That break in the leading edge's outline, with mini ish tubercle with lower aspect ratio to tip afterwards, is what i was attempting to draw the other night when infused with beer
opened the laptop for the first time in several days....
I've no issues eliminating the cutaway at the base of such a fin. I'd rather have the trailing edge vertical from hull.
I am afraid of too little base area, even with more depth, with such high aspect ratio fins. Could be an irrational fear, but slow speed drifty weirdness is a feature of high aspect fins, and reduced base width would seem to accentuate this. Tubercled fins being so happy in a stall/partial stall, only adds to this drifty weirdness. My multifin HWS's all seem to be overweight and dull until a certain speed is achieved then crisp and much more responsive, above that minimum speed. Any fin which prevents that speed to be achieved initially, seems to ruin the ride and make me wish I chose to ride my longboard instead. I refuse to hop or spastically try and generate that minimum speed on weak waves where one needs to get some parallel to shore movement early in the weak wave, avoiding the bottom turn.
I've never tried curved rail fins, don't know what to expect.
I can use the probox inserts for different cant/splay/camber and with no canted tabs I can more easily reinforce tab(s) with carbon rods. Not really big on fins sticking out beyond the apex of the rail. Having cut up my feet in my youth on such fins, ruining many a session.
As far as cambered foil rail fins I only have experience with the latest 'batfin' I made with the ~150% thickness drela AG10, and the jury is still out as to whether I like, it with only a few sessions in undersized underpowered waves. I am bothered by flat sides from a design standpoint, but still like their crisp responsive projection when underfoot.
The more 'antiflat' the inside of a rail fin is, the less I've liked them, unless in the rare more powerful larger conditions.
I am leaning towards the raked tip of traditional 'dol-fins' being a feel good 'suspension' with self centering 'caster' built in, with the tip flexing away from load and rebounding afterwards, with an acceptable amount of drag. High aspect with no tip to bend in reaction to the flow around it might have noticeably less drag, but is missing something, like the board not self centering to nearly the same degree and having to consciously do it, where that was never a consideration in the previous 37 years of wave riding experieneces. With multifins perhaps the rear fin(s) can provide that self centering and forward rail fins be optimized for max grip minimum drag, rather than 3/4 similar shaped sized fins of today's perfomrance quads and thrusters. I certainly liked the feel of mrMik's half sized Deaweeder fin in my thruster box which has a fair amount of sweep , with my HAR rail fins.
The ultra short turning radius of high aspect fins on my shortboard, when pushed hard, has been a bit weird to figure out, and makes one realize just how much resistance to turning the traditional fin outline imparts. Quicker and looser and different might be just be a short lived novelty if one cannot get it figured out and achieve the lines one intends when reading the wave face.
A happy middle ground of high aspect fin ratio and comforting raked tip's self centering and rebound twang is likely quite personal. Combining high aspect ratio's lesser drag combined with the comforting flexier self centering raked but draggier tip, likely needs a lot of trail and error to refine.
I think the deep 'Peng Wing' rail fin might be really fast and loose but still lack the comforting self centering and 'loading the fins through a turn' feel.
Can the center fin tame the turning radius without imparting too much added drag?
Can a thick foil counter the lack of self centering and slow speed drifty weirdness of high aspect ratio fins?
I guess there's only one way to find out, and that's to try it.
One of the most insight-provoking videos I have ever seen was the one where a penguin dives deep under the ice (carrying a camera), then cruises at depth, hidden in the total blackness, like a falcon hidden in the total brightness of a sunlit sky, then the penguin 'freefalls' upward to assassinate an unsuspecting ice-fish.
Do not skip the meerkats, or anything, if you want to learn how fins work.....
There are many interpretations possible when doing biomimicry designs. As a side project I am modeling a series of ocean animals inspired fins (thanks for bringing penguins to my attention btw), while trying to stay as close to reality as possible. I'll only allow myself to smooth the planshape to remove particularities that are variants among different specimens and design a better foil while respecting the original thickness. This is not a project to do revolutionary fins, but just to play with sticking various animal flippers and wings under your board. Plus it's pretty and a good study exercise.
I chose another picture (there's so much variations between species and individuals) and designed a thruster set. Went for the 7" depth suggested by wrc68, which gives a base of just above 3". Made two 18% foils, one symmetric and one cambered, that looks really thick on a fin but I let nature do the design for this project. Curved the side fins just a bit (about 1/2" from straight line), 7 degrees cant, and added some twist toward the tip. The leading edge has 3 degrees less AoA toward the tip, meaning less lift, less tip vortex and somewhat delayed stall.
