I think there is some special kind of love going on there. It's in the other part of the vid that he can't show. Those Fangy fins are versatile. All you need is imagination and a quiet spot without police.
Select to expand quoteMobZ said..
Ok, advice taken, mast track back. Getting comfortable. Feeling some magic. Thanks.
Smiles on dials is what we are all about. Fab to see MobZ, and also, what a beautiful looking spot. I agree with the above peeps, your set up and trim looks sweet. All you need to do now is burn some old kit in your backyard as a sacrifice to Huey and you will be pushing Kato in no time. ( and yes Kato's effort still messes with my head)
Time for a bit of an update. Flex's fission reactor method of prototyping is being refined with every fin we make and break.
This bit of kit was one of the first ones. The idea was to use this fin and then polish off the bulb and ultimately the trailing edge ellipsoid and see what difference it made. The initial fin looked pretty cool.
After a few sessions, I snapped off the entire tip off back to the carbon rods. I suspect my woeful construction and resin injection were a significant part of the early failure. The continued proving of the effectiveness of the bulb on my aluminium FF18 (and Flex's pool spinner results) makes me think I will revisit these two devices in the near future.
The next effort is much better and although still has a number of mistakes, it is quite an acceptable bit of kit.
Being a clumsy fart hasn't helped the trailing edge, but did lead to the placement of a cut out that seems to be big enough to be significant in its effect...possibly.
Flex made this fin also, his version has only a fraction of the amount of carbon rod, plus a flexible trailing edge strip. Flex duly tested the two fins back to back. The polar plots show the less carbon with flexible trailing edge version goes upwind better, but suffers from more spin out. Apart from the above flexing bits, my non-intentional cut out is the only difference between the two. I am sure Flex will post something when we figure out which component is making the difference. Meanwhile, the next fin is in the works, once again with an evolving construction technique and a few more ideas to try.
FF WTF#4 With each iteration Flex prints for me I am getting better at the resin side of things, and the overall number of stuff ups is getting less. There is a reduction in the diameter of the carbon rods to taper the stiffness toward the tip a little. The stainless fin bolts are now embedded deep within the fin foil itself, hopefully taking advantage of the good compressive strength of this technique and minimising its weaker tensile properties. Finally, the relatively lightly loaded rods at the leading edge are all eucalyptus dowel. Dowel is is cheaper, and lighter than same resin volume. Whilst, not having the strength of the carbon rod, it is a small fraction of the cost.
The epoxy resin I use is expensive, but has the advantage of a hard surface and allows me to pour thick sections (5cm) without problems with a runaway exothermic reaction. The downside is that it takes a week to cure. My patience is being sorely tested.
Select to expand quotefangman said..
FF WTF#4 With each iteration Flex prints for me I am getting better at the resin side of things, and the overall number of stuff ups is getting less. There is a reduction in the diameter of the carbon rods to taper the stiffness toward the tip a little. The stainless fin bolts are now embedded deep within the fin foil itself, hopefully taking advantage of the good compressive strength of this technique and minimising its weaker tensile properties. Finally, the relatively lightly loaded rods at the leading edge are all eucalyptus dowel. Dowel is is cheaper, and lighter than same resin volume. Whilst, not having the strength of the carbon rod, it is a small fraction of the cost.
The epoxy resin I use is expensive, but has the advantage of a hard surface and allows me to pour thick sections (5cm) without problems with a runaway exothermic reaction. The downside is that it takes a week to cure. My patience is being sorely tested.
Can you do a post cure in an oven or hot box to speed up the cure to max hardness?
Select to expand quotepeterowensbabs said..
Can you do a post cure in an oven or hot box to speed up the cure to max hardness?
I am a tad "Once bitten twice shy" after I melted the first one. I do get that it's post cure so it's a different scenario, but should I be concerned about melting the original 3D print framework? I am not sure how of how much structural significance, if any, it plays in the final scheme of things. I have been leaving it out in the sun under a dark rag, so it's getting a degree of post cure at least.
Select to expand quoteka43 said..
Thats a sweet looking fin Ross!!!!
It's got some funky stuff going on with the foil as it transitions from root to tip, so we will see if it goes as well as it looks...
Select to expand quotefangman said..peterowensbabs said..
Can you do a post cure in an oven or hot box to speed up the cure to max hardness?
