SRFDCO Fin.

Inspired by other fin designs, multi element plane wings and F-1 styling.

I don’t get it. Unless it’s spam, why pump something in advance?

pfffft

 

So looking at surf fins most of them are dorsal shaped. Most are placed to function with the other fins but not as closely as Herb Spitzers Superchangers, or the Twinzer.Those particular setups have the fins close enough to interact with the flow of the other fin so there is more than one dynamic element working to create a hydrodynamic function that can’t be aquired with  a single fin element.

You can’t get the feeling of a Twinzer without using the canards in front of the larger fin. They use the basic dorsal fin shape but by using unique configurations they create a unique quality of performance.

So will you be discussing the design elements of these new fins, or will it be a business venture where you will be offering these fins for sale?

Phebus, I’d like to discuss the fin and how and why it works. What people think is always interesting. 

They’re not for sale but I did sell a few prototypes to pay for materials. 

Neil Purchase Jr. is making a board with 2 fins about 6" apart. It’s not the same as a twin with fins out on the rail, and it’s not the same as what Bill Thraikill does with 2 fins about 1" apart.

I’ve made a board with 2 fin boxes 1" apart, and I’ve made 2 boards with 2 boxes 6" apart. I’ve only tried double foiled fins on these boards. I had no noticeable negative issues with Bill T’s setup, or with NPJr’s setup using stiff fins. I found it interesting that I needed to keep the fins back on the board with NPJr’s setup, or I could make the tail slide out. I started with them where it looked good, but it was releasing every time I pushed hard into a turn.

I tried using flexy 7" FCS dolphin shape fins on the 2nd NPJ style double, and I don’t like them at all. I didn’t try the fins from NPJ #1 because I gave the board to my brother. I’m in the middle of making a set of stiff single foiled fins to try on the NPJ #2. I think I cut out 7" bonzer style center fins instead of the Smith/Parrish/Brewer style I have on NPJ #1. From images I’ve seen, I think Bill T’s fins have a similar shape to the Bonzer style. I also noticed Greg Griffin makes a single with a similar shape and I think Griffin makes really good fins. I had made a set of 6" double foiled Smith/Parrish/Brewer fins, but they seem a little short. 7" looks better, and I’m hoping the slight difference in the bonzer outline will be a plus.

It will be interesting to see what happens with the foiled side facing out compared to the foiled side facing in. I think Bill recommended having the foiled side facing in.

Funny I spent the better part of 2 hours today with Bill T. I had a wonderful time talking about surfing, boards, people, wipeouts. I have a lot of respect for the things he’s done with the people he’s known, and what’s he’s learned about surfboards. I think he’s learned things the hard way, and that’s by doing it yourself. Gotta respect that kind of knowledge.

Bill passed on a thought about fins… go wider. I have a piece of 1/2" maybe 3/4" thick G10 that will become several singles, one will be a 9" Stage 4A. I’m not sure what the rest of the panel will end up, but they won’t be the 3/8" standard single fin box width. I also have a couple of single foiled fins that are at least a 1/2" thick. I need to finish those too. I glued foam to a 3/16" panel then added more glass to the foiled side after shaping them. It will be like splitting a 1" thick fin into 2 pieces. Be interesting to ride that then switch to the standard thickness fin and see if I can feel a difference in drag.

sharkcountry wrote:

I’ve made 2 boards with 2 boxes 6" apart.

This would be close to the typical one chord length separation of biplane wings.  Biplane wings could be smaller, thinner and structurally lighter to achieve the desired performance.  They worked well for biplanes because of their slower speeds.  Surfboard speeds should have similar effects.

Quads with fins on the rails, close to an inch between them fore/aft, have a deffinate interaction between them, and the changes that come by changing the distance by a quarter inch in noticeable.

Other fin setups that I really like are Greg Griffin’s 5-fin fish and 3 in a line hovercraft. I have used my 5 fin board a lot and I really like the hold and way they tend to flow out of turns much more. The Hovercraft style 3 across is another great way to have a wide thick tail and have a lot of control. I tend to make spin turns with traditional short fish boards when coming off the top or cutting back, but the Hovercraft will make drawn out carving turns. It’s easier to jump from board to board when you don’t have to compensate for the idiosyncrasies of the boards. I’m thinking about using the 3 across setup on other boards to see if it will work on a variety of tail shapes. Other guys like Liddle and Dave Parmenter have used small sidebites inline with a larger middle fin.

I don’t know if it is board design or fin setup, but Greg’s fish boards are fast, and they have tremendous bite. I know he is very particular about the fins on his boards. All of our Griffin boards have custom made fins from Greg, and they are made for each board. You can put all your energy into a turn and not worry about the fins releasing. For older guys like me, it’s important. When the fins release, the sudden change in pressure can make my back twist in a bad way. Then I’m out of the water for a while. Younger guys or people in good shape may not have that problem.

Another guy making cool fins is Robin Mair. He puts a lot of thought into his fin design.