PS: wrc68, if you gave some thoughts to the tuberced (curved?) thruster set you wanted we could start designing it. I didn't get G10 yet, being carefull with money because of the lockdown and delayed payments from clients until India's borders open again.
We Are One
Those look pretty sweet. Very close to what I was trying to draw on cardboard. I was looking more for a obvious break in leading edge outline half way up with a super subtle tubercle.
I was going to look for different breeds of penguins online, see what i could find, see if I could get my printer to work and get something printed up in the 6.5 to 7 inch deep range. I lost my round tuit though.
I very much like the idea of the rail fin tip having 3 degrees less AOA. I've an acquintenance who rides some fins with that feature, and swears by them.
Regarding tubercled thrusters fins. I do not really know where to start. The 50/50 gwhale fins cut to 4.5ish inches deep, are too weird as rail fins, and are my only experience trying tubercled rail fins, and they were so love/hate, the few surfs I tried them in.
I want very High aspect ratio but 'some' raked tip area, allowed to flex slightly.
I also am fretting more and more about big old tubercles catching and not releasing the leash, not only when getting into waves, but when actually falling losing the board and using the leash, I think the leash will be able to rip fin/ finplug out of the board. Leash shedding ability is becoming more of a consideration for my shortboards.
On my LB I have never used a leash with a tubercled fin so it was never an issue, but on either SB or LB, I have a tendency to paddle deep as I can at oncoming wave, sit and swing the tail into wave, and do the buoyancy assisted take offs, and the leash is very obstinate about getting wrapped around the tubercled thruster fin doing this.
Not sure the whole leading edge 'needs' tubercles either, perhaps just closer to the base, or if all three thruster fins need them.
Man I feel like I missed something. When did whales turn into peguins? Just kidding, WAO and WRC you guys are like a couple of mad scientist. Let me know when you two start a fin company. I'll be the first to invest!
I spent my free time this week making this fin. This is just a sneak peek and not finished so don't be too harsh. It's also meant to be a show piece more than anything.
MrMik and WAO are the scientists, I'm just mad.
One also has to consider that penguins will not fall onto the pointy end of their wings.
But surfers will occasionally fall onto their board's fins, and they use leashes.
The Dea-Weeder fin was my first attempt to make a tubercled fin that does not catch a leash or seaweed. It's tip is too pointy for safety though, maybe it can be rounded without causing issues.
The G-Whale and Albatross-Whale fins are rounded everywhere.
I wonder if a fin with smooth leading edge, but undulating surfaces would have some of the attributes of tubercled fins, but without the leash catching effects.
I really need to glue the carbon bars into the G-Whale fin that has WAO's smooth surface structure and find out if it surfs much different from the one with finFoil-generated undulations.
I could try to overlay a tubercled fin with a finFoil-undulating tubercled fin so that there are no actual serrations at the leading edge, but the Gullwhale fin without tubercles also catches the leash, albeit half as often.
The deaweeder is a good fin, its just not as quick or loose or forgiving as the GWhale.
It's way better than my regular dol-fin while feeling similar during turns with that forced longer turning radius, while being quicker too.
The Deaweeder cut in half with a probox base is my current favorite thruster center fin, and part of that is it will not catch and hold my leash on the swing late buoyancy assisted takeoff, but it also feels like it has more squirt/projection on the bottom turn than the top half of the Gwhale. It's not as loose but that's not a factor with my HAR 'sharky' rail fins with their extreme pivoty tendencies. It's also not as fast when on open face with good speed already, and able to pump for even more speed. The 0.5 Gwhale fin in such a situation with the sharky rail fins, make my board a freaking rocket. My issues are just getting enough speed in weaker conditions to where the board and fins come alive.
Breaking my 'minimum chest high' before shortboarding rule has been enlightening, and frustrating.
I finally got some good waves on my lumpy spitfire fin. It is significantly different than anything I've surf so far. It will definitely take some getting used to. I had it in a 9' x 24" x 4" longboard that is my daily for smallish days. Surfed diamond head cliffs and it was shoulder high sets, kinda windy, but great day overall. The good news is it's fast and trims awesomely. Just pick a line and you go. The bad news, it's seems to be unturnable when it gets going. It seemed to be impossible to break the line once it got going. I think I can move it back further in the box to try and loosen it up.
On the note of boxes, just curious if anyone has connected 2 bahne boxes together in a line for a super long box? It was a random thought I had as I was looking at my fin placement.
As far as biomimicary, I was thinking about either a quad or twin set of sea turtle keels using the turtles back flippers. I added a picture.