Re: Now I've seen everything . . .
I agree that there are some applications where they help. I guess I believe that there is always a better fix: trim, weight shifting (tiller), height on transom, trim tabs, propeller etc.
When I see one on a 225, I cry, when I see one on a 5, I laugh . . . Like I said, maybe I should test one but I have never seen truly favorable test results. They almost always slow down a properly set up boat.
Howver, with adjustable trim tabs and SmartTabs, planing speed is dramatiaclly reduced, in my case a 20 footer and two 23 footers, planing speed is down around 12 MPH, and a reasonably efficient plane around 13.5. Trim tabs have no negative impact on top speed if installed correctly. Trim tabs, Doelfins, hydrofoils etc. can all mask a problem. I do not personally believe that the fins can enhance a boat that is right. It is entirely possible that I am wrong.