I am a tad "Once bitten twice shy" after I melted the first one. I do get that it's post cure so it's a different scenario, but should I be concerned about melting the original 3D print framework? I am not sure how of how much structural significance, if any, it plays in the final scheme of things. I have been leaving it out in the sun under a dark rag, so it's getting a degree of post cure at least.
I would imagine loosing all the 3d printed part would in fact be good as it would have stuff all structural integrity. Can you melt it out and back fill with a castable epoxy similar to lost wax casting? Epoxy is so much stronger after a post cure...in orders of magnitude. 72 degrees is the minimum, the exotherm of the resin itself gets up around that usually (depending on it ratio) but its keeping it up there for 6-10 hours that makes it so much stronger. 70 is not hard to achieve with a good fan heater and an insulated box.
Would have to disagree with previous statement that 3D prints have stuff all structural integrity. In two dimensions they are as strong as whatever material you print with. You can of course 3D print with metal if you want to take it to the extreme. Check out 'Relativity Space' who are making fully 3D printed rockets. The main weakness in hobbyist 3d prints is the layer to layer bonding and I've been pretty successfully getting around that and making useable fins and other stuff using a system of transfer plates and bolts to crush the layers together or gluing the print around thin stainless steel sheet to take the tensile loads. Another way is just adding a single layer of fibreglass over the print.
Then I discovered gyroid infill which allows filling the void space with epoxy or expanding foam etc. I would suspect that the result is similar to fibreglass where the combination of epoxy makes the result stronger than either of the components. The beauty of 3D prints is you can adjust the infill amount so instead of trying to melt out the print you could just reduce the infill to 0% which would just be the shell. However, I've been using 15% infill as this seems around the point of most strength, cheap cost and fast print. These fins are printing in 5hrs or less.
The last few fins Fangy has been posting pics of all have carbon stiffeners or wooden dowel to save epoxy cost. However, in addition to costing more and making it more complex to design/fabricate I think this is decreasing the overall strength, especially in thin sections as it hinders getting the epoxy into all the spaces. I've just finished a couple of fins that have zero carbon stiffeners or steel bolts and the result appears extremely strong and stiff.
So strong and stiff it appears plenty of space could be used for other stuff. Other stuff could be lots of things. I put a whole bunch of ideas into one of Fangy's funky fins but there were so many new variables in play it was a bit of a dogs breakfast. See video below. In this fin I stuck a battery, a charge port, a LED and some simple latch electronics triggered by a reed switch to test the power supply to run a servo. I made it an identical fin to Fangy's but also put a flexible trailing edge and flexible bulb. The idea was to do an apples to apples comparison to test the flex idea. Got this idea from Rick who sails regularly at my home spot who made his own fin with a mono film trailing edge. He reckons the fin 'feels smoother' and points upwind better. I used 0.5mm PETG sheet but this may not be flexible enough based on footage from fin cam except for use as a bulb. The apples to apples test didn't go as planned as Fangy had cut a small notch in his fin and this seemed to make his fin much more immune to spinout.
So I've made a couple of standard Fangy 22's, which I have many hrs on so comparing if this flexy trailing edge stuff does anything should be easier. One has a 0.15mm mono film edge and one with 0.5mm PETG.
There is a big safety advantage of a flexible trailing edge that it stops fin cuts. A flexible bulb also eliminates the real possibility of being impaled. It seems like a good concept that it copies nature more. Fish fins and bird wings are strong at the leading edge and completely flexible to extremely delicate at the trailing edge.
Enough waffle for now. Video below for those interested.
Awesome, but umm, just making sure you are on to it already Flex, but I can't see where the flux capacitor going to fit?
I feel I must apologise for being such a rubbish science lab partner and making a mess of the comparison tests. It's mainly because, as you are rapidly discovering, I am not that fab at following instructions. So compared to your fin, my fin had a lot more carbon stiffening rods, and two thin layers of West Systems epoxy on the print surface to seal it. As a result, I am not sure that we can attribute all the performance difference to the unintentional cut out. I suspect that the stiffness of my fin might be factor that we need to consider.
I still haven't had a chance to get the latest proto wet. At least its fully cured now! Fingers crossed for this weekend.
You two guys never fail to dazzle me with your inventiveness and perseverance. !!! 
