i have used one . realy can`t tell a lot of difference . i put a T&T on my boat that helps most of all . the boat i have now don`t have one . i have one on a old motor i think i will try . i have checked my speed with a gps . will put it on and see if it helps speed or hurts it .
my therie is if it helped all boats they would make the finn on all like that . so i think it depends on the boat set up and dezine. check out this link
http://www.themarinedoctor.com/cgi-b...action=search2