I'm using an expensive equipment which measures and records the following data when I was on a ship and did some sailing:
GpsTime, GyroX, GyroY, GyroZ, AccX, AccY, accZ, Heading, Pitch, Roll, Latitude Longitude, Heave, V_East, V_North, V_UP.
What I'm trying to do: I'm trying to predict the Roll, Pitch and Yaw from AccX, AccY, AccZ.
What I've tried: After reading some tutorials I found that the following equations are wrong and I'm not sure why, any ideas which equations will work?
pitch = 180 * atan2(accelX, sqrt(accelY*accelY + accelZ*accelZ))/PI;
roll = 180 * atan2(accelY, sqrt(accelX*accelX + accelZ*accelZ))/PI;
AccX, AccY, AccZ can give you pitch and roll but not yaw. The answer they give for pitch and roll will also be subject to errors if and when the detector itself is accelerated (a foregone conclusion unfortunately if you're on a boat/ship).
GyroX, GyroY, GyroZ give you an independent answer, this time for all 3 angles: yaw pitch and roll. But this new answer is subject to drift error which grows over time.
The trick is to combine these two answers because they are complimentary, the gyro's strength is the accelerometer's weakness and vice versa. This job of combining the two, called fusion, is handled for you by many detectors if you know how to extract the fusion result. If you're using an MPU-6050 for example, you have to make sure you're getting the result from what's called the DMP (where the fusion happens). The fusion result is typically in quaternion format and the trick then is to make sure to use the correct conversion from quaternion to yaw pitch and roll.
Finally, just as the gyro was fused with the accelerometer, the result of that fusion can in turn be fused with results from the GPS or magnetometer (the other readings you list like V_East, V_North). This second fusion should help with yaw accuracy (the yaw was left out of the first fusion).
This is all explained in detail in the following tutorial:
https://youtu.be/k5i-vE5rZR0
You don't need expensive equipment for this by the way.