I tried taking p3p up yesterday while fishing from a friends boat.  I didn't want to loose it in 800ft of water so I installed some floats( noodles on landing gear as seen on YouTube) just in case...at least if it went down I could recover.  The ocean was perfect...dead flat( never happens), first flight it immediately started to drift, this was a fast drift and you had to really fight it or it would fly away.  Tried recalibrate compass, remove the floats and still had drift, tried 4 different flights all with drift.  Brought back home on land, did a compass recalibration and flew perfect, just like the previous 100 flights.  Any one experience this or have tips for flying off boat....I wanst sure that on power up if the rocking boat was causing a bad calibration?  Also if I had switched to ATTI mode would the drifting stop?( I was planning on learning Atti mode over the next few weeks for this exact reason).  The boat captin says it is the Burmuda Triangle and nothing will work right
Just Fyi we were about 8 miles offshore for first try's and 2 miles the 3rd. Had full gps signal and flying gps mode.  Also on latest fw and using iOS.

could have been because of the electronic compass on the boat

Did you have VPS on?

VPS was off.  I checked that after the first flight.  

Sounds like metal interference for sure. Best to do the calibration at shore, and perhaps do a quick take off test to make sure there is no issue with calibration. They say you don't have to calibrate within 100 miles of your last good calibration, and that it is probably preferable not to.

That said, I reckon your issue will be interference from metal on the boat at the take off point. Check your mod values before take-off, and if they are out, don't bother. Try a hand take-off instead.  .

The phantom will always drift in ATTI mode - be it because of a slight breeze from nature, or the uneven wash from the phantom itself. Learn to fly ATTI mode for sure, as you'll need it some day.

One issue might be that the boat is not level.  (Because it's constantly moving in the waves.)

When the Phantom is powered up the IMU assumes the ground is a level reference.  On a boat the ground is never level.  So the IMU gets a faulty level reference.

The first flight I did not do a compass calibration, as I was 30 miles from last flight location.  The boat was a 28ft open fisherman, so there was not a ton of electronics or metal.   Now what Fulgetrite mentions about level reference would be a factor....I can tell you for sure that even though seas were flat,but the boat still had a considerable rock to it.   Now at what point IMU look at the ground for reference?  Sometimes I power on my craft before setting it at take off position, so my guess would be that it would have to do that right before take off?  What mod values should I be looking for at take off? Thanks.

It's hard to separate fact from fiction in these forums as opinions differ, and it's hard to find a definitive source of truth - but I see:

Gyroscope Mod should be around 0.00
Acceleration Mod should be around 1.00
Compass Mod 1400-1600.

Acceleration and Gyroscope will probably fluctuate a little on a boat, but I imagine that is to be expected with swell and current.

I do recall seeing a post from a previous boaty and he had no problems hand launching from his boat. The same for some guy that worked on a sea based oil rig which is predominantly metal. Do a search.

Are you sure the P3 was drifting away and not the boat?  It would be hard to tell out that far with no reference points.  Just a thought.

Fulgerite Posted at 2015-7-20 02:06
One issue might be that the boat is not level.  (Because it's constantly moving in the waves.)

When ...

That does not seem to be correct.
Why do you say that "the IMU assumes the ground is a level reference"?
Are you making that up, or just guessing?

Why do you think we do IMU calibrations?

aek Posted at 2015-8-5 04:01
That does not seem to be correct.
Why do you say that "the IMU assumes the ground is a level refe ...

Each time you power up the drone performs a re-calibration of level.

The IMU calibration is for optimizing noise level gain settings.

Fulgerite Posted at 2015-8-10 01:22
Each time you power up the drone performs a re-calibration of level.

The IMU calibration is for o ...

So, what you are saying is that if you don't have a perfectly leveled surface to take off from whenever you are out flying, the copter will be drifting away...?

Do you have anything to back that up with? A document? A link? A page in the manual? Anything...

Just experience.