When I row, I generally have both my iphone running CrewNerd and a Speedcoach XL2 in the boat. I bring the phone because it is a reasonably lonely stretch of river and it is a recommended safety accessory. Since I need to have it in the boat, I might as well have it do something useful.
I have used both CrewNerd and Rowing In Motion and there are pros and cons of both. RIM is a great tool for real time feedback in the boat. CrewNerd has better data export features and good tools to review a workout on the phone including a map view and nifty graphs of pace, rate, HR and stuff.
The major disadvantage of using CrewNerd versus the Speedcoach XL2 is the accuracy, stability and responsiveness of the pace readings. CrewNerd works off of the GPS in the iphone. This provides position data on a 1Hz basis, and the application uses this position data to deduce the velocity. By comparison, the Speedcoach GPS2 has a GPS capability that provides 5 updates per second. The impact of this is that Crewnerd needs to use significant smoothing to stabilize the coarse position data. This causes a significant lag, up to 10 seconds between a velocity change in the boat and the pace display on CrewNerd showing a stable, accurate pace. You can crank the smoothing dow, but then you end up with pace readings that essentially oscillate around the actual pace.
The good folks who developed CrewNerd recommend that the best way to get more accurate and responsive pace display is to pair the iphone with an external GPS receiver. They recommend the Dual XGS160. This provides 10Hz position data. When paired with this receiver, the pace display responds quickly and settles well.
However, CrewNerd seems to be unreliable with the XGPS160 receiver. Sander (of “Rows-And-All” fame) has previously described having hangups and the freezing of the CrewNerd navigation display when using the receiver. This morning the same thing happened to me. I was 11K into a 14K row, and then the pace and distance displays stopped updating. The HR display was alive and displayed an accurate number. I’m not sure what’s going on, but I am not sure whether it is better to have a laggy pace display or have the app stop functioning in the middle of a practice or race.