Have a 1997 SR 21 foot Advantage Step hull with a 454 @ 425hp. At 70 mph get a really bad prop walk. (really squirlly) Connecting rod went through the block and will be putting a 540ci dart 600hp motor. My question is for trim tabs to stop the prop walk with added hp. Can i go to big? ie. 30" or will some other combo be better. Options are 30" 24" and 17". By adding to big of a trim tab will I hurt the MPH. I am not worried about over kill becuase the is no price difference, just dont want to hurt the speed or performance.
24" tabs on a 21' boat should be more than enough. I wouldn't expect tabs to cure the walk problem, as walk is generally hull related. However, tabs will provide you some additional stability.
Good luck with whatever you decide and be safe