on this site, I just have to get out more and put it into practice. I am going to use the Subtroll predominantly for repeatability as everyone has said. It was just the first time using it and I was expecting a little more change between the two systems when I went in different directions, showing the currents. It does kind of bug me though to have the Subtroll read different from the GPS. I may check it at the surface in a no current area and tweak it to read the same as the GPS if they are different.

[bfr]

I think that's a good idea. Your understanding of up-current and down-current speed variation and comparing it to GPS SOG I believe is spot on. The reason many boats show so many different "speeds" is often just that their operators never took the time to tweak the calibrations that many of the systems are capable of. Same could also be said for many boats "depth" reading. Would love to know how it works out for you after you've got it dialed in.

[bowbender]

Calibrated the Subtroll tonight. It was about 0.5 to 0.6 mph below the more accurate GPS speed, went all different directions before adjusting. In the famous words of Marisa Tomei it's "balls on accurate" from 1 to 3.1 mph�� (pretty good analogy for a cannonball down speed probe hey), above there it's about .2 off. I think this will help me figure currents better. Thanks everyone for the help.