Could be a mix of over correction and prop torque, to fix the prop torque the trim tab should be angled down on the props rotation side to counter this normally 2 degrees as a good start, straight line speed should be tested to ensure the boats riding correctly on the very edge of the sterns ride pad using mostly the trim tabs as the ride surface, this also keeps the turn fins out of the water until the boat tilts for the turn only then should they dig in to help in fast hard turns, any amount of drag caused by turn fins touching the water before the boat tilts over can result in wobble.
Honest racer advice .. scrap turn fins and use a slightly longer rudder! or if you must use them then only use one on the direction of the turn, most races are oval laps so only one direction, I've seen race courses use both left and right turns but honestly those just ask for accidents.
If your using a decent hull the chine rails should be perfect on the edge of the V which should dig into the water on a turn but due to the flat on the under side of the rail it traps air so when you pop the boat back to straight the boat should literally twist up and flat instantly this trapped air also help stop the boat from flipping over!!!if using fins then you will roll the boat over a lot more as they are dragging and catching the water.
Over correction is usually caused by ( the driver) high speed servos making that rudders movement all so dramatic at speed, it also probably isn't helpful to have a solid direct link to the rudder, the rudder linkage should have a ---V--- shaped bend in it to remove vibrations and rudder twitch from passing water, which in these boats the slightest twitch can see your boat into the wall.
( Just a head up this is the info my dad gave me when i started racing, and he was UK champion for many year running during the 60's and 70's when races were 2 hour endurance's, on 4 stroke engines!)
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