We always tried to place the fin at the CG.  If you do that it depends on where the CG is most of the time and when you want the best handling (full of gas, people etc.)  My old Daytona had a fin structure you could move the fin about 18". We just didn't know where the best place was since we were the only ones trying to make a tunnel turn (it turned VERY WELL thank you.  Single blade chisel point leading edge about 5" wide (tapered) and 10" deep(?). Fin too far forward makes it want to hunt too far back less effective. I don't know the rule of thumb nowadays though that's strictly old school.

lift strap and fork lift to find CG. ?
Where to buy fins?

tom (wizard) and craig told me they did it with a 2x4 on a car jack while the boat was fully gassed and with the fully suited driver sitting in it and this process worked perfect.

glenwood marine has fins for a decent price. http://www.glenwoodmarine.com/ so does www.rexmar.com or www.cpperformance.com so does anyone else who buys through them.

Brad's right on. We balanced the boat on the trailer using said piece of lumber ( I'd use a 4x4 to be safe) between the trailer bunks with a floor jack to take some of the weight off the " point load" on the bunks. Used an A-frame to lift the bow eye high enough to slide the wood into place.  Be careful not to get your arm between the boat & trailer in case something lets go. Have help handy.

Thats what I did . 

-beerjet-