Hey Bill,
Wrt, fin lift, are you talking about fin foil lift as it relates to Bernoulli? If so, on a typical bottom turn where the surfer gets “thrust”, what do you think is the angle of attack (incidence) range acting upon the foil? This matters a great deal wrt foil lift or high pressure hold.
Aloha Craftee
I don’t think the “thrust” I was referring to was limited to bottom turns. Properly placed fins on a tri fin develop “thrust” over a typical single fin, In all positions on the wave. The biggest reason for this is their better “lift” generation over a common single fin.
As to AOA. I remember years ago, like 35+, when sanding some dagger boards for a large Catamaran for Phil Edwards at Hobie, a discussion with him about angles of attack. His view was that most foils couldn’t be made to work beyond 30 degrees AOA and that a typical surfboard often was dealing with AOA up in that range. He felt that even a longboard trimming forward on a wave was experiencing extreme AOA as the water was rushing up the wave near perpendicular to the direction of the boards travel.
Neither agreeing or disagreeing with Phil on this issue, the point I am making is that among knowledgeable board builders, these issues have been analyzed and known for a very, very long time. Surfboard fins are and have been, fairly well understood, among those in the know for a very, very long time. Fins are long evolved and pretty much matured in their current states.
So to answer your question. I think I would agree that the lift generated solely by the angle of the fin is more noticeable then the effects of the quality of the fins foil. You will notice that that is why I referred Burnsie to my previous posts regarding fin angles.
My posting the fin foil photos, was that the work on them just happened to coincide with Burnsie’s question and seemed a good time to add the foil info into the mix also. Neither were meant to upstage the other in importance.
None of this makes the angle more important than the foil or any other aspect of the arrangement of the fins. Each and every part is important in making a good riding board. It is very hard to measure which has more value. The determinations are going to be highly subjective as very few people have the kind of experience needed to make those assessments without prejudice or at least with so little prejudice that their opinions carry measurable value beyond interesting office cooler babble.
Its a Bernoulli v. Newton argument.
http://www.grc.nasa.gov/…irplane/bernnew.html
just so you understand my position, any flat unfoiled object has tremendeous lift capability determined by its surface area and (high) pressures acted upon by the moving fluid medium…in our case high density water has a very high pressure effect on the side of the fin and the redirection of flow (like sails on a sailboat) is the main cause of thrust. IMO, foils offer streamlining, which reduces drag at low AOA and makes fins more efficient. If all one did was to turn very hard from one rail to the other, flat sided, zero foiled fin with rounded leading edges and thinned trailing edges work just fine. I believe Plus One (George) has done testing in this area with good results.
In a nutshell, wrt fins and foils and lift, Bernoulli is grossly overrated, and Newton is grossly underrated. Or put more accurately, its mostly Newtonian on medium-hard railings, and Bernoullian everywhere else.
Until someone publishes a tech paper, backed up with scientific testing, accurately describing all relevant water flow angles acting upon the bottom surface of the board, this is just healthy debate. Your position is just as good as mine. 
We are all capable of opinions. Though I am not sure they are all equal. I enjoy reading everyone’s, no matter how whacky they sometimes are. Entertainment is a good thing!
In the end, the only thing that matters is how it works in the real world and every one’s “real world” experience varies. I am lucky in that my “real world” happens to be the North Shore.
I could pretty much care less if there is a “white paper” on why my boards or fins work. It might be an interesting read and might spur a new idea. But trial and error, in a hands on environment, with great waves, surfers and boards keeps me pretty occupied and is hard to beat in the laboratory or around the water cooler.
Still, I am in touch with guys like Tom at Daum Tooling and his software testing and quest to improve molded fins. I am not a stick in the mud. But depending on how much real world water time one has access to, the white paper approach may be their dominant way to explore designs with.
Foil lift does matter, we might just disagree to its level of effectiveness.
It all matters, I don’t try to measure how much each one does more than another. I will leave that argument up to you and others who might find it entertaining. All details matter because they all effect the whole.
Cheers
