I find it interesting how they compared the G5 and M5.
The G5 has the worst foil of any surfboard fin sold.
Shoots, probably the worst fin ever sold. The groms sucked it up tho.
The results would not have been so ‘significant’ if they compared the M3 with the G3000. Another nice foil is the Rusty.
Re Blakestahs comments about the lack of thrust feeling on bigger boards…
two ways to get it…three fins isnt enough + lighter board…then there might be a chance of feeling it.
is there any downside ,or negative consequences to inside foils ? i was thinking inside foil would create more drag…but what do i know ? al byrne has some interseting opinions. the editing is appalling, but if you read it twice you get the idea at http://byrningspears.com/news-allan-byrne.php
Re Blakestahs comments about the lack of thrust feeling on bigger boards...two ways to get it…three fins isnt enough + lighter board…then there might be a chance of feeling it.
I’m no surf star but I can definitely feel the “thrust” difference in a 2+1 longboard over putting a larger single fin only on the same board. Perhaps one reason is that I ride the 2+1 with the center fin pushed way forward in the box and this gives a fin cluster that is closer to typical shortboard fin layout than the center fin way back that a lot of longboard dudes use.
I find it interesting how they compared the G5 and M5.The G5 has the worst foil of any surfboard fin sold.
Shoots, probably the worst fin ever sold. The groms sucked it up tho.
The results would not have been so ‘significant’ if they compared the M3 with the G3000. Another nice foil is the Rusty.
Re Blakestahs comments about the lack of thrust feeling on bigger boards…
two ways to get it…three fins isnt enough + lighter board…then there might be a chance of feeling it.
I always thought it came down to the increasing difficulties in riding hard on the tail and getting a large AOA on the fin cluster on a longer board.
Longer boards just don’t turn as easily…ceteris paribus. But I have seen obvious thrust on 3 fin longboards from very good longboard surfers…there was one guy who came up from La Jolla, competed at the Lane without wetsuit 2-3 years ago, and won the contest, who did classic longboard moves and could pump the crap out of his longboard…
And there are clearly shortboards on which you cannot find it at all… I have a used 6"4" Patagonia rocketfish 3 fin board that is absolutely thrustless, no matter what I try I cannot pump it and get a squirt, it is only a 6’4" (and flexes TOO much), but just because a board has three fins doesn’t mean you can generate thrust on it.
Okay, well, we’ll be needing pics of that little bugger.
Craftee,
Wouldn’t it also have been nice if they had written at what Re number the tank tests were conducted at? It would make a huge difference. I made a spreadsheet to calculate Re numbers typically seen by surfboard fins; I got a huge range, depending on how short a chord length you are willing to go to, and the size waves you generally ride (speed). Most fell within Re 90,000 to 1,000,000, depending on chord length and speed (of course). Considering the waves we get in TX, we are dealing with Re usually less than 500,000. This means foil shape and accuracy actually make a bigger difference than at ‘normal’ Re (like over a million or so).
Unfortunately, all foils perform better at speed, which sucks for the windswell dominant Gulf Coast…
JSS
Hey Sandy,
That depends what you mean by ‘inside foils’. Flat, concave and convex insides are all considered part of the overall ‘foil’.
Flat inside foils offer manufacturers simplicity, and reduced cost. Convex inside foils (much like conventional aircraft wings) are more efficient in certain respects than flat inside foils at speed. When going slow, though, a flat inside foil has the potential to generate more lift, at the expense of slightly more drag. Concave inside foils have the potential for much more lift than flat sided foils, but at speed they are worse than flat inside foils, not efficient. That’s why they are seen on things like hang gliders and ultralight aircraft; they can generate lots of lift at slow speed. They also generate lots of drag, but ultralights and hang gliders just want minimum sink, not maximum go. They are made for minimum sink to keep the ultralight or hang-glider aloft as long as possible, while keeping the flight speed slow.
These are all huge generalizations. Foils can sometimes surprise you, and there are exceptions to this.
There are arguments for each type of inside foil depending on personal preferences and conditions, but it’s much better to think of the foil as a whole, as the outside part is in many respects more important than the inside of the foil, especially at low Reynolds numbers (small chord length and/or low speeds).
This is only taking into account foil shape. Fin planform can severely impact how much lift and at what angles of attack this lift is generated, as well as stall behavior. So, to fairly compare two foils, you must have the same planform. Otherwise, it’s apples and oranges. If you want to see how planform affects how a fin behaves, this is a good source.
http://www.flightlab.net/pdf/3_Three-DimensionalAerodynamics.pdf
Figure 1 gives you the overall picture, and the text explains it. It takes a while to get your head around it, but it is one of the best explanations for the behavior I have yet read (it doesn’t just say ‘because that’s the way it is’). In order to get more background, the lesson before it is good:
http://www.flightlab.net/pdf/2_Two-DimensionalAerordynamics.pdf
There are other good aerodynamic sites on the web, lemme know if you are interested…
Remember, even though water and air may be dissimilar, at equal Reynolds numbers similar flow conditions exist, and many parallels can be made. It took sailing craft (and racing car) designers a few years to grasp this (compared to aircraft, where most of the research was initially done concerning foils), and once they did sailing craft and racing cars started to change.
JSS
it’s all so confusing 
i hate fins now !
Sandy,
That’s why manufacturers generally offer products that work well in lots of conditions, not just optimized for one set of conditions…
Here’s a simpler way to think about it:
Convex inside foil (sometimes called 80/20): good for most everything encountered, can lift well at low speeds and penetrate well at higher speeds, but not optimized for either.
Concave inside foil or thick 80/20 foil: good if you are working and pumping the hell out of the board in small waves (you generate the speed, but if you stop pumping, everything stops).
Flat inside foil: Outdated, in my opinion. Take a look at model sailplanes of the 60’s and 70’s and ones of today. Why model sailplanes? They work at the same ranges of Reynolds number as surfboards do (have to fly slow to ride thermals, have to go fast to go from one to another thermal) Flat insides are only advantageous from the standpoint of the manufacturer, less work to be done. Again, only my opinion.
Hope this helps.
JSS