Are you sure your speedo is correct? I don't have the StarGazer, but my PP's have always
been accurate -- depending on how they are calibrated. What I mean is that if I have
spent the time to calibrate for 23MPH, it's very accurate there, but might not be at 34MPH,
or 16, but I imagine if I calibrated for 34, it would be very accurate there, but probably not
at 23, if you see what I mean.
The owners manual should have instructions on how to calibrate it - I use a handheld GPS
to do it. I have not ever had any luck having it calibrated across all speeds, so pick where
you ride the most often and do so for that speed. (it's usually very accurate +-4 MPH from
where mine is calibrated).
I always keep the handheld GPS in the boat just as a monitor, it's mounted with a RAM-Mount.