My spray pump boat could not go straight

Hello. everyone
I’m sorry for my english. im a chinese
My boat is a spray pump boat. I found some problems during auto mode,it could not go straight. I try to adjust PID,but it doesn’t work. I think it caused by inertia when the boat make a turn,the boat always deviating from the route and the pilot constantly adjust. i think it is spray pump structural problem,should i change it to skid steering? or have some resolvents?

I have no experiences with boats (mainly copters)
but i would calibrate the compass

Did you read thru the instructions for Tuning Navigation? You really need telemetry to do this efficiently. I have tuned Rovers in 20 minutes or so using this process.

Skid steer is not appropriate for a motor/pump/thruster and steering servo setup.

Seconding both recommendations from @J_B1 and @dkemxr. I know you said that you have done PID tuning, but its easy to get that wrong. My boat’s path-following was much worse than yours until tuning. Of course an accurate compass is a pre-req. In the following images you can see how my boat’s path-following was bad, worse, then pretty good after tuning. I would suggest giving the tuning another go and report back.

  1. Path following with no tuning

  2. Tuning process

  3. Testing it out

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I have constructed a large boat myself. I have adjusted the PID for a while, but have found out that I have a lot of disturbance from other electrical component onboard.
It takes me 20-30 minutes just to get the compass in correct orientation. Then my boat will steer as in ekrell1 last picture.
Do you guys have the same initial problem with the compass? My boat is pretty heavy and are steered by two engines.
Also, I get different cruise speeds just by switching from auto to manual to auto again (from 1.6 knots to 3.5 knots). Any suggestions what that could be?
Last thing, after a mission it sometimes stops, but sometimes it speeds up to 4 knot going just straight (crashed the boat one time).