Waypoint accuracy

Hi everybody
I want my bait boat to go to wp very accurately.
Now the problem is if I record a wp in the morning, after 4-5-6 hours the wp slips to the left, pretty much. After 10 hours 10-15 metersI think the log files can help with that. What should I look for in the log file and what parameters do I need to set for the bait boat to arrive at the waypoint exactly, even after 10-24 hours.

Maybe it is the gps position that changes during the day, it can be inaccurate up to 10-15 meters. Probably an rtk with rctm correction would solve the problem.



Thanks for your reply Corrado, rtk I will not use, too expensive for me. If you have a lot of satellites bait boat accurate.
I just want to know what to look for in the log file, which shows that my settings are good. The tuning steering and throtle are perfect. Is there no other factor that affects accuracy?