Interesting timing. For sure your fin had more carbon and you used different epoxy but in terms of stiffness it was marginal. They were both super stiff. The test however was dubious at best as was extremely low wind day so 8.6 sail on small board and small fin. For sure though in the 'tiny' chop your fin did way way better than the flexy fin which was opposite expected. Of course only way to verify is to make similar cutout on the flex fin (done) or, preferably do the experiment on a known standard fin without all the Fangy new weird stuff going on and with identical builds.
So today completed two FF22 fins, one with a 0.5mm PETG trailing edge and one with 0.15mm monofilm trailing edge. Zero carbon stiffeners, no transfer mech, bare min stainless threaded rod. Total cost for each fin was sub $20. Comparison photo below with the original FF22 cast Al (reddish Anodising) but you can see after 6000+km it is more like a FF18. Transparent is the 0.5mm and blue is the monofilm. Thus for a proper test might have to borrow/steal/print an original FF22. (ya, just realised the tuttle position on original Al is way different to the prints)
Since these two fins are pure 3D prints with zero stiffening I thought I'd make a jig to see if they can handle the loads before I put my life on the line. Thanks to Elmo for the test board. I used a Bunnings special bag of 20Kg pool salt to add a point load at 18.5cm from the board bottom and measured the deflection. This distance was about the maximum for the carbon fission fin used in the video/comparison which has a draft of about 20cm. The fully printed fin was also deflecting pretty wildly at this distance and slipped off the end of the fin just after I took the photo but the fin survived intact.
As you can see in the photos the full 3D print fin deflected about 12.5deg (measured in Fusion 360) where the carbon stiffened version was around 3deg. For comparison a good quality G10 Tribal fin (TWS 33) deflects 2.5 deg at same load. (please note there are measurement errors here but you can see from photos the rough result)
The load test showed that a fully 3d printed fin should be capable of surviving the loads required even if the flex is above standard fins. Whether the amount of flex at the tip is a good or bad thing can easily be solved by just one carbon stiffener down the leading edge or center of fin. This to me at least shows that a small cavity inside a printed fin can be used to make adjustable surfaces.
The 'flex/flux capacitor' or lets say power supply fits easily into the tuttle even with the transfer mech so the new design allows plenty of space for an ESP32 or micro servo etc. All of this can be bypassed by using hollow M6mm threaded rod (standard in many lamp shades) and feeding wires/control lines to top of board which of course makes further space to make adjustable rake/camber fins.
Nice work, Flex, keep going! I don't think flex is bad per se (no pun intended ). I think the problem with fins that are too flexible is that you also get twist, which basically reduces your angle of attack, and makes your lift-to-drag ratios go down. I think Kashy's "secret" for making the best formula fins was to give fins a lot of flex with minimal twist. Slowy might have mentioned something about orienting the layups for a similar reason, if I understood and remember him correctly.
Twist is obviously more of an issue with pointers or thinner weedies, but might still matter for deltas. I wonder what the best orientation of the carbon or steel rods be to minimize twist while allowing flex?
Flex on a raked fin can be just as bad as twist on an upright. well a high aspect raked fin anyway. A flexed raked fin, will act like a wing with -ve lift, producing a downward force.
Probably not as bad with a delta, as it flexes at a different angle.
You'd have to draw a diagram to convince me that a raked fin can produce a downward force due to flex. If it just flex (without twist), then it's still and upward force that is produced.
I can see how a weedie that is too flexible might feel like it is pulling the board down. But a fin that's too flexible due to bad design or construction will also have a lot of twist (unlike a good formula fin, with has a proper layup to have flex without twist). The twist reduces or eliminates the angle of attack on the lower part of the fin. So instead of producing most of the lift, the lower part only produces drag, making the fin basically equivalent to a shorter fin with more drag. The higher drag / lower lift combination will have the effect of pushing the nose of the board down.
as a fin flexes, it develops a horizontal component, with a rearward raked fin, this horizontal component is angled downward. with a forward raked fin the horizontal component is angled upward.
Here's a little thought experiment. Let's take a pointer fin with a layup that prevents twist, but allows flex. At speed, the fin deforms into a J-shape, as we have seen in underwater movies of formula fins. Basically, the fin acts as a J-type foil.
Now we rebox this fin so that it is now tilted back 45 degrees, and sail it at speed. The side ways forces bend it into the same J-shape. Looking at the flexing tip, the front edge is now lower than the rear edge, basically creating a negative angle of attack in this section. When this happens, that should indeed create a downward force, sticking the board to the water.
