Motionx Not working well for short Sail Races

According to some developer forums, the Iphone refreshes apparently every 5 seconds. From reading around, it looks like the refresh rate is so bad, we can't even use the Hz measurement.

I have been testing the iphone app motionX GPS on my Wednesday night racing and comparing it to a 1Hz Garmin marine GPS. The knot meter fluctuates by 4 knots and our VMG and bearing aren't accurate either.

The average readings are accurate, but this isn't good enough to allow us to make tactical decision on a several mile long race course.

A refresh every 5 seconds might be perfect for highway driving, but this is going to be terrible for quick sequential turns.

Maybe developers can make the GPS readouts better by artificially simulating 1-10hz gps through the use of accelerometer data.

VMG bearing, Iphone sailing App, MotionX

I think I might have found our new Wednesday racing VMG tool for those of us who are iphone users. If we use this heavily, it might be worth while to get a waterproof cover with wrist/pocket strap or something. It looks like it will be very easy for us to enter in the marker letter’s lat /lon and then track bearing, VMG, time average speed, distance.
Here are some other boats that are using this:
Transpac, Columbia River Oregon:
View Race path in google maps:

I hope to use this two Wednesdays from now and will post results, if successful. My biggest concern is loosing my iphone overboard. Maybe there is a retractable strap that could clip inside the bottom of my shirt pocket and then connect to a waterproof iphone case.