I have a smart phone (Samsung S4) but I often fish out of cell reception so it isn't much use.
GordJ, thanks good info in that response. Everything you said makes sense. The last thing I am wondering is when guys are fishing in the ocean etc, going with/against the tide and so on, how do they know how fast their gear is moving? I doubt they have something like the dinky Luhr Jensen trolling speed do-dad that drags in the water.
If this can't be measured by GPS or sonar, how do they know how fast they're moving over water? I was watching fishing show the othe day and they were trolling for kokanee. The host was talking about dialing in trolling speed and said he likes to troll between speed A and B. I forget what is was say 2.3-2.5 mph or something like that.
If one is going with/againt the current how are you to know how "fast" your gear is moving? IMO rod bend would be a realistic guess, however if fishing downriggers it would be harder to tell as the rod always has a good bend in it.