 

Taylor O and Sharkcountry,  Im amazed at all the great fins esp the Mairs, but last year I was keen to work out how that interdependence between very close set fins could be used as a side fin. This thread from a year ago came close…

http://www.swaylocks.com/forums/science-behind-thraikill-twin

So I started with the Twinzer and figured that if you put 2 std side fins side by side or in a staggered arrangement then it’s going to be too much area so I’d have to use 2 high aspect fins, around 4:1 (height to base) Shorter base fins move differently thru the water. Sure they have less resistance at the junction of fin and hull but they also create less drag as AOA increases, a smaller chord creates less flow separation so less drag.  That was the link with Greenoughs high aspect Tuna fins, for 2 fins the same height, the one with the thinner chord has less drag all along the fin.

 

With the 2 high aspect fins I kept them inside the template of a standard fin reasoning that a fin is not just a matter of foil and cant, that the template is just as important. Image 1.

Now the question was How far apart would be the most effective,  almost any arrangement would yield a result but there would surely be a position where the effectiveness increased and then decreased as they got too close and that’s what I found. I’ve tried variable distance between fins. See pic.

Now only was the lateral distance apart important but also the fore/ aft positioning, should the TE of the front fin and the LE of the back fin have a gap, be inline or overlap and that too became clear after a few experiments.

 


Apart from the Twinzer, the closest setup of staggered fins I found were from high speed car styling and aeroplane wing design. Obviously the difference in density would change how I put the fin together but the essence of using multiple elements to get the greatest effect is well documented and used to create greater lift, more down force or to delay flow separation.


If you are looking for input on fins closely spaced, I don’t have much to add. The Jobson twinzers and Rich Pavel’s speed dialer fish is where you’d want to look. Herb Spitzer would be a good source for input because he did a lot with his superchargers. Robin Mair’s quad setup I use has a close spacing. Take a good look at the little C5 fins from Futures, they have a concave inner side, it’s not flat, and they have built in cant. They are designed to affect the flow hitting the larger fins set just behind them.

There’s a whole other side of fin placement I’m looking at and that is multiple fins but not closely spaced together. George Gall’s assyms opened up our eyes to how fin placement will change how the board feels. The fins on the assyms tend to change how the disturbed water flow affects the other fins. His boards seem to move over the water a little easier. 

For noticeable lift, Griffin’s 5-fin is far away what I’d say is the most noticeable. The first time you ride one you will feel it. I know people who love them and others who don’t like them. I love them, but I think a lot of it has to do with Greg building the fins for every board he makes.

Sharkcountry, your information has added plenty for me to follow up, thank you. Those guys do it so well that’s why I went in the opposite direction to bring two fins in as close as possible. I’ve never seen a multi blade fin before but there’s precedence for adding angled surfaces from Starfins to the Elevon. The Elevon in particular becuase they’re chosen to add an extra surface but at the top of the fin. Sort of like a curved  plane wingtip but going up and down and sticking out at 90 deg. I haven’t seen a multi bladed fin before.

My brother likes to buy stuff. He has all of the funky fins with the “wings” from the star-fin Cheyne Horan was doing to the Wavegrinder, and the wavegrinder sidebites, and the FCS winged trifins. I haven’t tried them. I know several highly respected surefers who like the curved side fins.

This thread inspired me foil a set of fins today. They have the Bonzer outline, but I did them as single foils and will be trying them in my NPJr double fin. The older board I have with the Thrailkill setup has too many issues to use as a test bed. I’ll need to add boxes to one of my other boards for a better test of the Thrailkill setup. The bumop in the middle is a giant delam. I’ve since taken the deck off and fixed it, but it’s not one of my regular boards. I rotate between 6 or 8 boards and this one is not in the rotation.

Like your brother, I think I’ve bought all the new fins too !

The NPJr setup looks interesting, Im sure I can do a set of my fins for twins.  Funny that everyone can be hooked on McKee setups down to the 1/8 inch, and then it all heads in a totally different direction.

I don’t think that printing is an economical way to produce fins and the materials aren’t strong enough for real surf at the moment.

This is a pic of the basic level of 3-D finish that’s not exactly rough but not a class A finish either. All these different finishes on the one fin.


2 sets of single foil fins for my double single boards. A set of 5" double foiled for rears. The blue fins are 1/2" thick each side.

 


Sharkcountry, I’m looking forward to seeing your fins on a board. Do you foil a 60/40 or 70/30 ? Have you tried any inside foiling ?

The first time I saw a ‘‘fin with a fin’’ was in the parking lot at WindanSea, in 1957 !         It was a wood glass-on fin, and sprang from the furtile mind of Alan Nelson.       Alan was among that first modern crew that first surfed Waimea, in Nov. of 1957, and a regular fixture in the lineup at WindanSea.       Alan had shaped for Velzy&Jacobs, Hobie, Yater, Bing, and others.       I consider Alan to be a true genius, when it comes to innovative surfboard design.      Just a little info/history on our sport.       Carry on.