I recommend you give these steps a try:
1) Double tap the chart anywhere to start bearing/distance measurement. A double tap (or single
tap) is a common gesture with iPhone/iPad.
tap, the green circle on the chart. This tells iNavX
that the origin of the measurement will be the device position. This original will then track with the changing position of the device (vessel position).
3) Drag the red circle for a bearing/distance measurement. The bearing and distance will be shown at the top of the chart. Single tap anywhere on the chart to end measuring.
I think it would be unwise to assume every distance/bearing measurement a user wants to perform originates from the device (vessel position). As such allowing the user to single tap to let iNavX
know that is what the user wants does not seem unreasonable or kludgy to me, but understand such as yourself have different expectations.