Had the 24 out for the first decent session and it's living up to expectations.
Great in shallow water, works in the chop, no weed worries.
Wind was up and down and not strong so had the 75 wide and 7.3 waiting for it to pick up. -it didn't, 15-18 and could have done with the 7.8.
No trudging back thru the mud at the end of the session!!!

You bet!
I'm loving the fangy fins, I'm planing as early as anyone else on the 28 and handling chop and weed with ease!
cant wait for a 5.6m day on the 65wide.

Well my first outing on the FF20 DAm good results! Did everything I had hoped and came out relatively unscathed from the razor back bashing I gave it. here is a photo of a delta after a couple of clips

Her is the DIY NO Bling after a big day hitting razor fish, if I hit 10 it would have been closer to 100!!




Just a couple of surface scratches. I use the razor fish as depth gauges they stick out of the mud & sand by about 10 to 20 cm so you get a click click warning as you get shallow.

here are my results for the outing

gpsteamchallenge.com.au/sailor_session/show?date=2018-01-06&team=123

Stoked Just goes to prove good all round performer, tidy Alpha and a nice peak.

Thanks Fangy for the work hope it pays off. I and thank full
Ah yea I forgot NO WEED under the Nose of the fin what bliss

YP1 said..
...........Stoked Just goes to prove good all round performer, tidy Alpha and a nice peak.

Thanks Fangy for the work hope it pays off. I and thank full
Ah yea I forgot NO WEED under the Nose of the fin what bliss

The NO WEED under the nose is down to your work when filing and fitting the fin to the base of your board. So that must mean you did a damn good job of fitting the fin properly. Good work deserves a jellybean

As for the Razorfish; the sharpness of their edges has got to be a really good incentive not to fall off when you gybe over a bed of them

Iain showed me his Universal Box Fangy Fin. The fin started life as a Powerbox, however Iain has added the two fore/aft threaded bolt holes to allow for its use in his Tuttlebox board as well. This is only possible because the fillet takes most of the load, (not just the base walls as per a conventional fin) and as a result it is important that the fillet is nicely adapted to the board surface. The flex and deformation before failure characteristics of the aluminium should provide plenty of margin of safety with regard to stress fracture. The board surface will be taking more compressive load, but the area of greatest load is safely located upon the fin box insert itself.
So big thanks to Iain for a really good fin hack.

Not every idea is a winner. I decided to make a 'foil on a strut' and explore the possibilty of increased efficiency by reducing drag and putting the foil in a cleaner flow. A FF24 was sacrificed and the design roughly cut out with an angle grinder. A quick layer of etch primer to I could photograph the curves more clearly and then it was time for a splash.
The fin worked well when loaded. It went uphill very happily and displayed no real vices. However, downhill it didn't feel any more slippery than a FF24 and ventilated badly at speed when confronted by thick weed. Even worse, it is possibly the worst fin I have made when gybing. It simply feels like some one has thrown out a bucket tied to the back of the board once the fin is no longer heavily loaded. The drag is depressingly real.

So atthe end of part one of this experiment, my conclusion is; at this point in time, keep your angle grinders cool as there is nothing to be gained by doing this.











I had fallen down the rabbit hole of the Theory of Lift. I had thought science had a handle on this one. It turns out that there is no academic consensus on why planes don't fall out of the air. Bernoulli's Laws apply well to laminar flow in a tube, but don't translate well to free stream flows and provide no explanation of stall behaviour. Newtons laws provide explanation for the final result, but some researchers feel they fall a little short on the explanation of separation from the upper wing. ( I am not sure I support this view just yet ) Fractal vortex flow may fill in the gaps, but at this point in time appears to be a nice idea, but has no hard research to back it up.

I don't feel as though I the tiniest fraction of creativity of Lewis Carrol, but decided to chuck all my ideas and thought bubbles down the same rabbit hole. I didn't have an Alice in Wonderland moment at the end, rather just another weird looking chunk of aluminium masquerading as a heavy weed fin.

This fin is typified by its massive cutout, and scalloped chord shape along the base. The premise of the design is that the junction of the board and fin occurs at, or very close to, a free surface. The flow here is very turbulent due to the large pressure interferences and I suspect, incapable of producing meaningful lift in comparison to the drag from the surface area of the fin along the chord width. Therefore, I aimed to reduce the energy loss from turbulence and surface area drag at the junction and move the active foil area into a cleaner water flow.

