Finally got some machine time assigned to the CNC'd Fangy fin. Result is pretty good for a first attempt. There was some lessons learnt and will discuss in more depth with Fangman. Essentially some vibration near the tip on the final side that should sand out ok (the side with writing on where you can see some tidying up happening). Pictures of the process and end result. For those interested it was cut on a 4 axis CNC. The fin was initially held in the 4th axis to drill the bolt holes and cut the universal box basic shape. Then the fin bolted horizontally and basic 3 Axis machining done to cut out the mounting recesses and cut one side. Then the fin flipped, the universal box held in a custom jig and the other side machined with small bridges left to hold the rest of the fin. Next step will be final sanding but will be trivial compared to normal cast fin. Was hard waiting to get this far but in the meantime invested in some proper anodising dyes, degreaser, desmut/deox, Nickel based fixer and an Urn to help keep the now 4 different baths and their correct temps. Need to do a couple test anodises with the real chemicals before dunking this one.

So good Flex! I cant wait to see it for real. Standby for info into your inbox to get the tweaks right and so we can play with more toys as a bonus... If there is anyone out in SB World with some good CAD skills, who wants to come and play, please pm me as we might need some help finessing some of the finer details of the designs when we change them from being casting optimised over to CNC optimised.

Flex2 said..
Forgot to include a closeup shot of the universal box connection which is one of the two main advantages of a CNC version (the other being you can anodise or hard anodise it much easier than cast...and no porosity!). I did a quick test fit and seemed ok but will do more thorough tests over the following days including drilling out the Tuttle holes to try them out. I think and hope I followed all of Fangman's instructions correctly. Otherwise will have to butcher this fine artwork like the rest of my Fangy's

Looks lovely!

John340 said..
Does the CNC version weigh more than the cast version?

Good question. The CNC version with no finishing is weighing in at 963g and the cast version at 992g. However the cast has had the flange knife edged, sanded and bead blasted and this particular version requires epoxying the universal box mount to build up volume (Fangman getting sick of grinding). The CNC version I need to grind the flange to knife edge (error not changing the design prior to machining) and do all the finishing. This will further be in the CNC's favour so when all is said and done I would estimate 100g saving on the CNC version for a FF18_V4. You can see the designs are slightly different but in my understanding this is just the position of the fin mount....(the cast version is 30mm further back)

Fangman has corrected me, the cast and CNC designs look similar but they are different so any weight comparison here is pointless. I've traced out the two designs..the CNC version is the solid line and the cast is the dashed line when the flanges are aligned. The cast version has more area in the trailing edge where the CNC version has more area on the leading edge...to the eye its roughly the same surface area but due to the various profiles its not valid to compare cast vs CNC weights using these two different models. Will be fun see which one handles better....but with almost complete lack of wind here this may take some time.

fangman said..
Doldrums lead to idle minds and much more mucking about, not just with acid and electricity. This time it was a eucalyptus stick and some sandpaper. I wanted to start investigating whether a tip bulb on a relatively thin foil could improve the handling and lifting performance of a shallow water heavy weed fin enough to offset the increased drag.





The bulb is a NACA 64 series, at a nominal 12% rotated around its long axis. For safety reasons, the working fin bulb will have a trailing tip that is blunted.
Happily, Flex is a machine and never sleeps, so I let him do all the hard work creating and aligning the virtual bulb on the existing FF18V4. Screenshots as per Flex - thanks again mate :-)

The bulb acts to decrease pressure losses at the tip and disrupt the tip vortex itself. Theoretically, this should give rise to improved lift and better ventilation resistance. The latter occurs due to a disrupted tip vortex that does not persist with the same intensity downstream and thereby doesn't provide a pathway for ventilation.

I also wanted to try and make a fin that would not sink into soft mud quite so readily when doing a drag water start and instead act a bit like a sled. Of course, there is a good chance it will simply act like a plough, but in future one of the mods will be a flattened bottom section to increase the contact area.



The bulb is markedly oversized in its initial form. This is simply to give me a benchmark that I can compare to as I whittle the size down in subsequent iterations. Apart from decreasing the volume of the bulb overall, other modifications that I might try include a degree of camber on the lower surface and an increased tendency toward a platypus tail shape.

Speaking of vertical lift, I am not sure whether this will help reduce board wetted area (combined with a changed aft stance), or simply drive the nose down and make things worse.

Obviously, there is a considerable drag penalty involved, especially at very low angles of attack. I would guess heavy weed would induce comparatively greater drag too.

I assume this has been done before somewhere in windsurfing's past by some clever fellas who concluded it was a dud, but even if it is an anchor, I reckon at the very least it could be mounted as a cool looking trophy.

I see your channeling your inner ben Lexcen

powersloshin said..
Next will be a swinging fin

Got one, it's on a Mistral OD

remery said..

viz. Strata Skeg.

... and I am guessing you have still got one in your collection. Have you got a pic of it somewhere?

