I test my boat yesterday, if distance between two points is short, there will be a "S" track. i tuned the following parameters but has no effect.
Distance between point 1 and point 2 is about 20m
Distance between point 3 and point 4 is about 30m
find more help from the developers here http://discuss.ardupilot.org/t/correcting-a-wobbly-path-between-way...
I want to build a similar boat like your, how do you design the motor's servo
We're trying to move support over to http://discuss.ardupilot.org/c/arduboat
You might get a better response in the support forums