Interesting. I did sand and polish my fin to 2000 and give it a polish with turtle wax. Only cos it looked sooo good being nice and shiny. Now I've never had an issue with spin outs and it's handling the chop really well. Still off the water atm but looking forward to further experiments

kato said..
Interesting. I did sand and polish my fin to 2000 and give it a polish with turtle wax. Only cos it looked sooo good being nice and shiny. Now I've never had an issue with spin outs and it's handling the chop really well. Still off the water atm but looking forward to further experiments

Kato, I'm pretty sure the detrimental effects come more from me changing the profile due to enthusiastically chasing some pitting out rather than the surface finish. Those flapper disks sure chew material quickly... You can clearly see the depression on the first polish photo. No one has reported degraded performance with finer finish so suspect it has something to do with what Decrepit said that an imperfect fin can get flow detachment with a polish finish. That said, I still got 4 PB's with this fin on its second run so it can't have been all bad. However, I was really struggling with the gybes on this day when usually flat water gybes are easy. I seemed to be crashing in many of the left hand turns and that depression was on the left side of fin...not sure I can explain why though...

I am on the final stages of getting some V4's ready for action. In the process I have found some laws of the universe cannot be thwarted. For instance, the Law of Certain Fail. Exhibit A. The FF18 V4's left the foundry, which is about 70 kms away from me, in late August. Australia Post, in their wisdom, decided to put them on a truck to Sydney. Once there, they sat untouched for two weeks (due to the congestion with lockdown) before they were put on a truck back to WA, and finally delivered just shy of one month after being posted.
Being keen as a bean, I immediately set to work and I was in the final stages of finishing when, of course, I dropped the fin while buffing. Toast falls butter side down, and fins always fall on a pointy bit. To uphold this indisputable truth, the fin fell toward the concrete trailing edge first. Just as I started to curse the imminent munting of trailing edge versus concrete, the Gods of Luck intervene by placing my power cord in the exact position to intercept the trailing edge before its crunched on the concrete. For a split second the fin is saved. Then the Gods of Sh!tf@ckery laugh and the trailing edge slices through the power cord and contacts the 240 volts of mischief within and just bursting to get out. Flash and bang! A lively short circuit across the fin for a microsecond before the RCD kicks in. Surely the odds of one neatly cleaved power cord and a fin saved from the concrete, but now with a neat chunk blown out of the trailing edge by the electric current, are too high to be just down to chance?

Great story but ****ty luck!!!

kato said..

RCD ???

Sorry my bad Kato: RCD: residual current device. An Important bit of kit to stop clowns like me electrocuting themselves.

en.wikipedia.org/wiki/Residual-current_device

Waisted or Wasted?

I somehow ended up reading up on the theoretically low drag Sears-Haack body. ( I have pasted in some links to the wikipedia entries for a summary of each item of interest for further backgrounding if you are really desperate to get to sleep)
en.wikipedia.org/wiki/Sears-Haack_body

This turned into reading some research on avoiding wave drag. This occurs primarily in the region of shock waves but exists in some form wherever there is a localised increase in pressure. Long story short, a bloke named Whitcomb came up with the a rule that dictated that an aerodynamic shape should change in cross sectional area as as smoothly as possible from front to rear in order to minimise wave drag.

en.wikipedia.org/wiki/Area_rule

Early supersonic aircraft had wasp-waist fuselage designs in order to accomodate the increased cross sectional area caused by the wings and tail.




All of this assumes that the plane has no yaw, which is not the situation on a fin, but I couldn't quite resist the temptation to do the experiment regardless. I realise given that the shock wave effects are due to a compressible fluid, which obviously water isn't, the theory doesn't extrapolate to hrdrodynamics directly. Quite possibly this might be yet another situation where I have applied the incorrect theory to situation and still get a result. Regardless, I have trimmed the fillet to create more area to diffuse and reduce the pressure peak in the area from the foil max thickness.

Exhibit A: Exaggerated Wasp Waisted FF (prototype 16 series foil shape)






I don't know how much reduction is required, so I have re-shaped the fillet to what I think is an exaggerated waist in the hope I will be able to pick some change, for better or worse, in the fin performance.
I think I can visualise what happens on the high pressure side, but the low pressure side is not so clear to me. What happens to the pre existing vortex flow that that was created by the fillet, does it get get disrupted or intensified or what?
If I feel there is something to be gained I will sit down with the CAD files and try and work out the amount of fillet reduction required in order to maintain the same cross sectional area.
So the next job is to try it out and see what happens.

Not wasted
First run yesterday. I can say with a good degree of certainty that the fin is no worse. It did not misbehave in any water conditions. It may just be confirmation bias, but the fin actually felt less draggy and consequently faster. Given this is almost the worst possible scientific method, there is lot more testing to come. On the plus side, because I have posted this on the interwebby thing, I am pretty sure some sort of magic happens whereby the sciencey stuff becomes automatically 100% factual and correct. In any case, the initial indications are that wasp waist FF might be on the cards as a recommended hack. More to come when I have trashed another few fin fillets ...

olskool said..
^ So the Waisted fillet is further research of Katos reduced fillet positive results?
Keenly following your findings.
Fangy, do you ever sleep???