If you're aiming to reduce the tip vortex, what about "winglets" like you see on airplane wings? Once again, that's also something that's probably been done before as well! Of course, you'd need two because we use our fins symmetrically, and the interface between the main foil and the two winglets would be a tricky thing to get right...

ozzimark said..
If you're aiming to reduce the tip vortex, what about "winglets" like you see on airplane wings? Once again, that's also something that's probably been done before as well! Of course, you'd need two because we use our fins symmetrically, and the interface between the main foil and the two winglets would be a tricky thing to get right...

These fins are made specifically for dense weed, I don't think winglets would be a lot of help!

Winglets would be ideal, but as Decrepit mentioned, thick weed is a bit of a drag on their use. Also, the physical durability of the winglets given the amount of time I crash into the Real estate in the shallows could be a problem. The winglets ideally would be a thin profile because the Re number is so high but as such, fragile and prone to being damaged. Eg:




I will start with the bulb, and with time on the water, if it's not a complete anchor, flatten the base to create a slight camber and then evolve(grind) hollows along the lateral edges to develop a rudimentary and very short wingspan foil shape. I am not sure whether increasing the foil efficiency here will be worth the drag penalty. Especially at low AoA when the bulb/winglets will be generating vertical lift and potentially driving the board nose down. Consequently, will board surface drag be increased in addition to the fin bulb drag, or will the bulb allow a more aft stance and flying the fin sooner?

Since the cost to Anodise 1 fin locally is $100 and the cost of chemicals was about the same I figured it was better to try DIY first. Bought recommended cleaning, desmut/deox, dye and seal chemicals. That was the easy bit. It took forever but I finally got my new tanks to seal. Only worked out the problem after trying to make another DIY GPS. Issue was I was using left over Abrasion resistant Polycarbonate from other project...for whatever reason the Abrasion resist layer does not like Dichloromethane. It sort of bonds in places but endless pinhole leaks led to lots of frustration. All could have been avoided by using normal Polycarbonate or sanding the bond area first. I needed at least 3 polycarbonate tanks as temperatures needed to be at 60, 70 and 100 degC. The other two tanks needed to be room temp. The first two tanks used acrylic.

The Fangy fin still keeps on giving as there is no commercial tank on earth that fits a Fangy fin that anyone can afford the chemicals to fill. The Caswell guys recommended going with Urn and placing the tanks inside the water bath...trouble is polycarbonate is unbelievably good insulator so takes forever to get to temp (2hrs to get to 60degC with 6mm polycarb at 2Kw if you need to know)...since I needed 3 tanks super hot at nearly the same time this became problematic...in parallel started learning to Tig weld so tanks would heat quickly in the Urn but if anyone has tried its not recommended to start on 1.6mm stainless and trying to build a tank that can seal. Long story short..I managed to seal the pin hole leaks with piles of silicon which survived 100degC for a few hrs.

So today tried the dummy fin sample with good result. Threw the CNC FF18V4 in (after 2hrs final sanding whilst watching the dummy sample). Took fin to 2000 grit. Cleaned with Gumption (soft scrub), then hot soap bath then into the Caswell chemicals. The Aluetch chemicals are super vigorous and after 10 mins after heavy rinsing resulted in weird pattern sort of matching contours of fin. So cleaned for another 10 minutes with no change.

Dumped into Deox/Desmut bath and all pattern disappeared within seconds. The actual anodising was very boring and zero black goo. Dye tank looks orange but comes out bright violet.

Pictures here in fading light...not perfect Will be interesting to see if any longevity in the coating. (edit the white bit on leading edge tip of lawn photo was because I put on newspaper...rubbed off ok thankfully)

I emptied the tanks this morning after letting them cool overnight (takes a long time to cool as Polycarbonate is such good insulator). Unbelievable amount of black goo in the bottom of first clean tank (Aluetch). As mentioned the action in the clean tank is vigorous to bordering on violent. Hard to see from photo but at least a full tablespoon of solids plus a couple of cups of contaminated solution. Rest of tanks perfectly clean with no sediment. Previously all the black goo came out in the Ano tank. Considering this is a clean Al CNC'd billet it implies the previous cleaning using NaOH with the cast fins is woefully insufficient. Will be interesting to see if cleaning cast fins with the same stuff gives better result. I probably should have not held the fin in the dye quite as long (10 mins) as result would have been shinier. I also sprayed the fin with baking soda solution after coming out of acid to neutralise(didn't do this with the dummy fin, just rinsed with water)...can't be sure but think this may have caused the slight blotchiness compared to the test sample. Might use 2 more tanks in future, one to neutralise, then another to clean prior to dying. Luckily they can just be buckets.

Not to mention the mysterious contours, appearing and vanishing.
Great to see all that effort coming to fruition Flex. Amazing stuff

remery said..
The contours look like Damascus steel!

It is like a Domascus steel , kind of . This is where steel is layered over itself creating the lines where they are stuck together .
When plate steel is made , it starts as a block of cast . It is then squashed through a series of rollers getting progressively smaller . Doing this changes the random soup into a gran structure , more ,closer to the surface . It also removes air pockets .The more times it's done the better the product to a point . That's why thin sheet is stronger than billet even though they start the same . This is what produces the layered grain structure which your seeing . Like a tree trunk . You can count in the pic how many times the piece of steel went through the rollers .
There is much , much more to it than that . I would love , and could , crap on for hours , but I gave you the condensed version .