Re: Navigation Problem
"recording the tidal speed when racing on a log - say every 1 minute preferably using a smart phone "
Not so simple. If you want tidal current information (tides are vertical, currents are horizontal, tidal currents are the horizontal movements caused by tide changes) you will need speed through the water, as measured by a knotmeter on the hull, plus speed over ground, which is the only number a smartphone with gps can give you.
So you're going to need instruments on the boat, not just software, to generate that information. I'd be surprised if the final price was attractive.