I have it on good authority that Kato will soon be called to front ICAC to give evidence on the Corruption of Fillets, Fins and Physics 101, so I can't say anything more until this matter is heard.
As for sleep - yes defo. It's one of my strengths and possibly when I do my best work.

Somewhere back there.... Decrepit said something about polished fins and laminar detachment....

In that Fantasia period of my windsurfing speedsailing, distant history, when Mal Wright was designing and CNC cutting new assy speed fin prototypes every other week, (on this home made CNC machine!!! ) and Sandy Point was Duneless, crescent curved, sexy speed sailing heaven, Mal would come down on every good forecast with his new creations.

We had a cathartic relaxation routine every night before the big wind day, (quite a regular occurrence in that past era - the big winds I mean) sitting on the verandah, spray putty painting and wet and dry sanding fins to within an inch of their life - or is that a Micron? Of course, our conversation themes tended to focus around physics and mathematical stuff that Mal was fluent in, and I understood nothing of. But I kept asking dumb questions anyhow.

Somewhere in there I mused about the effects of polishing v's 800 grit matt finish and Mal decided we should experiment. It turns out that that soft 3D spray paint/putty stuff in a can polishes up really, really well with some very fine cutting compound paste and a soft cloth. We soon had some fins staring back at us with distorted versions of our own likeness! Slightly disturbing now I think about it, but we were on a mission and that part didn't register at the time.

i can definitively report that we noticed,................. absolutely no increase in speed, that could not be accounted for in about ten thousand other ways. Blind controls we didn't have.

BUT! One thing I did notice was that on almost every first run with the mirror finish fins, I felt.... a kind of intermittent incipient spin out. I called it squirrilly in the complete absence of any kowlegable, technical expertise to describe the phenomenon. It's not something you would call a positive outcome for your confidence.

The strange thing was that subsequent runs (yes, amazingly I persevered in putting my body on the line for the sake of science), that effect seemed to quickly disappear on second or third runs, and the fins behaved in a much more familiar way. That is to say, rock solid and FAST!

We never did formulate a good hypothesis to explain this observation, but maybe it was related to the very thing that was mentioned above somewhere by the great, wise, 'Decrepit' elder of windsurfing about detachment of laminar flow, and perhaps proposed what we didn't want to believe: That all our meticulous sanding, didn't work like we thought it should .

Shrug?!

Those good old days of Sandy Pt. in it's prime, sure were fun though.

Just a few of the early TM asymmetrical prototypes Mal Cut: left to right (roughly) V1, V2, V3, V4n, V4r, and god knows what the two on the right are, but they were all Srarboard tack assys.

decrepit said..

sailquik said..
>>>>maybe it was related to the very thing that was mentioned above somewhere by the great, wise, 'Decrepit' elder of windsurfing about detachment of laminar flow, and perhaps proposed what we didn't want to believe: That all our meticulous sanding, didn't work like we thought it should .

Shrug?!

Those good old days of Sandy Pt. in it's prime, sure were fun though.

Thanks Daffy, but I was only repeating what Mal had said somewhere. Something along the lines of, high polish only works on perfect/near perfect foils, otherwise you'll probably get detachment, the creation of a small boundary layer helps the flow to follow the foil's curve.
I'm not surprised Mal tried a high polish, as I'm sure his foils would have been very good.

Yes, but you remembered it! I am sure I have heard such gems many times and they have completely escaped me now.

Oh yes, the fins were cut to amazing tolerances, and became 'micron' accurate when he went to professionally CNC machined moulds for the V7 and V8 Carbon moulded models.

I wondered if the polished effect/shine or something Hyrophobic in the paint, polish or cutting compound wore off after a couple of runs.

Maybe it supports my now lazy notion that lots of fine filling and sanding does not improve a foil that is very good to start with?

I thought that I would do an update as I've been playing with the FF28 for a bit now.
I've now tried polish v unpolished and although there wasn't much speed difference the polished felt slipperier and I would probably continue with the shine.
This fin was designed to get me to 30kts in 8/10 kts which it does but I'm finding the I'm using it more and more in stronger winds. (20Kts with a 7.7) Its opened up some areas that we don't sail cos its just too shallow. Yesterday was a perfect example as I could explore the shallow areas as the rest were still playing on the edge in the chop.
The rake also means that when you hit something its not so brutal. I unfortunately hit a large stingray at 25kts, not so good for the ray but I didn't crash. Hopefully it survived.
No issue with chop either which was a surprise, It reconnects really when bouncing out of the waves, yes I took it for a play into the surf. Small waves.
Look forwards to returning to Lake George and chasing some higher numbers with this fin now that I had some solid sessions with it.

