TBayRay asked the question on the "3 hole Tuttle fin" in the new 2011 Rio boards.
I checked with Tiesda You (Starboard Brand Manager and chief design engineer).
The 3 hole fin was requested by a large rental/school operation in Fuerteventura.
They must install and remove the fins every day from their rental boards so they
asked for a "single screw Tuttle fin" to cut the screwdriver operations in half.
Starboard responded with the "3 hole Tuttle fin" which can be installed with just
the center screw, but also can be installed conventionally with 2 screws.
The fit and angles of the Tuttle and Deep Tuttle fin boxes and the 31 and 41
cm cleaver fins that come with the Rio boards remains the same.
I have found that if you fit your fins correctly, so the sides of the Tuttle fin
root are a "push fit" into the fin box, and that front and rear tapers are really
fitted with max surface area contact, then the tapers and side fit will take
all the loading on the fin (even up to 70 cm formula fins) and the screws
(or in the case of the new 2011 Rio boards "the screw" singular) only serve
to draw the tapers into full engagement and prevent the fin from falling out
if you strike something in the water.
Hope this helps,