I think you and others have re-boxed pointer fins this way, so you probably verified this in practice. But what you saw is not an inherent limitation of weed fins - it's a result of a layup that was never intended to be used at a weedie angle, and is oriented wrong after re-boxing. For a weedie, you have to change the layup (or other reinforcements) so that flex is similar to a pointer - that is, perpendicular to the direction of travel, not the length of the fin. I know that the best weedies out there have a carefully designed layup, but the weedies that don't work well probably do not. For re-boxed pointer fins, I'd expect them to work well only if they are really stiff or short.
Yes Peter you've hit the nail on the head.
That was indeed the case with early weedies. As well as reducing the chord to thickness ratio by 20%, it gave them a bad reputation.
I guess it's possible to get the flex in the fin at 45deg to the chord, but I find it much easier to make it really stiff so it doesn't flex at all.
Yes, I think Fangy's alu fins are a very good example of how well stiff weedies can work. According to the designer of the Tectonic Weed and Speed Demons, one reason these fins are very good is that they use a much higher grade GFC than most other fins, which also makes them stiffer.
I'm starting to understand the effects of flex, twist, and bend curves a bit better, thanks to this discussion. Makes me wonder how many weed fins were designed by someone with a good understanding of the relevant factors. But I know of one brand designed in your area where that's certainly the case .
All my experience from working with the early assy and sym speed fins that Mal Wright made, through the Amac/Lockwood and Love fins, is "The stiffer, the better".
Now before you jump down my neck quoting all the fast world cup slalom and Formula flexy fins, note that I am speaking solely of SPEED fins here. 
Speed fins work at top speed at very low angles of attack. (Especially assy fins!) If you have even one degree of flex or especially twist, you are making a major change to the AOA of part of the fin. To the extent where that part is not working as designed, just producing drag, or worse!! In our testing and experience, this led to fins letting go at the most critical times 
When Tom Chalko was making the later Time Machine Assy Carbon fins, he kept getting them stiffer and stiffer, to the point that the best ones rang like a bell when you rapped them with your knuckle! The difference was easily noticeable.
This is even more evident in Raked fins.
One of the great things about weed sailing is that we use very short (low AR) raked fins, for obvious reasons.
But they seem to work much better than their AR and thickness would predict. I speculate that this is due to the 'endplate' effect created by the weed we are running through, and also to some extent by the close proximity of the lake bottom (yes, it is risky! )
But that also allows us to build quite short, thick G10 (and aluminium) fins that have virtually zero flex, and not need to use Carbon, which abrades very easily and quickly, and is much more expensive. Win/Win!
Early days but got our first wind in weeks today so did first test of the pure 3d print FF22 without any carbon stiffeners with two types of flexible trailing edge. In my haste to get out the door I left the original Aluminium FF22 in the shed so the test wasn't quite as planned. Didn't bother with fins cams etc.
However the results were a little surprising so sharing here. Please take all results with a pinch of salt as was sailing Melville which offers wind all over the place so further test required.
First both fins all survived with no issue despite pushing as hard as possible. This is a major milestone as reduces cost, complexity and speed to build.
Little to no spinouts and easy to recover if they did. Despite the fins being able to flex like in above photos it didn't seem noticeable. Fastest run was on the stiffer trailing edge fin but only because wind was stronger/lucky gust.
Most startling was the the upwind ability of the fin with mono film 'super flex' trailing edge (blue one in photo above) even though had less wind. Like Rick (the guy I got the idea off) said it gave a dramatic increase in upwind ability with no downside in speed. Attached polar plots (sorry boardsurfr, from GPSAR as can measure angles) show 8+ deg improvement upwind on both tacks. Hard to believe a windshift could have caused this but also hard to believe 5mm of flex plastic can do this. Logs on KA72 if anyone wants to check.
Nice first results, Flex. Can't wait to see more data. The monofilm trailing edge makes perfect sense to me, since it allows the flow at both sides to turn back to being parallel before combining. That should cut turbulences a lot. We likely push the fin hardest, into the highest angle of attack, when pinching upwind.
Regarding your original motivation of reducing cuts, Nina pointed out that you can get very nasty paper cuts from monofilm edges. She's gotten a few doing sail repairs. But the danger of deep cuts should be reduced when the trailing edge can bend.