Tardy said..
Sounds like you can throw all your other fins away Kato ..it's turning out to be a allrounder
looks like I'm about to sand my fillet

Not yet, but it is pretty great for light wind and weed.
I do want to confuse Ross and get it to 40kts too

Had the pleasure of sailing with the Fangman a few weeks ago on his home turf. As nearly always, was sailing with my first Fangy fin22. The one I butchered anodising 11 months ago. First time though the master Fangy checking it out. Despite a lot of distance he reckoned it was holding out very well. ( I haven't calculated exact distance logged on this fin but it must be in the order of 4000km. Mostly in weedy abrasive conditions and lots of dredging. All posts logged but can't find a way to easily determine actual distance but some out there might be able to.)

With the complete absence of any wind I was motivated to have another crack at anodising my other 3 Fangy fins (and hopefully soon one from the Fangy fin skunk works). I have my favourite light wind 24, my ultra light wind 28 and my high wind 20 (cut to 18). All fins except the 18 have had lots of use where as the 18 has had one run in marginal conditions and I could not get upwind at all (finish was 40 grit pass of 20 seconds)

From the first attempt and reading more, the surface finish is key to getting a nice anodising coating. It was/is pretty clear that my first attempt (look further back in this thread for photos) was surface finish was lousy. I blame polishing as you can polish over a surface and it looks great but the underlying surface is pretty dodgy.

So this time around I spent a lot longer with the 1200 grit paper and whilst tedious it really started to show the underlying grain structure. Polishing at any time and it looked a million dollars but hitting it with the 1200 again you could see the effects highlighted with the dye in my first attempt.

It was a law of diminishing returns so after way too long with the 1200 grit I called it and brought out the polish. There was still porosity but I have a feeling there is no way to completely eliminate the porosity. (I have 1500 and 2000 grit paper but thought I would try this finish as a starter)

Effort to this point = 4hrs

This time round I thought I would skip the desmut process. The thinking being the Fangy fins have lots of porosity and the etching just enlarges that porosity. To compensate I pressure washed the fin, hit it with methylated spirts, pressure washed, acetone then pressure washed, then hot soapy water/scrub/rinse/do it again.

Chucked it in the anodising esky and this time did 90 minutes at maximum current I could achieve from my 12V camp battery which was average about 15amps. The acid looked black this time. Skipping desmut starting to look like a bad idea.

Brought it out and fin looked a lot darker and there was what seemed like a speck of grass on the fin, could not blow it off so tried my finger...damm, huge finger print. ****, what to do...decided to cook it off and see the result so steamed the fin for a good hour++ (probably 2 hrs)

Brought it out and was surprised that the surface was finger paint. This black stuff washed off easily but just kept coming...at least the finger print also washed off. Truly unbelievable amount of impurities...First 2 attempts I did desmut with Castic soda and the acid is crystal clear. Note, I washed 4 times and each time the black **** kept coming out so pretty sure the back bits you can see in photo will disappear once on water.

Not sure if the anodising is fine and all the impurities came to the surface. (oddly you may notice the completely polished surface appearance is identical to the raw foundry finish of the Tuttle mount) Hoping the H2So4 tank that looks completely black will settle out overnight so I can salvage most of it otherwise you might see some cheap acid on the sell pages soon.

Moral of story: do sand finish as best as possible but do not skip desmut. Next fin in the queue is the 18. This time will desmut + organic dye

Photos below of original fin 11 months and many km on (the dye should only be where the anodising worked), polished 24 before anodising, finger paint after harden, finished fin, dirty H2SO4 tank

Nice one Fangman, electro polishing sounds like fun. I might try the caustic bath once more as is far cheaper and simpler solution.

Cheapest 85% Phosphoric acid I can find is $210 + GST for 20 litre. $160 + GST for 10 litre. It gets significant cheaper per litre to buy 200 or 1000 litres. Supplier is "All Chemical" in Malaga allchemical.com.au/shop/phosphoric-acid-85/ Delivery is $60+ as DG but can pick up for free. Its where I got my Sulphuric acid from.

My acid bath sort of settled overnight so will try the FF18 with that.

So we can have a yellow Fangy that glistens in the sun like a gold tooth .?
Titanium nitride ?

In the interest of doing an apples to oranges comparison (anodising is supposedly all about surface finish) and Fangman throwing down the challenge with his fancy Phosphoric Polish and big words high tech stuff..... I remembered whist decanting my contaminated acid from yesterday (lost only 500ml!) I'd bought some high grit sandpaper for some other project.

After a few hrs searching, I found the stash and proceeded to finish one side of the FF18 to 7000 grit. The sun was shining and it was kinda fun taking metal polish this far. Oddly the grain structure of the Al shows clearly at 1200 grit but slowly disappears for above grit. Right (starboard?) side of fin is finished to 7000 (first photo), other side is maybe 1200 grit (probably can do better) Yes, there is still porosity but some is never ending....will chuck this in the caustic bath, ano and dye tank tomorrow. Will the extra work with surface finish make any difference? Thinking I will skip polish step as can't find grit size of polish I was using. Standby for another exciting episode...