I was on a cruise last week in the Caribbean and brought along my Garminfone. The GPS function worked well while in ports, but during some days at sea it would give very erratic readings. I assumed that the probelm was we had travled a ways from the last readins and were moving at about 20 + miles per hour. However, there were a couple of days where it never did give a correct reading. Any thought?
Well, given the limited data in the posting, I would suggest reproducing the experiment, but bring along another known good working device with the appropriate maps. If the other device works correctly and the test device does not then you can make a conclusion.
Otherwise there are too many other variables and not enough data to constrain the problem.
In my experience, it is harder to get a lock while moving. This would be compounded by the fact that you had "travled a ways from the last readins." Smartphones may have a poorer antenna than dedicated units and rely more on A-GPS, further compounding this issue.