I was having a chat with a chap yersterday who was having a nosey at my boat and fishfinder. He was telling me that by using the GPS as a source of reading speed when trolling would not give an accurate reading as it was ground speed and did not take account of the water, flow etc due to the wind

I had a look on the web and some guys agree. I wonder though is this is for when you are trolling on a river with a current???? I am not sure about if you are on a loch. Does the wind, wave etc make any difference to the GPS Ground Speed?????

What do you all think - GPS is the most accurate speed sensor apart from the Lhur Jenson speed sensor??

I started off with the Luhr Jensen speedo and when i got GPS for the boat i found that they were running more or less identical,so i think the gps is pretty accurate, there might be water speed issues with currents etc but i think they will be so small as not to worry about.

If you had tons of money and a big enough boat you could get a fishhawk speed probe where you have a paddle wheel at the surface and one that attaches to the cannonball and that will give you surface speed as wel as lure speed and temp at the depth you are running at, they are about $700 and the probes are around $200 and have been known to drop off in to the drink .

Another goodway to judge your speed is to look at your downrigger cables to see the angle they are running at, i use that method often a quick check at the GPS then tells me if i am going to fast or too slow my prefered speeds are 2.2 to 2.8 mph

Feroxhunter - someone is playing tricks with your mind!! I think the only important measure of speed is actual ground speed. Thereafter, you can take any other elements, weather, wind, tide, stream, current into account and adjust your speed to suit your particular style of trolling or lure you're using. If your GPS/fishfinder/chartplotter offers various set-up settings (such as 2D, 3D, WAAS), then set it to WAAS for the greatest accuracy both as to position and speed over ground.

In reality, speed is simply a measure of time over a measured distance. If you really felt that there was a noticable/significant variation between your Luhr Jensen speedo and your gps, which frankly I doubt, then you'd need to more accurately calibrate the log error. No speed log as a measure of speed through the water can be expected to be 100% accurate, as the boat may drag some water along with it, making the water flow past its transducer/impeller/paddlewheel slightly less than than the boat's speed through the water, or the impeller/paddlewheel might not be spinning freely. Alternately, the water flow may be accelerated as it passes the keel or is sucked into the propellor, to make the log overrread. Calibration of any error variance of your gps reading of speed over ground versus your water log speed is of no real relevance to you as a trolling fisherman unless you're trolling from a supertanker!!

Absolutely - sit back, relax and prepare for the big strike!