I can highly recommend PVC as a fin material. ( short fat fin ). If you guys had access to a CNC mill. A bit flexy and tough as nails. I would think it perfect for the fins you guys are making.
Boardsurfr, cut my toe in half about 2cm deep last year stepping causally on an Al Fangy whilst launching. I acknowledge the mono film can cut but I'm of the opinion large/dangerous cuts will be avoided/minimised.
Imax, ya, I got a 6040 CNC mill plus I've even got an endless supply of free PVC (dumpster dive at the local plastic supply place) and have a large chunk of 50mm material ready to go. However with CNC so much is waste produced, the setup time is relatively long and the time it takes to machine plus the issue if you break a bit means you really gotta be watching the job all the time makes it a distant choice for me. For 3D print, 1 min setup to pause print about 1hr in to insert embedded nuts, push a button and walk away. Phone notifies you when print is ready to receive the nuts, stick them in and come back 4 hrs later with fin with 0.1mm tolerance and zero waste. Any stuff ups are fully recyclable. 10 mins mixing and injecting the epoxy and you have a fin. Add another 10 mins if you want carbon stiffeners.
Need to do an endurance test on these fins but I figure they are about 10-15 times cheaper than a standard fin so if they can get to about 400-600Km range they are competing economically with the near indestructible Al Fangy. This based as mentioned on the 6000Km my most used FF22 has done but is getting fairly long in the tooth. Please note I have no interest in competing with Fangy or manufacturing these, just means I can do 10-15 times more experimental fins for the same cost. The limitation for me is based on print size of my printer which allows max 25cm fins. However already been discussing with Fangy about dovetail joints in the fin to allow for fins outside current print dimensions.
I was about to delete all the video from the FF21.400.264.11 comparison test done earlier at Coods (Flex trailing edge vs Fangy stiff) as concluded it wasn't valid test as had two variables not the one hoped but realised I hadn't even looked at the footage. It was immediately apparent that the fin wake is considerably smaller for the flex trailing edge fin. Of course this reduced turbulence is what is expected as boardsurfr points out. This seems much more apparent in the smooth than the choppy stuff. Since Fangy had also introduced a small notch (which appeared to help with spinout) the effect may be caused by the notch and/or the stiffer trailing edge. I felt like I could push less on the flexy fin (which was opposite expected) which may explain the reduction in wake. Despite this, both fins headed upwind at exactly the same angle and speed. The flexy trailing edge in this case was 0.5mm PETG so I am expecting even less wake for the 0.15mm mono film fin if I stick a camera on. I uploaded a video (on my channel if you really interested) but snapshot below so you don't have to watch it to get the idea.
^ that's really interesting Flex. I would have expected the reduced wake, but not by that amount. I thought the bow wave from the leading edge of the fin would be far more significant. As usual your vids are a little goldmine of info.
Bit of an update. Took the pure 3D printed FF22 fins with the flexy edges out for another test but also remembered to bring the regular Al FF22 and camera. Was a lot choppier and windier and thought it would just be a spinout session. The two printed fins were completely solid in the chop, especially in the bear aways and had zero spin outs. The regular Al fin spun out a lot heading upwind but this was potentially due to it worn down to 18cm.
Interestingly, all 3 fins performed exactly the same upwind, though to be fair the 0.5mm trailing edge fin was tested last and wind/chop had died off and really only had one run. The fact the fins survived (just) the chop fest and performed better in some regards was a win. Looking at the video of the fin wake, it is difficult to call if any one fin had less or more wake.
After the session I noticed stress cracks forming around the rear embedded nut so thought better not risk heading out on these fins again. Made another mono film trailing edge fin up with nuts deeper into fin plus a few carbon stiffeners to see if stiffening the fin improves upwind performance and eliminates the cracking.
Whilst that was curing I went out on the light fin with the flexy trailing edge again but this time with a cutout filed into the rear like Fangy had done but bigger. I didn't bother with a camera but probably should have as the fin wake appeared much larger. Fin handled the chop much better with the cutout.
The conclusion is the cutout has a bigger effect on the visible wake than the flexy edge.
Attached pics of the stress cracks and the new fin. Seems there is a shortage of 8mm carbon rod which is the ideal size for fin stiffeners in the center of foil so had to go with 6mm and 4mm. Interestingly the addition of the carbon only decreased the flex by 1.5deg with the same 20Kg load. Hoping to test this new fin out tomorrow.