The end result is a 'strut' joining the fillet base to the foil. The inherent strength of the aluminium is critical in allowing substantial reduction in the foil base in both width and depth. This design may not be possible to replicate with traditional fin making materials. The strut is intended to be as slippery as possible and not contribute greatly to the lift of the fin. Its outline is closer to the NACA supercritical symmetrical foil shapes.
The foil proper is a standard FF. The trailing edge thickness is slightly greater and only slightly rounded in an effort to keep trailing edge vortices small in area and limit interaction with foil surface vortices. A secondary effect of the forward 'strut' placement was to try to induce a little twisting as the physical properties of aluminium seem to lend themselves to this behaviour.

Although it has become clear that my grasp of hydrodynamics is limited at best, I haven't given up entirely, I am going to muck around with the foil and the strut foil junction some more, but I have a feeling I may be trying to put lipstick on a pig. Another Top Ten Fangy Fail...

If I was you fangy, I'd try fairing in the front of the strut a bit better, at the moment there's a sudden change in curve just after the leading edge. This may be where the drag is coming from, only a thought, but there's nothing to loose by trying it. If you like I don't mind having a play with it.

decrepit said..
If I was you fangy, I'd try fairing in the front of the strut a bit better, at the moment there's a sudden change in curve just after the leading edge. This may be where the drag is coming from, only a thought, but there's nothing to loose by trying it. If you like I don't mind having a play with it.

well done mike, I was too polite on Friday to mention the dodgy grinding.
keep going ross until you get it down to an 18.

boardsurfr said..
Love the experiments. They can't all be winners, but it's just a question of time until something else comes out of it that's useful.

Seeing the cutouts reminds me of Lessacher's early experiments and "glass bottom" boards where he could film the bubble movements on the fin. The smaller cutouts work well because the bubbles get pushed to the other side before they can move up the back edge of the fin. With your deep cutouts and high angles, maybe they go up the other side of the fin, creating spinouts. That would match your observation that the fin works in high loads, but not low loads: only at high loads, the pressure differential is large enough to pull the bubble away. That's just a theory .. maybe be should revisit Mike's suggestion to build a glass bottom board next year when I visit .

I'd love to hear theories about why the fin works so badly in jibes, or even better see computer simulations. I doubt that the current programs are able to simulate the flow in jibes accurately, though, and you'd certainly need some supercomputer time if they did.

Wolfgang was specific when we talked about cutouts, 3 cm diameter. So it's possible you are correct Peter and maybe Wolfgang has already done the experiment to prove it. It certainly sounds reasonable.
That led me to think; instead of you destroying GPS devices on a regular basis and blowing computer resources on mining Bitcoins, you could you use your powers for good, and seed an Open Source BoardsurfrCFD software and/or a cloud based CFD community. Besides, my forearms are getting very sore from angle grinding.

I just read a book on Creativity and Innovation. A couple of points stuck with me. Firstly the vast majority of invention is simply building on ideas that are already in place. Very few inventions, innovation and advances are completely 'out of the blue'.
Secondly - their definition of genius was 'a person who makes the most amount of mistakes in the shortest period of time'. With the the view that the mistakes will lead to something truely innovative.
Thirdly, it was more important to share the mistakes than the final innovation.
So, to bring it all back to me, please post your stuffed fins /designs, because I am really lazy and would like to try an avoid angle grinding an abomination into life if someone has already done it.

PS. Sim-flow is an free Open source CFD package for Linux (yay!) and Windows. I have had a quick look at it - I think it might do the job, but I am going to need to spend a lot more time learning how it works: it's way above my pay grade atm.

Tips - Neighbours get tired of listening to angle grinding when they are watching TV at night.
- You have really bad lawn beetle.

I was thinking of using an inverted bevel, that is, undercutting at least the leading edge section and the base. The idea was to provide a physical lock for the foam/resin and also provide protection for the resin joint (as per Decrepit' s technique with Stainless steel leading edges.) But I am happy for you to try all options/techniques Swindy, and simply let me know what works.

Swindy said..

Is it worth the extra greif of trying to tuck wetted glass into the internal bevel as it is not the leading edge. With an external bevel it will still be locked in. Also it will be realy hard to bevel the inside all the way round with such sharp corners.
This is why I wanted you to do yours
first but I cant wait that long.

Good point mate and I agree. You will have to wait for the gurus to post - I fresh out of ideas now...

Might be a heck of a lot quicker to use polyester too. With a different foam of course. Something like gap filla.

Swindy said..

Is that polyester cloth like fangys flowery blouses or polyester resin ? I like the idea of gap filla.

Such a peasant! My blouses are silk.

keef said..
I wouldn't use polyester as there is flex in the fin , polyester hasn't got a lot of flex, epoxy is the go

That's a good point. I wonder how much the fin would flex with the middle section cutout? Unsurprisingly there is zilch in the solid version. Swindy, clamp up the box and jump up and down on the your cut out version. If it doesn't flex with that challenge, it just ain't gonna flex.