I have a warning to add on Doel-Fins or for any type of fin for that matter.
When your boat is up on plane Doel-Fins or any other type work great
up get you up on plane faster than no fin. You are also able to stay up
on plane at lower RPM.
The problem is that is a low speed below plan or close to it they tend to
make the boat lean to one side or the other. On some boats the lean
is so pronounced the boat looks like it will roll over. I do not know
why this happends but I have seen it on many boats including mine
that has a Doel-Fin.
Since I know the danger I never try to turn at speeds just above or
below planing speed since I know my boat will tilt heavily to one side.